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- //===- RewriteStatepointsForGC.cpp - Make GC relocations explicit ---------===//
- //
- // The LLVM Compiler Infrastructure
- //
- // This file is distributed under the University of Illinois Open Source
- // License. See LICENSE.TXT for details.
- //
- //===----------------------------------------------------------------------===//
- //
- // Rewrite an existing set of gc.statepoints such that they make potential
- // relocations performed by the garbage collector explicit in the IR.
- //
- //===----------------------------------------------------------------------===//
- #include "llvm/Pass.h"
- #include "llvm/Analysis/CFG.h"
- #include "llvm/Analysis/InstructionSimplify.h"
- #include "llvm/Analysis/TargetTransformInfo.h"
- #include "llvm/ADT/SetOperations.h"
- #include "llvm/ADT/Statistic.h"
- #include "llvm/ADT/DenseSet.h"
- #include "llvm/ADT/SetVector.h"
- #include "llvm/ADT/StringRef.h"
- #include "llvm/ADT/MapVector.h"
- #include "llvm/IR/BasicBlock.h"
- #include "llvm/IR/CallSite.h"
- #include "llvm/IR/Dominators.h"
- #include "llvm/IR/Function.h"
- #include "llvm/IR/IRBuilder.h"
- #include "llvm/IR/InstIterator.h"
- #include "llvm/IR/Instructions.h"
- #include "llvm/IR/Intrinsics.h"
- #include "llvm/IR/IntrinsicInst.h"
- #include "llvm/IR/Module.h"
- #include "llvm/IR/MDBuilder.h"
- #include "llvm/IR/Statepoint.h"
- #include "llvm/IR/Value.h"
- #include "llvm/IR/Verifier.h"
- #include "llvm/Support/Debug.h"
- #include "llvm/Support/CommandLine.h"
- #include "llvm/Transforms/Scalar.h"
- #include "llvm/Transforms/Utils/BasicBlockUtils.h"
- #include "llvm/Transforms/Utils/Cloning.h"
- #include "llvm/Transforms/Utils/Local.h"
- #include "llvm/Transforms/Utils/PromoteMemToReg.h"
- #define DEBUG_TYPE "rewrite-statepoints-for-gc"
- using namespace llvm;
- // Print the liveset found at the insert location
- static cl::opt<bool> PrintLiveSet("spp-print-liveset", cl::Hidden,
- cl::init(false));
- static cl::opt<bool> PrintLiveSetSize("spp-print-liveset-size", cl::Hidden,
- cl::init(false));
- // Print out the base pointers for debugging
- static cl::opt<bool> PrintBasePointers("spp-print-base-pointers", cl::Hidden,
- cl::init(false));
- // Cost threshold measuring when it is profitable to rematerialize value instead
- // of relocating it
- static cl::opt<unsigned>
- RematerializationThreshold("spp-rematerialization-threshold", cl::Hidden,
- cl::init(6));
- #ifdef XDEBUG
- static bool ClobberNonLive = true;
- #else
- static bool ClobberNonLive = false;
- #endif
- static cl::opt<bool, true> ClobberNonLiveOverride("rs4gc-clobber-non-live",
- cl::location(ClobberNonLive),
- cl::Hidden);
- static cl::opt<bool> UseDeoptBundles("rs4gc-use-deopt-bundles", cl::Hidden,
- cl::init(false));
- static cl::opt<bool>
- AllowStatepointWithNoDeoptInfo("rs4gc-allow-statepoint-with-no-deopt-info",
- cl::Hidden, cl::init(true));
- /// Should we split vectors of pointers into their individual elements? This
- /// is known to be buggy, but the alternate implementation isn't yet ready.
- /// This is purely to provide a debugging and dianostic hook until the vector
- /// split is replaced with vector relocations.
- static cl::opt<bool> UseVectorSplit("rs4gc-split-vector-values", cl::Hidden,
- cl::init(false));
- namespace {
- struct RewriteStatepointsForGC : public ModulePass {
- static char ID; // Pass identification, replacement for typeid
- RewriteStatepointsForGC() : ModulePass(ID) {
- initializeRewriteStatepointsForGCPass(*PassRegistry::getPassRegistry());
- }
- bool runOnFunction(Function &F);
- bool runOnModule(Module &M) override {
- bool Changed = false;
- for (Function &F : M)
- Changed |= runOnFunction(F);
- if (Changed) {
- // stripNonValidAttributes asserts that shouldRewriteStatepointsIn
- // returns true for at least one function in the module. Since at least
- // one function changed, we know that the precondition is satisfied.
- stripNonValidAttributes(M);
- }
- return Changed;
- }
- void getAnalysisUsage(AnalysisUsage &AU) const override {
- // We add and rewrite a bunch of instructions, but don't really do much
- // else. We could in theory preserve a lot more analyses here.
- AU.addRequired<DominatorTreeWrapperPass>();
- AU.addRequired<TargetTransformInfoWrapperPass>();
- }
- /// The IR fed into RewriteStatepointsForGC may have had attributes implying
- /// dereferenceability that are no longer valid/correct after
- /// RewriteStatepointsForGC has run. This is because semantically, after
- /// RewriteStatepointsForGC runs, all calls to gc.statepoint "free" the entire
- /// heap. stripNonValidAttributes (conservatively) restores correctness
- /// by erasing all attributes in the module that externally imply
- /// dereferenceability.
- /// Similar reasoning also applies to the noalias attributes. gc.statepoint
- /// can touch the entire heap including noalias objects.
- void stripNonValidAttributes(Module &M);
- // Helpers for stripNonValidAttributes
- void stripNonValidAttributesFromBody(Function &F);
- void stripNonValidAttributesFromPrototype(Function &F);
- };
- } // namespace
- char RewriteStatepointsForGC::ID = 0;
- ModulePass *llvm::createRewriteStatepointsForGCPass() {
- return new RewriteStatepointsForGC();
- }
- INITIALIZE_PASS_BEGIN(RewriteStatepointsForGC, "rewrite-statepoints-for-gc",
- "Make relocations explicit at statepoints", false, false)
- INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)
- INITIALIZE_PASS_END(RewriteStatepointsForGC, "rewrite-statepoints-for-gc",
- "Make relocations explicit at statepoints", false, false)
- namespace {
- struct GCPtrLivenessData {
- /// Values defined in this block.
- DenseMap<BasicBlock *, DenseSet<Value *>> KillSet;
- /// Values used in this block (and thus live); does not included values
- /// killed within this block.
- DenseMap<BasicBlock *, DenseSet<Value *>> LiveSet;
- /// Values live into this basic block (i.e. used by any
- /// instruction in this basic block or ones reachable from here)
- DenseMap<BasicBlock *, DenseSet<Value *>> LiveIn;
- /// Values live out of this basic block (i.e. live into
- /// any successor block)
- DenseMap<BasicBlock *, DenseSet<Value *>> LiveOut;
- };
- // The type of the internal cache used inside the findBasePointers family
- // of functions. From the callers perspective, this is an opaque type and
- // should not be inspected.
- //
- // In the actual implementation this caches two relations:
- // - The base relation itself (i.e. this pointer is based on that one)
- // - The base defining value relation (i.e. before base_phi insertion)
- // Generally, after the execution of a full findBasePointer call, only the
- // base relation will remain. Internally, we add a mixture of the two
- // types, then update all the second type to the first type
- typedef DenseMap<Value *, Value *> DefiningValueMapTy;
- typedef DenseSet<Value *> StatepointLiveSetTy;
- typedef DenseMap<AssertingVH<Instruction>, AssertingVH<Value>>
- RematerializedValueMapTy;
- struct PartiallyConstructedSafepointRecord {
- /// The set of values known to be live across this safepoint
- StatepointLiveSetTy LiveSet;
- /// Mapping from live pointers to a base-defining-value
- DenseMap<Value *, Value *> PointerToBase;
- /// The *new* gc.statepoint instruction itself. This produces the token
- /// that normal path gc.relocates and the gc.result are tied to.
- Instruction *StatepointToken;
- /// Instruction to which exceptional gc relocates are attached
- /// Makes it easier to iterate through them during relocationViaAlloca.
- Instruction *UnwindToken;
- /// Record live values we are rematerialized instead of relocating.
- /// They are not included into 'LiveSet' field.
- /// Maps rematerialized copy to it's original value.
- RematerializedValueMapTy RematerializedValues;
- };
- }
- static ArrayRef<Use> GetDeoptBundleOperands(ImmutableCallSite CS) {
- assert(UseDeoptBundles && "Should not be called otherwise!");
- Optional<OperandBundleUse> DeoptBundle = CS.getOperandBundle("deopt");
- if (!DeoptBundle.hasValue()) {
- assert(AllowStatepointWithNoDeoptInfo &&
- "Found non-leaf call without deopt info!");
- return None;
- }
- return DeoptBundle.getValue().Inputs;
- }
- /// Compute the live-in set for every basic block in the function
- static void computeLiveInValues(DominatorTree &DT, Function &F,
- GCPtrLivenessData &Data);
- /// Given results from the dataflow liveness computation, find the set of live
- /// Values at a particular instruction.
- static void findLiveSetAtInst(Instruction *inst, GCPtrLivenessData &Data,
- StatepointLiveSetTy &out);
- // TODO: Once we can get to the GCStrategy, this becomes
- // Optional<bool> isGCManagedPointer(const Type *Ty) const override {
- static bool isGCPointerType(Type *T) {
- if (auto *PT = dyn_cast<PointerType>(T))
- // For the sake of this example GC, we arbitrarily pick addrspace(1) as our
- // GC managed heap. We know that a pointer into this heap needs to be
- // updated and that no other pointer does.
- return (1 == PT->getAddressSpace());
- return false;
- }
- // Return true if this type is one which a) is a gc pointer or contains a GC
- // pointer and b) is of a type this code expects to encounter as a live value.
- // (The insertion code will assert that a type which matches (a) and not (b)
- // is not encountered.)
- static bool isHandledGCPointerType(Type *T) {
- // We fully support gc pointers
- if (isGCPointerType(T))
- return true;
- // We partially support vectors of gc pointers. The code will assert if it
- // can't handle something.
- if (auto VT = dyn_cast<VectorType>(T))
- if (isGCPointerType(VT->getElementType()))
- return true;
- return false;
- }
- #ifndef NDEBUG
- /// Returns true if this type contains a gc pointer whether we know how to
- /// handle that type or not.
- static bool containsGCPtrType(Type *Ty) {
- if (isGCPointerType(Ty))
- return true;
- if (VectorType *VT = dyn_cast<VectorType>(Ty))
- return isGCPointerType(VT->getScalarType());
- if (ArrayType *AT = dyn_cast<ArrayType>(Ty))
- return containsGCPtrType(AT->getElementType());
- if (StructType *ST = dyn_cast<StructType>(Ty))
- return std::any_of(ST->subtypes().begin(), ST->subtypes().end(),
- containsGCPtrType);
- return false;
- }
- // Returns true if this is a type which a) is a gc pointer or contains a GC
- // pointer and b) is of a type which the code doesn't expect (i.e. first class
- // aggregates). Used to trip assertions.
- static bool isUnhandledGCPointerType(Type *Ty) {
- return containsGCPtrType(Ty) && !isHandledGCPointerType(Ty);
- }
- #endif
- static bool order_by_name(Value *a, Value *b) {
- if (a->hasName() && b->hasName()) {
- return -1 == a->getName().compare(b->getName());
- } else if (a->hasName() && !b->hasName()) {
- return true;
- } else if (!a->hasName() && b->hasName()) {
- return false;
- } else {
- // Better than nothing, but not stable
- return a < b;
- }
- }
- // Return the name of the value suffixed with the provided value, or if the
- // value didn't have a name, the default value specified.
- static std::string suffixed_name_or(Value *V, StringRef Suffix,
- StringRef DefaultName) {
- return V->hasName() ? (V->getName() + Suffix).str() : DefaultName.str();
- }
- // Conservatively identifies any definitions which might be live at the
- // given instruction. The analysis is performed immediately before the
- // given instruction. Values defined by that instruction are not considered
- // live. Values used by that instruction are considered live.
- static void analyzeParsePointLiveness(
- DominatorTree &DT, GCPtrLivenessData &OriginalLivenessData,
- const CallSite &CS, PartiallyConstructedSafepointRecord &result) {
- Instruction *inst = CS.getInstruction();
- StatepointLiveSetTy LiveSet;
- findLiveSetAtInst(inst, OriginalLivenessData, LiveSet);
- if (PrintLiveSet) {
- // Note: This output is used by several of the test cases
- // The order of elements in a set is not stable, put them in a vec and sort
- // by name
- SmallVector<Value *, 64> Temp;
- Temp.insert(Temp.end(), LiveSet.begin(), LiveSet.end());
- std::sort(Temp.begin(), Temp.end(), order_by_name);
- errs() << "Live Variables:\n";
- for (Value *V : Temp)
- dbgs() << " " << V->getName() << " " << *V << "\n";
- }
- if (PrintLiveSetSize) {
- errs() << "Safepoint For: " << CS.getCalledValue()->getName() << "\n";
- errs() << "Number live values: " << LiveSet.size() << "\n";
- }
- result.LiveSet = LiveSet;
- }
- static bool isKnownBaseResult(Value *V);
- namespace {
- /// A single base defining value - An immediate base defining value for an
- /// instruction 'Def' is an input to 'Def' whose base is also a base of 'Def'.
- /// For instructions which have multiple pointer [vector] inputs or that
- /// transition between vector and scalar types, there is no immediate base
- /// defining value. The 'base defining value' for 'Def' is the transitive
- /// closure of this relation stopping at the first instruction which has no
- /// immediate base defining value. The b.d.v. might itself be a base pointer,
- /// but it can also be an arbitrary derived pointer.
- struct BaseDefiningValueResult {
- /// Contains the value which is the base defining value.
- Value * const BDV;
- /// True if the base defining value is also known to be an actual base
- /// pointer.
- const bool IsKnownBase;
- BaseDefiningValueResult(Value *BDV, bool IsKnownBase)
- : BDV(BDV), IsKnownBase(IsKnownBase) {
- #ifndef NDEBUG
- // Check consistency between new and old means of checking whether a BDV is
- // a base.
- bool MustBeBase = isKnownBaseResult(BDV);
- assert(!MustBeBase || MustBeBase == IsKnownBase);
- #endif
- }
- };
- }
- static BaseDefiningValueResult findBaseDefiningValue(Value *I);
- /// Return a base defining value for the 'Index' element of the given vector
- /// instruction 'I'. If Index is null, returns a BDV for the entire vector
- /// 'I'. As an optimization, this method will try to determine when the
- /// element is known to already be a base pointer. If this can be established,
- /// the second value in the returned pair will be true. Note that either a
- /// vector or a pointer typed value can be returned. For the former, the
- /// vector returned is a BDV (and possibly a base) of the entire vector 'I'.
- /// If the later, the return pointer is a BDV (or possibly a base) for the
- /// particular element in 'I'.
- static BaseDefiningValueResult
- findBaseDefiningValueOfVector(Value *I) {
- // Each case parallels findBaseDefiningValue below, see that code for
- // detailed motivation.
- if (isa<Argument>(I))
- // An incoming argument to the function is a base pointer
- return BaseDefiningValueResult(I, true);
- if (isa<Constant>(I))
- // Constant vectors consist only of constant pointers.
- return BaseDefiningValueResult(I, true);
- if (isa<LoadInst>(I))
- return BaseDefiningValueResult(I, true);
- if (isa<InsertElementInst>(I))
- // We don't know whether this vector contains entirely base pointers or
- // not. To be conservatively correct, we treat it as a BDV and will
- // duplicate code as needed to construct a parallel vector of bases.
- return BaseDefiningValueResult(I, false);
- if (isa<ShuffleVectorInst>(I))
- // We don't know whether this vector contains entirely base pointers or
- // not. To be conservatively correct, we treat it as a BDV and will
- // duplicate code as needed to construct a parallel vector of bases.
- // TODO: There a number of local optimizations which could be applied here
- // for particular sufflevector patterns.
- return BaseDefiningValueResult(I, false);
- // A PHI or Select is a base defining value. The outer findBasePointer
- // algorithm is responsible for constructing a base value for this BDV.
- assert((isa<SelectInst>(I) || isa<PHINode>(I)) &&
- "unknown vector instruction - no base found for vector element");
- return BaseDefiningValueResult(I, false);
- }
- /// Helper function for findBasePointer - Will return a value which either a)
- /// defines the base pointer for the input, b) blocks the simple search
- /// (i.e. a PHI or Select of two derived pointers), or c) involves a change
- /// from pointer to vector type or back.
- static BaseDefiningValueResult findBaseDefiningValue(Value *I) {
- assert(I->getType()->isPtrOrPtrVectorTy() &&
- "Illegal to ask for the base pointer of a non-pointer type");
- if (I->getType()->isVectorTy())
- return findBaseDefiningValueOfVector(I);
- if (isa<Argument>(I))
- // An incoming argument to the function is a base pointer
- // We should have never reached here if this argument isn't an gc value
- return BaseDefiningValueResult(I, true);
- if (isa<Constant>(I))
- // We assume that objects with a constant base (e.g. a global) can't move
- // and don't need to be reported to the collector because they are always
- // live. All constants have constant bases. Besides global references, all
- // kinds of constants (e.g. undef, constant expressions, null pointers) can
- // be introduced by the inliner or the optimizer, especially on dynamically
- // dead paths. See e.g. test4 in constants.ll.
- return BaseDefiningValueResult(I, true);
- if (CastInst *CI = dyn_cast<CastInst>(I)) {
- Value *Def = CI->stripPointerCasts();
- // If stripping pointer casts changes the address space there is an
- // addrspacecast in between.
- assert(cast<PointerType>(Def->getType())->getAddressSpace() ==
- cast<PointerType>(CI->getType())->getAddressSpace() &&
- "unsupported addrspacecast");
- // If we find a cast instruction here, it means we've found a cast which is
- // not simply a pointer cast (i.e. an inttoptr). We don't know how to
- // handle int->ptr conversion.
- assert(!isa<CastInst>(Def) && "shouldn't find another cast here");
- return findBaseDefiningValue(Def);
- }
- if (isa<LoadInst>(I))
- // The value loaded is an gc base itself
- return BaseDefiningValueResult(I, true);
-
- if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(I))
- // The base of this GEP is the base
- return findBaseDefiningValue(GEP->getPointerOperand());
- if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(I)) {
- switch (II->getIntrinsicID()) {
- default:
- // fall through to general call handling
- break;
- case Intrinsic::experimental_gc_statepoint:
- llvm_unreachable("statepoints don't produce pointers");
- case Intrinsic::experimental_gc_relocate: {
- // Rerunning safepoint insertion after safepoints are already
- // inserted is not supported. It could probably be made to work,
- // but why are you doing this? There's no good reason.
- llvm_unreachable("repeat safepoint insertion is not supported");
- }
- case Intrinsic::gcroot:
- // Currently, this mechanism hasn't been extended to work with gcroot.
- // There's no reason it couldn't be, but I haven't thought about the
- // implications much.
- llvm_unreachable(
- "interaction with the gcroot mechanism is not supported");
- }
- }
- // We assume that functions in the source language only return base
- // pointers. This should probably be generalized via attributes to support
- // both source language and internal functions.
- if (isa<CallInst>(I) || isa<InvokeInst>(I))
- return BaseDefiningValueResult(I, true);
- // I have absolutely no idea how to implement this part yet. It's not
- // necessarily hard, I just haven't really looked at it yet.
- assert(!isa<LandingPadInst>(I) && "Landing Pad is unimplemented");
- if (isa<AtomicCmpXchgInst>(I))
- // A CAS is effectively a atomic store and load combined under a
- // predicate. From the perspective of base pointers, we just treat it
- // like a load.
- return BaseDefiningValueResult(I, true);
- assert(!isa<AtomicRMWInst>(I) && "Xchg handled above, all others are "
- "binary ops which don't apply to pointers");
- // The aggregate ops. Aggregates can either be in the heap or on the
- // stack, but in either case, this is simply a field load. As a result,
- // this is a defining definition of the base just like a load is.
- if (isa<ExtractValueInst>(I))
- return BaseDefiningValueResult(I, true);
- // We should never see an insert vector since that would require we be
- // tracing back a struct value not a pointer value.
- assert(!isa<InsertValueInst>(I) &&
- "Base pointer for a struct is meaningless");
- // An extractelement produces a base result exactly when it's input does.
- // We may need to insert a parallel instruction to extract the appropriate
- // element out of the base vector corresponding to the input. Given this,
- // it's analogous to the phi and select case even though it's not a merge.
- if (isa<ExtractElementInst>(I))
- // Note: There a lot of obvious peephole cases here. This are deliberately
- // handled after the main base pointer inference algorithm to make writing
- // test cases to exercise that code easier.
- return BaseDefiningValueResult(I, false);
- // The last two cases here don't return a base pointer. Instead, they
- // return a value which dynamically selects from among several base
- // derived pointers (each with it's own base potentially). It's the job of
- // the caller to resolve these.
- assert((isa<SelectInst>(I) || isa<PHINode>(I)) &&
- "missing instruction case in findBaseDefiningValing");
- return BaseDefiningValueResult(I, false);
- }
- /// Returns the base defining value for this value.
- static Value *findBaseDefiningValueCached(Value *I, DefiningValueMapTy &Cache) {
- Value *&Cached = Cache[I];
- if (!Cached) {
- Cached = findBaseDefiningValue(I).BDV;
- DEBUG(dbgs() << "fBDV-cached: " << I->getName() << " -> "
- << Cached->getName() << "\n");
- }
- assert(Cache[I] != nullptr);
- return Cached;
- }
- /// Return a base pointer for this value if known. Otherwise, return it's
- /// base defining value.
- static Value *findBaseOrBDV(Value *I, DefiningValueMapTy &Cache) {
- Value *Def = findBaseDefiningValueCached(I, Cache);
- auto Found = Cache.find(Def);
- if (Found != Cache.end()) {
- // Either a base-of relation, or a self reference. Caller must check.
- return Found->second;
- }
- // Only a BDV available
- return Def;
- }
- /// Given the result of a call to findBaseDefiningValue, or findBaseOrBDV,
- /// is it known to be a base pointer? Or do we need to continue searching.
- static bool isKnownBaseResult(Value *V) {
- if (!isa<PHINode>(V) && !isa<SelectInst>(V) &&
- !isa<ExtractElementInst>(V) && !isa<InsertElementInst>(V) &&
- !isa<ShuffleVectorInst>(V)) {
- // no recursion possible
- return true;
- }
- if (isa<Instruction>(V) &&
- cast<Instruction>(V)->getMetadata("is_base_value")) {
- // This is a previously inserted base phi or select. We know
- // that this is a base value.
- return true;
- }
- // We need to keep searching
- return false;
- }
- namespace {
- /// Models the state of a single base defining value in the findBasePointer
- /// algorithm for determining where a new instruction is needed to propagate
- /// the base of this BDV.
- class BDVState {
- public:
- enum Status { Unknown, Base, Conflict };
- BDVState(Status s, Value *b = nullptr) : status(s), base(b) {
- assert(status != Base || b);
- }
- explicit BDVState(Value *b) : status(Base), base(b) {}
- BDVState() : status(Unknown), base(nullptr) {}
- Status getStatus() const { return status; }
- Value *getBase() const { return base; }
- bool isBase() const { return getStatus() == Base; }
- bool isUnknown() const { return getStatus() == Unknown; }
- bool isConflict() const { return getStatus() == Conflict; }
- bool operator==(const BDVState &other) const {
- return base == other.base && status == other.status;
- }
- bool operator!=(const BDVState &other) const { return !(*this == other); }
- LLVM_DUMP_METHOD
- void dump() const { print(dbgs()); dbgs() << '\n'; }
-
- void print(raw_ostream &OS) const {
- switch (status) {
- case Unknown:
- OS << "U";
- break;
- case Base:
- OS << "B";
- break;
- case Conflict:
- OS << "C";
- break;
- };
- OS << " (" << base << " - "
- << (base ? base->getName() : "nullptr") << "): ";
- }
- private:
- Status status;
- AssertingVH<Value> base; // non null only if status == base
- };
- }
- #ifndef NDEBUG
- static raw_ostream &operator<<(raw_ostream &OS, const BDVState &State) {
- State.print(OS);
- return OS;
- }
- #endif
- namespace {
- // Values of type BDVState form a lattice, and this is a helper
- // class that implementes the meet operation. The meat of the meet
- // operation is implemented in MeetBDVStates::pureMeet
- class MeetBDVStates {
- public:
- /// Initializes the currentResult to the TOP state so that if can be met with
- /// any other state to produce that state.
- MeetBDVStates() {}
- // Destructively meet the current result with the given BDVState
- void meetWith(BDVState otherState) {
- currentResult = meet(otherState, currentResult);
- }
- BDVState getResult() const { return currentResult; }
- private:
- BDVState currentResult;
- /// Perform a meet operation on two elements of the BDVState lattice.
- static BDVState meet(BDVState LHS, BDVState RHS) {
- assert((pureMeet(LHS, RHS) == pureMeet(RHS, LHS)) &&
- "math is wrong: meet does not commute!");
- BDVState Result = pureMeet(LHS, RHS);
- DEBUG(dbgs() << "meet of " << LHS << " with " << RHS
- << " produced " << Result << "\n");
- return Result;
- }
- static BDVState pureMeet(const BDVState &stateA, const BDVState &stateB) {
- switch (stateA.getStatus()) {
- case BDVState::Unknown:
- return stateB;
- case BDVState::Base:
- assert(stateA.getBase() && "can't be null");
- if (stateB.isUnknown())
- return stateA;
- if (stateB.isBase()) {
- if (stateA.getBase() == stateB.getBase()) {
- assert(stateA == stateB && "equality broken!");
- return stateA;
- }
- return BDVState(BDVState::Conflict);
- }
- assert(stateB.isConflict() && "only three states!");
- return BDVState(BDVState::Conflict);
- case BDVState::Conflict:
- return stateA;
- }
- llvm_unreachable("only three states!");
- }
- };
- }
- /// For a given value or instruction, figure out what base ptr it's derived
- /// from. For gc objects, this is simply itself. On success, returns a value
- /// which is the base pointer. (This is reliable and can be used for
- /// relocation.) On failure, returns nullptr.
- static Value *findBasePointer(Value *I, DefiningValueMapTy &cache) {
- Value *def = findBaseOrBDV(I, cache);
- if (isKnownBaseResult(def)) {
- return def;
- }
- // Here's the rough algorithm:
- // - For every SSA value, construct a mapping to either an actual base
- // pointer or a PHI which obscures the base pointer.
- // - Construct a mapping from PHI to unknown TOP state. Use an
- // optimistic algorithm to propagate base pointer information. Lattice
- // looks like:
- // UNKNOWN
- // b1 b2 b3 b4
- // CONFLICT
- // When algorithm terminates, all PHIs will either have a single concrete
- // base or be in a conflict state.
- // - For every conflict, insert a dummy PHI node without arguments. Add
- // these to the base[Instruction] = BasePtr mapping. For every
- // non-conflict, add the actual base.
- // - For every conflict, add arguments for the base[a] of each input
- // arguments.
- //
- // Note: A simpler form of this would be to add the conflict form of all
- // PHIs without running the optimistic algorithm. This would be
- // analogous to pessimistic data flow and would likely lead to an
- // overall worse solution.
- #ifndef NDEBUG
- auto isExpectedBDVType = [](Value *BDV) {
- return isa<PHINode>(BDV) || isa<SelectInst>(BDV) ||
- isa<ExtractElementInst>(BDV) || isa<InsertElementInst>(BDV);
- };
- #endif
- // Once populated, will contain a mapping from each potentially non-base BDV
- // to a lattice value (described above) which corresponds to that BDV.
- // We use the order of insertion (DFS over the def/use graph) to provide a
- // stable deterministic ordering for visiting DenseMaps (which are unordered)
- // below. This is important for deterministic compilation.
- MapVector<Value *, BDVState> States;
- // Recursively fill in all base defining values reachable from the initial
- // one for which we don't already know a definite base value for
- /* scope */ {
- SmallVector<Value*, 16> Worklist;
- Worklist.push_back(def);
- States.insert(std::make_pair(def, BDVState()));
- while (!Worklist.empty()) {
- Value *Current = Worklist.pop_back_val();
- assert(!isKnownBaseResult(Current) && "why did it get added?");
- auto visitIncomingValue = [&](Value *InVal) {
- Value *Base = findBaseOrBDV(InVal, cache);
- if (isKnownBaseResult(Base))
- // Known bases won't need new instructions introduced and can be
- // ignored safely
- return;
- assert(isExpectedBDVType(Base) && "the only non-base values "
- "we see should be base defining values");
- if (States.insert(std::make_pair(Base, BDVState())).second)
- Worklist.push_back(Base);
- };
- if (PHINode *Phi = dyn_cast<PHINode>(Current)) {
- for (Value *InVal : Phi->incoming_values())
- visitIncomingValue(InVal);
- } else if (SelectInst *Sel = dyn_cast<SelectInst>(Current)) {
- visitIncomingValue(Sel->getTrueValue());
- visitIncomingValue(Sel->getFalseValue());
- } else if (auto *EE = dyn_cast<ExtractElementInst>(Current)) {
- visitIncomingValue(EE->getVectorOperand());
- } else if (auto *IE = dyn_cast<InsertElementInst>(Current)) {
- visitIncomingValue(IE->getOperand(0)); // vector operand
- visitIncomingValue(IE->getOperand(1)); // scalar operand
- } else {
- // There is one known class of instructions we know we don't handle.
- assert(isa<ShuffleVectorInst>(Current));
- llvm_unreachable("unimplemented instruction case");
- }
- }
- }
- #ifndef NDEBUG
- DEBUG(dbgs() << "States after initialization:\n");
- for (auto Pair : States) {
- DEBUG(dbgs() << " " << Pair.second << " for " << *Pair.first << "\n");
- }
- #endif
- // Return a phi state for a base defining value. We'll generate a new
- // base state for known bases and expect to find a cached state otherwise.
- auto getStateForBDV = [&](Value *baseValue) {
- if (isKnownBaseResult(baseValue))
- return BDVState(baseValue);
- auto I = States.find(baseValue);
- assert(I != States.end() && "lookup failed!");
- return I->second;
- };
- bool progress = true;
- while (progress) {
- #ifndef NDEBUG
- const size_t oldSize = States.size();
- #endif
- progress = false;
- // We're only changing values in this loop, thus safe to keep iterators.
- // Since this is computing a fixed point, the order of visit does not
- // effect the result. TODO: We could use a worklist here and make this run
- // much faster.
- for (auto Pair : States) {
- Value *BDV = Pair.first;
- assert(!isKnownBaseResult(BDV) && "why did it get added?");
- // Given an input value for the current instruction, return a BDVState
- // instance which represents the BDV of that value.
- auto getStateForInput = [&](Value *V) mutable {
- Value *BDV = findBaseOrBDV(V, cache);
- return getStateForBDV(BDV);
- };
- MeetBDVStates calculateMeet;
- if (SelectInst *select = dyn_cast<SelectInst>(BDV)) {
- calculateMeet.meetWith(getStateForInput(select->getTrueValue()));
- calculateMeet.meetWith(getStateForInput(select->getFalseValue()));
- } else if (PHINode *Phi = dyn_cast<PHINode>(BDV)) {
- for (Value *Val : Phi->incoming_values())
- calculateMeet.meetWith(getStateForInput(Val));
- } else if (auto *EE = dyn_cast<ExtractElementInst>(BDV)) {
- // The 'meet' for an extractelement is slightly trivial, but it's still
- // useful in that it drives us to conflict if our input is.
- calculateMeet.meetWith(getStateForInput(EE->getVectorOperand()));
- } else {
- // Given there's a inherent type mismatch between the operands, will
- // *always* produce Conflict.
- auto *IE = cast<InsertElementInst>(BDV);
- calculateMeet.meetWith(getStateForInput(IE->getOperand(0)));
- calculateMeet.meetWith(getStateForInput(IE->getOperand(1)));
- }
- BDVState oldState = States[BDV];
- BDVState newState = calculateMeet.getResult();
- if (oldState != newState) {
- progress = true;
- States[BDV] = newState;
- }
- }
- assert(oldSize == States.size() &&
- "fixed point shouldn't be adding any new nodes to state");
- }
- #ifndef NDEBUG
- DEBUG(dbgs() << "States after meet iteration:\n");
- for (auto Pair : States) {
- DEBUG(dbgs() << " " << Pair.second << " for " << *Pair.first << "\n");
- }
- #endif
-
- // Insert Phis for all conflicts
- // TODO: adjust naming patterns to avoid this order of iteration dependency
- for (auto Pair : States) {
- Instruction *I = cast<Instruction>(Pair.first);
- BDVState State = Pair.second;
- assert(!isKnownBaseResult(I) && "why did it get added?");
- assert(!State.isUnknown() && "Optimistic algorithm didn't complete!");
- // extractelement instructions are a bit special in that we may need to
- // insert an extract even when we know an exact base for the instruction.
- // The problem is that we need to convert from a vector base to a scalar
- // base for the particular indice we're interested in.
- if (State.isBase() && isa<ExtractElementInst>(I) &&
- isa<VectorType>(State.getBase()->getType())) {
- auto *EE = cast<ExtractElementInst>(I);
- // TODO: In many cases, the new instruction is just EE itself. We should
- // exploit this, but can't do it here since it would break the invariant
- // about the BDV not being known to be a base.
- auto *BaseInst = ExtractElementInst::Create(State.getBase(),
- EE->getIndexOperand(),
- "base_ee", EE);
- BaseInst->setMetadata("is_base_value", MDNode::get(I->getContext(), {}));
- States[I] = BDVState(BDVState::Base, BaseInst);
- }
- // Since we're joining a vector and scalar base, they can never be the
- // same. As a result, we should always see insert element having reached
- // the conflict state.
- if (isa<InsertElementInst>(I)) {
- assert(State.isConflict());
- }
-
- if (!State.isConflict())
- continue;
- /// Create and insert a new instruction which will represent the base of
- /// the given instruction 'I'.
- auto MakeBaseInstPlaceholder = [](Instruction *I) -> Instruction* {
- if (isa<PHINode>(I)) {
- BasicBlock *BB = I->getParent();
- int NumPreds = std::distance(pred_begin(BB), pred_end(BB));
- assert(NumPreds > 0 && "how did we reach here");
- std::string Name = suffixed_name_or(I, ".base", "base_phi");
- return PHINode::Create(I->getType(), NumPreds, Name, I);
- } else if (SelectInst *Sel = dyn_cast<SelectInst>(I)) {
- // The undef will be replaced later
- UndefValue *Undef = UndefValue::get(Sel->getType());
- std::string Name = suffixed_name_or(I, ".base", "base_select");
- return SelectInst::Create(Sel->getCondition(), Undef,
- Undef, Name, Sel);
- } else if (auto *EE = dyn_cast<ExtractElementInst>(I)) {
- UndefValue *Undef = UndefValue::get(EE->getVectorOperand()->getType());
- std::string Name = suffixed_name_or(I, ".base", "base_ee");
- return ExtractElementInst::Create(Undef, EE->getIndexOperand(), Name,
- EE);
- } else {
- auto *IE = cast<InsertElementInst>(I);
- UndefValue *VecUndef = UndefValue::get(IE->getOperand(0)->getType());
- UndefValue *ScalarUndef = UndefValue::get(IE->getOperand(1)->getType());
- std::string Name = suffixed_name_or(I, ".base", "base_ie");
- return InsertElementInst::Create(VecUndef, ScalarUndef,
- IE->getOperand(2), Name, IE);
- }
- };
- Instruction *BaseInst = MakeBaseInstPlaceholder(I);
- // Add metadata marking this as a base value
- BaseInst->setMetadata("is_base_value", MDNode::get(I->getContext(), {}));
- States[I] = BDVState(BDVState::Conflict, BaseInst);
- }
- // Returns a instruction which produces the base pointer for a given
- // instruction. The instruction is assumed to be an input to one of the BDVs
- // seen in the inference algorithm above. As such, we must either already
- // know it's base defining value is a base, or have inserted a new
- // instruction to propagate the base of it's BDV and have entered that newly
- // introduced instruction into the state table. In either case, we are
- // assured to be able to determine an instruction which produces it's base
- // pointer.
- auto getBaseForInput = [&](Value *Input, Instruction *InsertPt) {
- Value *BDV = findBaseOrBDV(Input, cache);
- Value *Base = nullptr;
- if (isKnownBaseResult(BDV)) {
- Base = BDV;
- } else {
- // Either conflict or base.
- assert(States.count(BDV));
- Base = States[BDV].getBase();
- }
- assert(Base && "can't be null");
- // The cast is needed since base traversal may strip away bitcasts
- if (Base->getType() != Input->getType() &&
- InsertPt) {
- Base = new BitCastInst(Base, Input->getType(), "cast",
- InsertPt);
- }
- return Base;
- };
- // Fixup all the inputs of the new PHIs. Visit order needs to be
- // deterministic and predictable because we're naming newly created
- // instructions.
- for (auto Pair : States) {
- Instruction *BDV = cast<Instruction>(Pair.first);
- BDVState State = Pair.second;
- assert(!isKnownBaseResult(BDV) && "why did it get added?");
- assert(!State.isUnknown() && "Optimistic algorithm didn't complete!");
- if (!State.isConflict())
- continue;
- if (PHINode *basephi = dyn_cast<PHINode>(State.getBase())) {
- PHINode *phi = cast<PHINode>(BDV);
- unsigned NumPHIValues = phi->getNumIncomingValues();
- for (unsigned i = 0; i < NumPHIValues; i++) {
- Value *InVal = phi->getIncomingValue(i);
- BasicBlock *InBB = phi->getIncomingBlock(i);
- // If we've already seen InBB, add the same incoming value
- // we added for it earlier. The IR verifier requires phi
- // nodes with multiple entries from the same basic block
- // to have the same incoming value for each of those
- // entries. If we don't do this check here and basephi
- // has a different type than base, we'll end up adding two
- // bitcasts (and hence two distinct values) as incoming
- // values for the same basic block.
- int blockIndex = basephi->getBasicBlockIndex(InBB);
- if (blockIndex != -1) {
- Value *oldBase = basephi->getIncomingValue(blockIndex);
- basephi->addIncoming(oldBase, InBB);
-
- #ifndef NDEBUG
- Value *Base = getBaseForInput(InVal, nullptr);
- // In essence this assert states: the only way two
- // values incoming from the same basic block may be
- // different is by being different bitcasts of the same
- // value. A cleanup that remains TODO is changing
- // findBaseOrBDV to return an llvm::Value of the correct
- // type (and still remain pure). This will remove the
- // need to add bitcasts.
- assert(Base->stripPointerCasts() == oldBase->stripPointerCasts() &&
- "sanity -- findBaseOrBDV should be pure!");
- #endif
- continue;
- }
- // Find the instruction which produces the base for each input. We may
- // need to insert a bitcast in the incoming block.
- // TODO: Need to split critical edges if insertion is needed
- Value *Base = getBaseForInput(InVal, InBB->getTerminator());
- basephi->addIncoming(Base, InBB);
- }
- assert(basephi->getNumIncomingValues() == NumPHIValues);
- } else if (SelectInst *BaseSel = dyn_cast<SelectInst>(State.getBase())) {
- SelectInst *Sel = cast<SelectInst>(BDV);
- // Operand 1 & 2 are true, false path respectively. TODO: refactor to
- // something more safe and less hacky.
- for (int i = 1; i <= 2; i++) {
- Value *InVal = Sel->getOperand(i);
- // Find the instruction which produces the base for each input. We may
- // need to insert a bitcast.
- Value *Base = getBaseForInput(InVal, BaseSel);
- BaseSel->setOperand(i, Base);
- }
- } else if (auto *BaseEE = dyn_cast<ExtractElementInst>(State.getBase())) {
- Value *InVal = cast<ExtractElementInst>(BDV)->getVectorOperand();
- // Find the instruction which produces the base for each input. We may
- // need to insert a bitcast.
- Value *Base = getBaseForInput(InVal, BaseEE);
- BaseEE->setOperand(0, Base);
- } else {
- auto *BaseIE = cast<InsertElementInst>(State.getBase());
- auto *BdvIE = cast<InsertElementInst>(BDV);
- auto UpdateOperand = [&](int OperandIdx) {
- Value *InVal = BdvIE->getOperand(OperandIdx);
- Value *Base = getBaseForInput(InVal, BaseIE);
- BaseIE->setOperand(OperandIdx, Base);
- };
- UpdateOperand(0); // vector operand
- UpdateOperand(1); // scalar operand
- }
- }
- // Now that we're done with the algorithm, see if we can optimize the
- // results slightly by reducing the number of new instructions needed.
- // Arguably, this should be integrated into the algorithm above, but
- // doing as a post process step is easier to reason about for the moment.
- DenseMap<Value *, Value *> ReverseMap;
- SmallPtrSet<Instruction *, 16> NewInsts;
- SmallSetVector<AssertingVH<Instruction>, 16> Worklist;
- // Note: We need to visit the states in a deterministic order. We uses the
- // Keys we sorted above for this purpose. Note that we are papering over a
- // bigger problem with the algorithm above - it's visit order is not
- // deterministic. A larger change is needed to fix this.
- for (auto Pair : States) {
- auto *BDV = Pair.first;
- auto State = Pair.second;
- Value *Base = State.getBase();
- assert(BDV && Base);
- assert(!isKnownBaseResult(BDV) && "why did it get added?");
- assert(isKnownBaseResult(Base) &&
- "must be something we 'know' is a base pointer");
- if (!State.isConflict())
- continue;
- ReverseMap[Base] = BDV;
- if (auto *BaseI = dyn_cast<Instruction>(Base)) {
- NewInsts.insert(BaseI);
- Worklist.insert(BaseI);
- }
- }
- auto ReplaceBaseInstWith = [&](Value *BDV, Instruction *BaseI,
- Value *Replacement) {
- // Add users which are new instructions (excluding self references)
- for (User *U : BaseI->users())
- if (auto *UI = dyn_cast<Instruction>(U))
- if (NewInsts.count(UI) && UI != BaseI)
- Worklist.insert(UI);
- // Then do the actual replacement
- NewInsts.erase(BaseI);
- ReverseMap.erase(BaseI);
- BaseI->replaceAllUsesWith(Replacement);
- assert(States.count(BDV));
- assert(States[BDV].isConflict() && States[BDV].getBase() == BaseI);
- States[BDV] = BDVState(BDVState::Conflict, Replacement);
- BaseI->eraseFromParent();
- };
- const DataLayout &DL = cast<Instruction>(def)->getModule()->getDataLayout();
- while (!Worklist.empty()) {
- Instruction *BaseI = Worklist.pop_back_val();
- assert(NewInsts.count(BaseI));
- Value *Bdv = ReverseMap[BaseI];
- if (auto *BdvI = dyn_cast<Instruction>(Bdv))
- if (BaseI->isIdenticalTo(BdvI)) {
- DEBUG(dbgs() << "Identical Base: " << *BaseI << "\n");
- ReplaceBaseInstWith(Bdv, BaseI, Bdv);
- continue;
- }
- if (Value *V = SimplifyInstruction(BaseI, DL)) {
- DEBUG(dbgs() << "Base " << *BaseI << " simplified to " << *V << "\n");
- ReplaceBaseInstWith(Bdv, BaseI, V);
- continue;
- }
- }
- // Cache all of our results so we can cheaply reuse them
- // NOTE: This is actually two caches: one of the base defining value
- // relation and one of the base pointer relation! FIXME
- for (auto Pair : States) {
- auto *BDV = Pair.first;
- Value *base = Pair.second.getBase();
- assert(BDV && base);
- std::string fromstr = cache.count(BDV) ? cache[BDV]->getName() : "none";
- DEBUG(dbgs() << "Updating base value cache"
- << " for: " << BDV->getName()
- << " from: " << fromstr
- << " to: " << base->getName() << "\n");
- if (cache.count(BDV)) {
- // Once we transition from the BDV relation being store in the cache to
- // the base relation being stored, it must be stable
- assert((!isKnownBaseResult(cache[BDV]) || cache[BDV] == base) &&
- "base relation should be stable");
- }
- cache[BDV] = base;
- }
- assert(cache.count(def));
- return cache[def];
- }
- // For a set of live pointers (base and/or derived), identify the base
- // pointer of the object which they are derived from. This routine will
- // mutate the IR graph as needed to make the 'base' pointer live at the
- // definition site of 'derived'. This ensures that any use of 'derived' can
- // also use 'base'. This may involve the insertion of a number of
- // additional PHI nodes.
- //
- // preconditions: live is a set of pointer type Values
- //
- // side effects: may insert PHI nodes into the existing CFG, will preserve
- // CFG, will not remove or mutate any existing nodes
- //
- // post condition: PointerToBase contains one (derived, base) pair for every
- // pointer in live. Note that derived can be equal to base if the original
- // pointer was a base pointer.
- static void
- findBasePointers(const StatepointLiveSetTy &live,
- DenseMap<Value *, Value *> &PointerToBase,
- DominatorTree *DT, DefiningValueMapTy &DVCache) {
- // For the naming of values inserted to be deterministic - which makes for
- // much cleaner and more stable tests - we need to assign an order to the
- // live values. DenseSets do not provide a deterministic order across runs.
- SmallVector<Value *, 64> Temp;
- Temp.insert(Temp.end(), live.begin(), live.end());
- std::sort(Temp.begin(), Temp.end(), order_by_name);
- for (Value *ptr : Temp) {
- Value *base = findBasePointer(ptr, DVCache);
- assert(base && "failed to find base pointer");
- PointerToBase[ptr] = base;
- assert((!isa<Instruction>(base) || !isa<Instruction>(ptr) ||
- DT->dominates(cast<Instruction>(base)->getParent(),
- cast<Instruction>(ptr)->getParent())) &&
- "The base we found better dominate the derived pointer");
- // If you see this trip and like to live really dangerously, the code should
- // be correct, just with idioms the verifier can't handle. You can try
- // disabling the verifier at your own substantial risk.
- assert(!isa<ConstantPointerNull>(base) &&
- "the relocation code needs adjustment to handle the relocation of "
- "a null pointer constant without causing false positives in the "
- "safepoint ir verifier.");
- }
- }
- /// Find the required based pointers (and adjust the live set) for the given
- /// parse point.
- static void findBasePointers(DominatorTree &DT, DefiningValueMapTy &DVCache,
- const CallSite &CS,
- PartiallyConstructedSafepointRecord &result) {
- DenseMap<Value *, Value *> PointerToBase;
- findBasePointers(result.LiveSet, PointerToBase, &DT, DVCache);
- if (PrintBasePointers) {
- // Note: Need to print these in a stable order since this is checked in
- // some tests.
- errs() << "Base Pairs (w/o Relocation):\n";
- SmallVector<Value *, 64> Temp;
- Temp.reserve(PointerToBase.size());
- for (auto Pair : PointerToBase) {
- Temp.push_back(Pair.first);
- }
- std::sort(Temp.begin(), Temp.end(), order_by_name);
- for (Value *Ptr : Temp) {
- Value *Base = PointerToBase[Ptr];
- errs() << " derived ";
- Ptr->printAsOperand(errs(), false);
- errs() << " base ";
- Base->printAsOperand(errs(), false);
- errs() << "\n";;
- }
- }
- result.PointerToBase = PointerToBase;
- }
- /// Given an updated version of the dataflow liveness results, update the
- /// liveset and base pointer maps for the call site CS.
- static void recomputeLiveInValues(GCPtrLivenessData &RevisedLivenessData,
- const CallSite &CS,
- PartiallyConstructedSafepointRecord &result);
- static void recomputeLiveInValues(
- Function &F, DominatorTree &DT, ArrayRef<CallSite> toUpdate,
- MutableArrayRef<struct PartiallyConstructedSafepointRecord> records) {
- // TODO-PERF: reuse the original liveness, then simply run the dataflow
- // again. The old values are still live and will help it stabilize quickly.
- GCPtrLivenessData RevisedLivenessData;
- computeLiveInValues(DT, F, RevisedLivenessData);
- for (size_t i = 0; i < records.size(); i++) {
- struct PartiallyConstructedSafepointRecord &info = records[i];
- const CallSite &CS = toUpdate[i];
- recomputeLiveInValues(RevisedLivenessData, CS, info);
- }
- }
- // When inserting gc.relocate and gc.result calls, we need to ensure there are
- // no uses of the original value / return value between the gc.statepoint and
- // the gc.relocate / gc.result call. One case which can arise is a phi node
- // starting one of the successor blocks. We also need to be able to insert the
- // gc.relocates only on the path which goes through the statepoint. We might
- // need to split an edge to make this possible.
- static BasicBlock *
- normalizeForInvokeSafepoint(BasicBlock *BB, BasicBlock *InvokeParent,
- DominatorTree &DT) {
- BasicBlock *Ret = BB;
- if (!BB->getUniquePredecessor())
- Ret = SplitBlockPredecessors(BB, InvokeParent, "", &DT);
- // Now that 'Ret' has unique predecessor we can safely remove all phi nodes
- // from it
- FoldSingleEntryPHINodes(Ret);
- assert(!isa<PHINode>(Ret->begin()) &&
- "All PHI nodes should have been removed!");
- // At this point, we can safely insert a gc.relocate or gc.result as the first
- // instruction in Ret if needed.
- return Ret;
- }
- // Create new attribute set containing only attributes which can be transferred
- // from original call to the safepoint.
- static AttributeSet legalizeCallAttributes(AttributeSet AS) {
- AttributeSet Ret;
- for (unsigned Slot = 0; Slot < AS.getNumSlots(); Slot++) {
- unsigned Index = AS.getSlotIndex(Slot);
- if (Index == AttributeSet::ReturnIndex ||
- Index == AttributeSet::FunctionIndex) {
- for (Attribute Attr : make_range(AS.begin(Slot), AS.end(Slot))) {
- // Do not allow certain attributes - just skip them
- // Safepoint can not be read only or read none.
- if (Attr.hasAttribute(Attribute::ReadNone) ||
- Attr.hasAttribute(Attribute::ReadOnly))
- continue;
- // These attributes control the generation of the gc.statepoint call /
- // invoke itself; and once the gc.statepoint is in place, they're of no
- // use.
- if (Attr.hasAttribute("statepoint-num-patch-bytes") ||
- Attr.hasAttribute("statepoint-id"))
- continue;
- Ret = Ret.addAttributes(
- AS.getContext(), Index,
- AttributeSet::get(AS.getContext(), Index, AttrBuilder(Attr)));
- }
- }
- // Just skip parameter attributes for now
- }
- return Ret;
- }
- /// Helper function to place all gc relocates necessary for the given
- /// statepoint.
- /// Inputs:
- /// liveVariables - list of variables to be relocated.
- /// liveStart - index of the first live variable.
- /// basePtrs - base pointers.
- /// statepointToken - statepoint instruction to which relocates should be
- /// bound.
- /// Builder - Llvm IR builder to be used to construct new calls.
- static void CreateGCRelocates(ArrayRef<Value *> LiveVariables,
- const int LiveStart,
- ArrayRef<Value *> BasePtrs,
- Instruction *StatepointToken,
- IRBuilder<> Builder) {
- if (LiveVariables.empty())
- return;
- auto FindIndex = [](ArrayRef<Value *> LiveVec, Value *Val) {
- auto ValIt = std::find(LiveVec.begin(), LiveVec.end(), Val);
- assert(ValIt != LiveVec.end() && "Val not found in LiveVec!");
- size_t Index = std::distance(LiveVec.begin(), ValIt);
- assert(Index < LiveVec.size() && "Bug in std::find?");
- return Index;
- };
- Module *M = StatepointToken->getModule();
-
- // All gc_relocate are generated as i8 addrspace(1)* (or a vector type whose
- // element type is i8 addrspace(1)*). We originally generated unique
- // declarations for each pointer type, but this proved problematic because
- // the intrinsic mangling code is incomplete and fragile. Since we're moving
- // towards a single unified pointer type anyways, we can just cast everything
- // to an i8* of the right address space. A bitcast is added later to convert
- // gc_relocate to the actual value's type.
- auto getGCRelocateDecl = [&] (Type *Ty) {
- assert(isHandledGCPointerType(Ty));
- auto AS = Ty->getScalarType()->getPointerAddressSpace();
- Type *NewTy = Type::getInt8PtrTy(M->getContext(), AS);
- if (auto *VT = dyn_cast<VectorType>(Ty))
- NewTy = VectorType::get(NewTy, VT->getNumElements());
- return Intrinsic::getDeclaration(M, Intrinsic::experimental_gc_relocate,
- {NewTy});
- };
- // Lazily populated map from input types to the canonicalized form mentioned
- // in the comment above. This should probably be cached somewhere more
- // broadly.
- DenseMap<Type*, Value*> TypeToDeclMap;
- for (unsigned i = 0; i < LiveVariables.size(); i++) {
- // Generate the gc.relocate call and save the result
- Value *BaseIdx =
- Builder.getInt32(LiveStart + FindIndex(LiveVariables, BasePtrs[i]));
- Value *LiveIdx = Builder.getInt32(LiveStart + i);
- Type *Ty = LiveVariables[i]->getType();
- if (!TypeToDeclMap.count(Ty))
- TypeToDeclMap[Ty] = getGCRelocateDecl(Ty);
- Value *GCRelocateDecl = TypeToDeclMap[Ty];
- // only specify a debug name if we can give a useful one
- CallInst *Reloc = Builder.CreateCall(
- GCRelocateDecl, {StatepointToken, BaseIdx, LiveIdx},
- suffixed_name_or(LiveVariables[i], ".relocated", ""));
- // Trick CodeGen into thinking there are lots of free registers at this
- // fake call.
- Reloc->setCallingConv(CallingConv::Cold);
- }
- }
- namespace {
- /// This struct is used to defer RAUWs and `eraseFromParent` s. Using this
- /// avoids having to worry about keeping around dangling pointers to Values.
- class DeferredReplacement {
- AssertingVH<Instruction> Old;
- AssertingVH<Instruction> New;
- public:
- explicit DeferredReplacement(Instruction *Old, Instruction *New) :
- Old(Old), New(New) {
- assert(Old != New && "Not allowed!");
- }
- /// Does the task represented by this instance.
- void doReplacement() {
- Instruction *OldI = Old;
- Instruction *NewI = New;
- assert(OldI != NewI && "Disallowed at construction?!");
- Old = nullptr;
- New = nullptr;
- if (NewI)
- OldI->replaceAllUsesWith(NewI);
- OldI->eraseFromParent();
- }
- };
- }
- static void
- makeStatepointExplicitImpl(const CallSite CS, /* to replace */
- const SmallVectorImpl<Value *> &BasePtrs,
- const SmallVectorImpl<Value *> &LiveVariables,
- PartiallyConstructedSafepointRecord &Result,
- std::vector<DeferredReplacement> &Replacements) {
- assert(BasePtrs.size() == LiveVariables.size());
- assert((UseDeoptBundles || isStatepoint(CS)) &&
- "This method expects to be rewriting a statepoint");
- // Then go ahead and use the builder do actually do the inserts. We insert
- // immediately before the previous instruction under the assumption that all
- // arguments will be available here. We can't insert afterwards since we may
- // be replacing a terminator.
- Instruction *InsertBefore = CS.getInstruction();
- IRBuilder<> Builder(InsertBefore);
- ArrayRef<Value *> GCArgs(LiveVariables);
- uint64_t StatepointID = 0xABCDEF00;
- uint32_t NumPatchBytes = 0;
- uint32_t Flags = uint32_t(StatepointFlags::None);
- ArrayRef<Use> CallArgs;
- ArrayRef<Use> DeoptArgs;
- ArrayRef<Use> TransitionArgs;
- Value *CallTarget = nullptr;
- if (UseDeoptBundles) {
- CallArgs = {CS.arg_begin(), CS.arg_end()};
- DeoptArgs = GetDeoptBundleOperands(CS);
- // TODO: we don't fill in TransitionArgs or Flags in this branch, but we
- // could have an operand bundle for that too.
- AttributeSet OriginalAttrs = CS.getAttributes();
- Attribute AttrID = OriginalAttrs.getAttribute(AttributeSet::FunctionIndex,
- "statepoint-id");
- if (AttrID.isStringAttribute())
- AttrID.getValueAsString().getAsInteger(10, StatepointID);
- Attribute AttrNumPatchBytes = OriginalAttrs.getAttribute(
- AttributeSet::FunctionIndex, "statepoint-num-patch-bytes");
- if (AttrNumPatchBytes.isStringAttribute())
- AttrNumPatchBytes.getValueAsString().getAsInteger(10, NumPatchBytes);
- CallTarget = CS.getCalledValue();
- } else {
- // This branch will be gone soon, and we will soon only support the
- // UseDeoptBundles == true configuration.
- Statepoint OldSP(CS);
- StatepointID = OldSP.getID();
- NumPatchBytes = OldSP.getNumPatchBytes();
- Flags = OldSP.getFlags();
- CallArgs = {OldSP.arg_begin(), OldSP.arg_end()};
- DeoptArgs = {OldSP.vm_state_begin(), OldSP.vm_state_end()};
- TransitionArgs = {OldSP.gc_transition_args_begin(),
- OldSP.gc_transition_args_end()};
- CallTarget = OldSP.getCalledValue();
- }
- // Create the statepoint given all the arguments
- Instruction *Token = nullptr;
- AttributeSet ReturnAttrs;
- if (CS.isCall()) {
- CallInst *ToReplace = cast<CallInst>(CS.getInstruction());
- CallInst *Call = Builder.CreateGCStatepointCall(
- StatepointID, NumPatchBytes, CallTarget, Flags, CallArgs,
- TransitionArgs, DeoptArgs, GCArgs, "safepoint_token");
- Call->setTailCall(ToReplace->isTailCall());
- Call->setCallingConv(ToReplace->getCallingConv());
- // Currently we will fail on parameter attributes and on certain
- // function attributes.
- AttributeSet NewAttrs = legalizeCallAttributes(ToReplace->getAttributes());
- // In case if we can handle this set of attributes - set up function attrs
- // directly on statepoint and return attrs later for gc_result intrinsic.
- Call->setAttributes(NewAttrs.getFnAttributes());
- ReturnAttrs = NewAttrs.getRetAttributes();
- Token = Call;
- // Put the following gc_result and gc_relocate calls immediately after the
- // the old call (which we're about to delete)
- assert(ToReplace->getNextNode() && "Not a terminator, must have next!");
- Builder.SetInsertPoint(ToReplace->getNextNode());
- Builder.SetCurrentDebugLocation(ToReplace->getNextNode()->getDebugLoc());
- } else {
- InvokeInst *ToReplace = cast<InvokeInst>(CS.getInstruction());
- // Insert the new invoke into the old block. We'll remove the old one in a
- // moment at which point this will become the new terminator for the
- // original block.
- InvokeInst *Invoke = Builder.CreateGCStatepointInvoke(
- StatepointID, NumPatchBytes, CallTarget, ToReplace->getNormalDest(),
- ToReplace->getUnwindDest(), Flags, CallArgs, TransitionArgs, DeoptArgs,
- GCArgs, "statepoint_token");
- Invoke->setCallingConv(ToReplace->getCallingConv());
- // Currently we will fail on parameter attributes and on certain
- // function attributes.
- AttributeSet NewAttrs = legalizeCallAttributes(ToReplace->getAttributes());
- // In case if we can handle this set of attributes - set up function attrs
- // directly on statepoint and return attrs later for gc_result intrinsic.
- Invoke->setAttributes(NewAttrs.getFnAttributes());
- ReturnAttrs = NewAttrs.getRetAttributes();
- Token = Invoke;
- // Generate gc relocates in exceptional path
- BasicBlock *UnwindBlock = ToReplace->getUnwindDest();
- assert(!isa<PHINode>(UnwindBlock->begin()) &&
- UnwindBlock->getUniquePredecessor() &&
- "can't safely insert in this block!");
- Builder.SetInsertPoint(&*UnwindBlock->getFirstInsertionPt());
- Builder.SetCurrentDebugLocation(ToReplace->getDebugLoc());
- // Attach exceptional gc relocates to the landingpad.
- Instruction *ExceptionalToken = UnwindBlock->getLandingPadInst();
- Result.UnwindToken = ExceptionalToken;
- const unsigned LiveStartIdx = Statepoint(Token).gcArgsStartIdx();
- CreateGCRelocates(LiveVariables, LiveStartIdx, BasePtrs, ExceptionalToken,
- Builder);
- // Generate gc relocates and returns for normal block
- BasicBlock *NormalDest = ToReplace->getNormalDest();
- assert(!isa<PHINode>(NormalDest->begin()) &&
- NormalDest->getUniquePredecessor() &&
- "can't safely insert in this block!");
- Builder.SetInsertPoint(&*NormalDest->getFirstInsertionPt());
- // gc relocates will be generated later as if it were regular call
- // statepoint
- }
- assert(Token && "Should be set in one of the above branches!");
- if (UseDeoptBundles) {
- Token->setName("statepoint_token");
- if (!CS.getType()->isVoidTy() && !CS.getInstruction()->use_empty()) {
- StringRef Name =
- CS.getInstruction()->hasName() ? CS.getInstruction()->getName() : "";
- CallInst *GCResult = Builder.CreateGCResult(Token, CS.getType(), Name);
- GCResult->setAttributes(CS.getAttributes().getRetAttributes());
- // We cannot RAUW or delete CS.getInstruction() because it could be in the
- // live set of some other safepoint, in which case that safepoint's
- // PartiallyConstructedSafepointRecord will hold a raw pointer to this
- // llvm::Instruction. Instead, we defer the replacement and deletion to
- // after the live sets have been made explicit in the IR, and we no longer
- // have raw pointers to worry about.
- Replacements.emplace_back(CS.getInstruction(), GCResult);
- } else {
- Replacements.emplace_back(CS.getInstruction(), nullptr);
- }
- } else {
- assert(!CS.getInstruction()->hasNUsesOrMore(2) &&
- "only valid use before rewrite is gc.result");
- assert(!CS.getInstruction()->hasOneUse() ||
- isGCResult(cast<Instruction>(*CS.getInstruction()->user_begin())));
- // Take the name of the original statepoint token if there was one.
- Token->takeName(CS.getInstruction());
- // Update the gc.result of the original statepoint (if any) to use the newly
- // inserted statepoint. This is safe to do here since the token can't be
- // considered a live reference.
- CS.getInstruction()->replaceAllUsesWith(Token);
- CS.getInstruction()->eraseFromParent();
- }
- Result.StatepointToken = Token;
- // Second, create a gc.relocate for every live variable
- const unsigned LiveStartIdx = Statepoint(Token).gcArgsStartIdx();
- CreateGCRelocates(LiveVariables, LiveStartIdx, BasePtrs, Token, Builder);
- }
- namespace {
- struct NameOrdering {
- Value *Base;
- Value *Derived;
- bool operator()(NameOrdering const &a, NameOrdering const &b) {
- return -1 == a.Derived->getName().compare(b.Derived->getName());
- }
- };
- }
- static void StabilizeOrder(SmallVectorImpl<Value *> &BaseVec,
- SmallVectorImpl<Value *> &LiveVec) {
- assert(BaseVec.size() == LiveVec.size());
- SmallVector<NameOrdering, 64> Temp;
- for (size_t i = 0; i < BaseVec.size(); i++) {
- NameOrdering v;
- v.Base = BaseVec[i];
- v.Derived = LiveVec[i];
- Temp.push_back(v);
- }
- std::sort(Temp.begin(), Temp.end(), NameOrdering());
- for (size_t i = 0; i < BaseVec.size(); i++) {
- BaseVec[i] = Temp[i].Base;
- LiveVec[i] = Temp[i].Derived;
- }
- }
- // Replace an existing gc.statepoint with a new one and a set of gc.relocates
- // which make the relocations happening at this safepoint explicit.
- //
- // WARNING: Does not do any fixup to adjust users of the original live
- // values. That's the callers responsibility.
- static void
- makeStatepointExplicit(DominatorTree &DT, const CallSite &CS,
- PartiallyConstructedSafepointRecord &Result,
- std::vector<DeferredReplacement> &Replacements) {
- const auto &LiveSet = Result.LiveSet;
- const auto &PointerToBase = Result.PointerToBase;
- // Convert to vector for efficient cross referencing.
- SmallVector<Value *, 64> BaseVec, LiveVec;
- LiveVec.reserve(LiveSet.size());
- BaseVec.reserve(LiveSet.size());
- for (Value *L : LiveSet) {
- LiveVec.push_back(L);
- assert(PointerToBase.count(L));
- Value *Base = PointerToBase.find(L)->second;
- BaseVec.push_back(Base);
- }
- assert(LiveVec.size() == BaseVec.size());
- // To make the output IR slightly more stable (for use in diffs), ensure a
- // fixed order of the values in the safepoint (by sorting the value name).
- // The order is otherwise meaningless.
- StabilizeOrder(BaseVec, LiveVec);
- // Do the actual rewriting and delete the old statepoint
- makeStatepointExplicitImpl(CS, BaseVec, LiveVec, Result, Replacements);
- }
- // Helper function for the relocationViaAlloca.
- //
- // It receives iterator to the statepoint gc relocates and emits a store to the
- // assigned location (via allocaMap) for the each one of them. It adds the
- // visited values into the visitedLiveValues set, which we will later use them
- // for sanity checking.
- static void
- insertRelocationStores(iterator_range<Value::user_iterator> GCRelocs,
- DenseMap<Value *, Value *> &AllocaMap,
- DenseSet<Value *> &VisitedLiveValues) {
- for (User *U : GCRelocs) {
- GCRelocateInst *Relocate = dyn_cast<GCRelocateInst>(U);
- if (!Relocate)
- continue;
- Value *OriginalValue = const_cast<Value *>(Relocate->getDerivedPtr());
- assert(AllocaMap.count(OriginalValue));
- Value *Alloca = AllocaMap[OriginalValue];
- // Emit store into the related alloca
- // All gc_relocates are i8 addrspace(1)* typed, and it must be bitcasted to
- // the correct type according to alloca.
- assert(Relocate->getNextNode() &&
- "Should always have one since it's not a terminator");
- IRBuilder<> Builder(Relocate->getNextNode());
- Value *CastedRelocatedValue =
- Builder.CreateBitCast(Relocate,
- cast<AllocaInst>(Alloca)->getAllocatedType(),
- suffixed_name_or(Relocate, ".casted", ""));
- StoreInst *Store = new StoreInst(CastedRelocatedValue, Alloca);
- Store->insertAfter(cast<Instruction>(CastedRelocatedValue));
- #ifndef NDEBUG
- VisitedLiveValues.insert(OriginalValue);
- #endif
- }
- }
- // Helper function for the "relocationViaAlloca". Similar to the
- // "insertRelocationStores" but works for rematerialized values.
- static void
- insertRematerializationStores(
- RematerializedValueMapTy RematerializedValues,
- DenseMap<Value *, Value *> &AllocaMap,
- DenseSet<Value *> &VisitedLiveValues) {
- for (auto RematerializedValuePair: RematerializedValues) {
- Instruction *RematerializedValue = RematerializedValuePair.first;
- Value *OriginalValue = RematerializedValuePair.second;
- assert(AllocaMap.count(OriginalValue) &&
- "Can not find alloca for rematerialized value");
- Value *Alloca = AllocaMap[OriginalValue];
- StoreInst *Store = new StoreInst(RematerializedValue, Alloca);
- Store->insertAfter(RematerializedValue);
- #ifndef NDEBUG
- VisitedLiveValues.insert(OriginalValue);
- #endif
- }
- }
- /// Do all the relocation update via allocas and mem2reg
- static void relocationViaAlloca(
- Function &F, DominatorTree &DT, ArrayRef<Value *> Live,
- ArrayRef<PartiallyConstructedSafepointRecord> Records) {
- #ifndef NDEBUG
- // record initial number of (static) allocas; we'll check we have the same
- // number when we get done.
- int InitialAllocaNum = 0;
- for (auto I = F.getEntryBlock().begin(), E = F.getEntryBlock().end(); I != E;
- I++)
- if (isa<AllocaInst>(*I))
- InitialAllocaNum++;
- #endif
- // TODO-PERF: change data structures, reserve
- DenseMap<Value *, Value *> AllocaMap;
- SmallVector<AllocaInst *, 200> PromotableAllocas;
- // Used later to chack that we have enough allocas to store all values
- std::size_t NumRematerializedValues = 0;
- PromotableAllocas.reserve(Live.size());
- // Emit alloca for "LiveValue" and record it in "allocaMap" and
- // "PromotableAllocas"
- auto emitAllocaFor = [&](Value *LiveValue) {
- AllocaInst *Alloca = new AllocaInst(LiveValue->getType(), "",
- F.getEntryBlock().getFirstNonPHI());
- AllocaMap[LiveValue] = Alloca;
- PromotableAllocas.push_back(Alloca);
- };
- // Emit alloca for each live gc pointer
- for (Value *V : Live)
- emitAllocaFor(V);
- // Emit allocas for rematerialized values
- for (const auto &Info : Records)
- for (auto RematerializedValuePair : Info.RematerializedValues) {
- Value *OriginalValue = RematerializedValuePair.second;
- if (AllocaMap.count(OriginalValue) != 0)
- continue;
- emitAllocaFor(OriginalValue);
- ++NumRematerializedValues;
- }
- // The next two loops are part of the same conceptual operation. We need to
- // insert a store to the alloca after the original def and at each
- // redefinition. We need to insert a load before each use. These are split
- // into distinct loops for performance reasons.
- // Update gc pointer after each statepoint: either store a relocated value or
- // null (if no relocated value was found for this gc pointer and it is not a
- // gc_result). This must happen before we update the statepoint with load of
- // alloca otherwise we lose the link between statepoint and old def.
- for (const auto &Info : Records) {
- Value *Statepoint = Info.StatepointToken;
- // This will be used for consistency check
- DenseSet<Value *> VisitedLiveValues;
- // Insert stores for normal statepoint gc relocates
- insertRelocationStores(Statepoint->users(), AllocaMap, VisitedLiveValues);
- // In case if it was invoke statepoint
- // we will insert stores for exceptional path gc relocates.
- if (isa<InvokeInst>(Statepoint)) {
- insertRelocationStores(Info.UnwindToken->users(), AllocaMap,
- VisitedLiveValues);
- }
- // Do similar thing with rematerialized values
- insertRematerializationStores(Info.RematerializedValues, AllocaMap,
- VisitedLiveValues);
- if (ClobberNonLive) {
- // As a debugging aid, pretend that an unrelocated pointer becomes null at
- // the gc.statepoint. This will turn some subtle GC problems into
- // slightly easier to debug SEGVs. Note that on large IR files with
- // lots of gc.statepoints this is extremely costly both memory and time
- // wise.
- SmallVector<AllocaInst *, 64> ToClobber;
- for (auto Pair : AllocaMap) {
- Value *Def = Pair.first;
- AllocaInst *Alloca = cast<AllocaInst>(Pair.second);
- // This value was relocated
- if (VisitedLiveValues.count(Def)) {
- continue;
- }
- ToClobber.push_back(Alloca);
- }
- auto InsertClobbersAt = [&](Instruction *IP) {
- for (auto *AI : ToClobber) {
- auto PT = cast<PointerType>(AI->getAllocatedType());
- Constant *CPN = ConstantPointerNull::get(PT);
- StoreInst *Store = new StoreInst(CPN, AI);
- Store->insertBefore(IP);
- }
- };
- // Insert the clobbering stores. These may get intermixed with the
- // gc.results and gc.relocates, but that's fine.
- if (auto II = dyn_cast<InvokeInst>(Statepoint)) {
- InsertClobbersAt(&*II->getNormalDest()->getFirstInsertionPt());
- InsertClobbersAt(&*II->getUnwindDest()->getFirstInsertionPt());
- } else {
- InsertClobbersAt(cast<Instruction>(Statepoint)->getNextNode());
- }
- }
- }
- // Update use with load allocas and add store for gc_relocated.
- for (auto Pair : AllocaMap) {
- Value *Def = Pair.first;
- Value *Alloca = Pair.second;
- // We pre-record the uses of allocas so that we dont have to worry about
- // later update that changes the user information..
- SmallVector<Instruction *, 20> Uses;
- // PERF: trade a linear scan for repeated reallocation
- Uses.reserve(std::distance(Def->user_begin(), Def->user_end()));
- for (User *U : Def->users()) {
- if (!isa<ConstantExpr>(U)) {
- // If the def has a ConstantExpr use, then the def is either a
- // ConstantExpr use itself or null. In either case
- // (recursively in the first, directly in the second), the oop
- // it is ultimately dependent on is null and this particular
- // use does not need to be fixed up.
- Uses.push_back(cast<Instruction>(U));
- }
- }
- std::sort(Uses.begin(), Uses.end());
- auto Last = std::unique(Uses.begin(), Uses.end());
- Uses.erase(Last, Uses.end());
- for (Instruction *Use : Uses) {
- if (isa<PHINode>(Use)) {
- PHINode *Phi = cast<PHINode>(Use);
- for (unsigned i = 0; i < Phi->getNumIncomingValues(); i++) {
- if (Def == Phi->getIncomingValue(i)) {
- LoadInst *Load = new LoadInst(
- Alloca, "", Phi->getIncomingBlock(i)->getTerminator());
- Phi->setIncomingValue(i, Load);
- }
- }
- } else {
- LoadInst *Load = new LoadInst(Alloca, "", Use);
- Use->replaceUsesOfWith(Def, Load);
- }
- }
- // Emit store for the initial gc value. Store must be inserted after load,
- // otherwise store will be in alloca's use list and an extra load will be
- // inserted before it.
- StoreInst *Store = new StoreInst(Def, Alloca);
- if (Instruction *Inst = dyn_cast<Instruction>(Def)) {
- if (InvokeInst *Invoke = dyn_cast<InvokeInst>(Inst)) {
- // InvokeInst is a TerminatorInst so the store need to be inserted
- // into its normal destination block.
- BasicBlock *NormalDest = Invoke->getNormalDest();
- Store->insertBefore(NormalDest->getFirstNonPHI());
- } else {
- assert(!Inst->isTerminator() &&
- "The only TerminatorInst that can produce a value is "
- "InvokeInst which is handled above.");
- Store->insertAfter(Inst);
- }
- } else {
- assert(isa<Argument>(Def));
- Store->insertAfter(cast<Instruction>(Alloca));
- }
- }
- assert(PromotableAllocas.size() == Live.size() + NumRematerializedValues &&
- "we must have the same allocas with lives");
- if (!PromotableAllocas.empty()) {
- // Apply mem2reg to promote alloca to SSA
- PromoteMemToReg(PromotableAllocas, DT);
- }
- #ifndef NDEBUG
- for (auto &I : F.getEntryBlock())
- if (isa<AllocaInst>(I))
- InitialAllocaNum--;
- assert(InitialAllocaNum == 0 && "We must not introduce any extra allocas");
- #endif
- }
- /// Implement a unique function which doesn't require we sort the input
- /// vector. Doing so has the effect of changing the output of a couple of
- /// tests in ways which make them less useful in testing fused safepoints.
- template <typename T> static void unique_unsorted(SmallVectorImpl<T> &Vec) {
- SmallSet<T, 8> Seen;
- Vec.erase(std::remove_if(Vec.begin(), Vec.end(), [&](const T &V) {
- return !Seen.insert(V).second;
- }), Vec.end());
- }
- /// Insert holders so that each Value is obviously live through the entire
- /// lifetime of the call.
- static void insertUseHolderAfter(CallSite &CS, const ArrayRef<Value *> Values,
- SmallVectorImpl<CallInst *> &Holders) {
- if (Values.empty())
- // No values to hold live, might as well not insert the empty holder
- return;
- Module *M = CS.getInstruction()->getModule();
- // Use a dummy vararg function to actually hold the values live
- Function *Func = cast<Function>(M->getOrInsertFunction(
- "__tmp_use", FunctionType::get(Type::getVoidTy(M->getContext()), true)));
- if (CS.isCall()) {
- // For call safepoints insert dummy calls right after safepoint
- Holders.push_back(CallInst::Create(Func, Values, "",
- &*++CS.getInstruction()->getIterator()));
- return;
- }
- // For invoke safepooints insert dummy calls both in normal and
- // exceptional destination blocks
- auto *II = cast<InvokeInst>(CS.getInstruction());
- Holders.push_back(CallInst::Create(
- Func, Values, "", &*II->getNormalDest()->getFirstInsertionPt()));
- Holders.push_back(CallInst::Create(
- Func, Values, "", &*II->getUnwindDest()->getFirstInsertionPt()));
- }
- static void findLiveReferences(
- Function &F, DominatorTree &DT, ArrayRef<CallSite> toUpdate,
- MutableArrayRef<struct PartiallyConstructedSafepointRecord> records) {
- GCPtrLivenessData OriginalLivenessData;
- computeLiveInValues(DT, F, OriginalLivenessData);
- for (size_t i = 0; i < records.size(); i++) {
- struct PartiallyConstructedSafepointRecord &info = records[i];
- const CallSite &CS = toUpdate[i];
- analyzeParsePointLiveness(DT, OriginalLivenessData, CS, info);
- }
- }
- /// Remove any vector of pointers from the live set by scalarizing them over the
- /// statepoint instruction. Adds the scalarized pieces to the live set. It
- /// would be preferable to include the vector in the statepoint itself, but
- /// the lowering code currently does not handle that. Extending it would be
- /// slightly non-trivial since it requires a format change. Given how rare
- /// such cases are (for the moment?) scalarizing is an acceptable compromise.
- static void splitVectorValues(Instruction *StatepointInst,
- StatepointLiveSetTy &LiveSet,
- DenseMap<Value *, Value *>& PointerToBase,
- DominatorTree &DT) {
- SmallVector<Value *, 16> ToSplit;
- for (Value *V : LiveSet)
- if (isa<VectorType>(V->getType()))
- ToSplit.push_back(V);
- if (ToSplit.empty())
- return;
- DenseMap<Value *, SmallVector<Value *, 16>> ElementMapping;
- Function &F = *(StatepointInst->getParent()->getParent());
- DenseMap<Value *, AllocaInst *> AllocaMap;
- // First is normal return, second is exceptional return (invoke only)
- DenseMap<Value *, std::pair<Value *, Value *>> Replacements;
- for (Value *V : ToSplit) {
- AllocaInst *Alloca =
- new AllocaInst(V->getType(), "", F.getEntryBlock().getFirstNonPHI());
- AllocaMap[V] = Alloca;
- VectorType *VT = cast<VectorType>(V->getType());
- IRBuilder<> Builder(StatepointInst);
- SmallVector<Value *, 16> Elements;
- for (unsigned i = 0; i < VT->getNumElements(); i++)
- Elements.push_back(Builder.CreateExtractElement(V, Builder.getInt32(i)));
- ElementMapping[V] = Elements;
- auto InsertVectorReform = [&](Instruction *IP) {
- Builder.SetInsertPoint(IP);
- Builder.SetCurrentDebugLocation(IP->getDebugLoc());
- Value *ResultVec = UndefValue::get(VT);
- for (unsigned i = 0; i < VT->getNumElements(); i++)
- ResultVec = Builder.CreateInsertElement(ResultVec, Elements[i],
- Builder.getInt32(i));
- return ResultVec;
- };
- if (isa<CallInst>(StatepointInst)) {
- BasicBlock::iterator Next(StatepointInst);
- Next++;
- Instruction *IP = &*(Next);
- Replacements[V].first = InsertVectorReform(IP);
- Replacements[V].second = nullptr;
- } else {
- InvokeInst *Invoke = cast<InvokeInst>(StatepointInst);
- // We've already normalized - check that we don't have shared destination
- // blocks
- BasicBlock *NormalDest = Invoke->getNormalDest();
- assert(!isa<PHINode>(NormalDest->begin()));
- BasicBlock *UnwindDest = Invoke->getUnwindDest();
- assert(!isa<PHINode>(UnwindDest->begin()));
- // Insert insert element sequences in both successors
- Instruction *IP = &*(NormalDest->getFirstInsertionPt());
- Replacements[V].first = InsertVectorReform(IP);
- IP = &*(UnwindDest->getFirstInsertionPt());
- Replacements[V].second = InsertVectorReform(IP);
- }
- }
- for (Value *V : ToSplit) {
- AllocaInst *Alloca = AllocaMap[V];
- // Capture all users before we start mutating use lists
- SmallVector<Instruction *, 16> Users;
- for (User *U : V->users())
- Users.push_back(cast<Instruction>(U));
- for (Instruction *I : Users) {
- if (auto Phi = dyn_cast<PHINode>(I)) {
- for (unsigned i = 0; i < Phi->getNumIncomingValues(); i++)
- if (V == Phi->getIncomingValue(i)) {
- LoadInst *Load = new LoadInst(
- Alloca, "", Phi->getIncomingBlock(i)->getTerminator());
- Phi->setIncomingValue(i, Load);
- }
- } else {
- LoadInst *Load = new LoadInst(Alloca, "", I);
- I->replaceUsesOfWith(V, Load);
- }
- }
- // Store the original value and the replacement value into the alloca
- StoreInst *Store = new StoreInst(V, Alloca);
- if (auto I = dyn_cast<Instruction>(V))
- Store->insertAfter(I);
- else
- Store->insertAfter(Alloca);
- // Normal return for invoke, or call return
- Instruction *Replacement = cast<Instruction>(Replacements[V].first);
- (new StoreInst(Replacement, Alloca))->insertAfter(Replacement);
- // Unwind return for invoke only
- Replacement = cast_or_null<Instruction>(Replacements[V].second);
- if (Replacement)
- (new StoreInst(Replacement, Alloca))->insertAfter(Replacement);
- }
- // apply mem2reg to promote alloca to SSA
- SmallVector<AllocaInst *, 16> Allocas;
- for (Value *V : ToSplit)
- Allocas.push_back(AllocaMap[V]);
- PromoteMemToReg(Allocas, DT);
- // Update our tracking of live pointers and base mappings to account for the
- // changes we just made.
- for (Value *V : ToSplit) {
- auto &Elements = ElementMapping[V];
- LiveSet.erase(V);
- LiveSet.insert(Elements.begin(), Elements.end());
- // We need to update the base mapping as well.
- assert(PointerToBase.count(V));
- Value *OldBase = PointerToBase[V];
- auto &BaseElements = ElementMapping[OldBase];
- PointerToBase.erase(V);
- assert(Elements.size() == BaseElements.size());
- for (unsigned i = 0; i < Elements.size(); i++) {
- Value *Elem = Elements[i];
- PointerToBase[Elem] = BaseElements[i];
- }
- }
- }
- // Helper function for the "rematerializeLiveValues". It walks use chain
- // starting from the "CurrentValue" until it meets "BaseValue". Only "simple"
- // values are visited (currently it is GEP's and casts). Returns true if it
- // successfully reached "BaseValue" and false otherwise.
- // Fills "ChainToBase" array with all visited values. "BaseValue" is not
- // recorded.
- static bool findRematerializableChainToBasePointer(
- SmallVectorImpl<Instruction*> &ChainToBase,
- Value *CurrentValue, Value *BaseValue) {
- // We have found a base value
- if (CurrentValue == BaseValue) {
- return true;
- }
- if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(CurrentValue)) {
- ChainToBase.push_back(GEP);
- return findRematerializableChainToBasePointer(ChainToBase,
- GEP->getPointerOperand(),
- BaseValue);
- }
- if (CastInst *CI = dyn_cast<CastInst>(CurrentValue)) {
- if (!CI->isNoopCast(CI->getModule()->getDataLayout()))
- return false;
- ChainToBase.push_back(CI);
- return findRematerializableChainToBasePointer(ChainToBase,
- CI->getOperand(0), BaseValue);
- }
- // Not supported instruction in the chain
- return false;
- }
- // Helper function for the "rematerializeLiveValues". Compute cost of the use
- // chain we are going to rematerialize.
- static unsigned
- chainToBasePointerCost(SmallVectorImpl<Instruction*> &Chain,
- TargetTransformInfo &TTI) {
- unsigned Cost = 0;
- for (Instruction *Instr : Chain) {
- if (CastInst *CI = dyn_cast<CastInst>(Instr)) {
- assert(CI->isNoopCast(CI->getModule()->getDataLayout()) &&
- "non noop cast is found during rematerialization");
- Type *SrcTy = CI->getOperand(0)->getType();
- Cost += TTI.getCastInstrCost(CI->getOpcode(), CI->getType(), SrcTy);
- } else if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(Instr)) {
- // Cost of the address calculation
- Type *ValTy = GEP->getSourceElementType();
- Cost += TTI.getAddressComputationCost(ValTy);
- // And cost of the GEP itself
- // TODO: Use TTI->getGEPCost here (it exists, but appears to be not
- // allowed for the external usage)
- if (!GEP->hasAllConstantIndices())
- Cost += 2;
- } else {
- llvm_unreachable("unsupported instruciton type during rematerialization");
- }
- }
- return Cost;
- }
- // From the statepoint live set pick values that are cheaper to recompute then
- // to relocate. Remove this values from the live set, rematerialize them after
- // statepoint and record them in "Info" structure. Note that similar to
- // relocated values we don't do any user adjustments here.
- static void rematerializeLiveValues(CallSite CS,
- PartiallyConstructedSafepointRecord &Info,
- TargetTransformInfo &TTI) {
- const unsigned int ChainLengthThreshold = 10;
- // Record values we are going to delete from this statepoint live set.
- // We can not di this in following loop due to iterator invalidation.
- SmallVector<Value *, 32> LiveValuesToBeDeleted;
- for (Value *LiveValue: Info.LiveSet) {
- // For each live pointer find it's defining chain
- SmallVector<Instruction *, 3> ChainToBase;
- assert(Info.PointerToBase.count(LiveValue));
- bool FoundChain =
- findRematerializableChainToBasePointer(ChainToBase,
- LiveValue,
- Info.PointerToBase[LiveValue]);
- // Nothing to do, or chain is too long
- if (!FoundChain ||
- ChainToBase.size() == 0 ||
- ChainToBase.size() > ChainLengthThreshold)
- continue;
- // Compute cost of this chain
- unsigned Cost = chainToBasePointerCost(ChainToBase, TTI);
- // TODO: We can also account for cases when we will be able to remove some
- // of the rematerialized values by later optimization passes. I.e if
- // we rematerialized several intersecting chains. Or if original values
- // don't have any uses besides this statepoint.
- // For invokes we need to rematerialize each chain twice - for normal and
- // for unwind basic blocks. Model this by multiplying cost by two.
- if (CS.isInvoke()) {
- Cost *= 2;
- }
- // If it's too expensive - skip it
- if (Cost >= RematerializationThreshold)
- continue;
- // Remove value from the live set
- LiveValuesToBeDeleted.push_back(LiveValue);
- // Clone instructions and record them inside "Info" structure
- // Walk backwards to visit top-most instructions first
- std::reverse(ChainToBase.begin(), ChainToBase.end());
- // Utility function which clones all instructions from "ChainToBase"
- // and inserts them before "InsertBefore". Returns rematerialized value
- // which should be used after statepoint.
- auto rematerializeChain = [&ChainToBase](Instruction *InsertBefore) {
- Instruction *LastClonedValue = nullptr;
- Instruction *LastValue = nullptr;
- for (Instruction *Instr: ChainToBase) {
- // Only GEP's and casts are suported as we need to be careful to not
- // introduce any new uses of pointers not in the liveset.
- // Note that it's fine to introduce new uses of pointers which were
- // otherwise not used after this statepoint.
- assert(isa<GetElementPtrInst>(Instr) || isa<CastInst>(Instr));
- Instruction *ClonedValue = Instr->clone();
- ClonedValue->insertBefore(InsertBefore);
- ClonedValue->setName(Instr->getName() + ".remat");
- // If it is not first instruction in the chain then it uses previously
- // cloned value. We should update it to use cloned value.
- if (LastClonedValue) {
- assert(LastValue);
- ClonedValue->replaceUsesOfWith(LastValue, LastClonedValue);
- #ifndef NDEBUG
- // Assert that cloned instruction does not use any instructions from
- // this chain other than LastClonedValue
- for (auto OpValue : ClonedValue->operand_values()) {
- assert(std::find(ChainToBase.begin(), ChainToBase.end(), OpValue) ==
- ChainToBase.end() &&
- "incorrect use in rematerialization chain");
- }
- #endif
- }
- LastClonedValue = ClonedValue;
- LastValue = Instr;
- }
- assert(LastClonedValue);
- return LastClonedValue;
- };
- // Different cases for calls and invokes. For invokes we need to clone
- // instructions both on normal and unwind path.
- if (CS.isCall()) {
- Instruction *InsertBefore = CS.getInstruction()->getNextNode();
- assert(InsertBefore);
- Instruction *RematerializedValue = rematerializeChain(InsertBefore);
- Info.RematerializedValues[RematerializedValue] = LiveValue;
- } else {
- InvokeInst *Invoke = cast<InvokeInst>(CS.getInstruction());
- Instruction *NormalInsertBefore =
- &*Invoke->getNormalDest()->getFirstInsertionPt();
- Instruction *UnwindInsertBefore =
- &*Invoke->getUnwindDest()->getFirstInsertionPt();
- Instruction *NormalRematerializedValue =
- rematerializeChain(NormalInsertBefore);
- Instruction *UnwindRematerializedValue =
- rematerializeChain(UnwindInsertBefore);
- Info.RematerializedValues[NormalRematerializedValue] = LiveValue;
- Info.RematerializedValues[UnwindRematerializedValue] = LiveValue;
- }
- }
- // Remove rematerializaed values from the live set
- for (auto LiveValue: LiveValuesToBeDeleted) {
- Info.LiveSet.erase(LiveValue);
- }
- }
- static bool insertParsePoints(Function &F, DominatorTree &DT,
- TargetTransformInfo &TTI,
- SmallVectorImpl<CallSite> &ToUpdate) {
- #ifndef NDEBUG
- // sanity check the input
- std::set<CallSite> Uniqued;
- Uniqued.insert(ToUpdate.begin(), ToUpdate.end());
- assert(Uniqued.size() == ToUpdate.size() && "no duplicates please!");
- for (CallSite CS : ToUpdate) {
- assert(CS.getInstruction()->getParent()->getParent() == &F);
- assert((UseDeoptBundles || isStatepoint(CS)) &&
- "expected to already be a deopt statepoint");
- }
- #endif
- // When inserting gc.relocates for invokes, we need to be able to insert at
- // the top of the successor blocks. See the comment on
- // normalForInvokeSafepoint on exactly what is needed. Note that this step
- // may restructure the CFG.
- for (CallSite CS : ToUpdate) {
- if (!CS.isInvoke())
- continue;
- auto *II = cast<InvokeInst>(CS.getInstruction());
- normalizeForInvokeSafepoint(II->getNormalDest(), II->getParent(), DT);
- normalizeForInvokeSafepoint(II->getUnwindDest(), II->getParent(), DT);
- }
- // A list of dummy calls added to the IR to keep various values obviously
- // live in the IR. We'll remove all of these when done.
- SmallVector<CallInst *, 64> Holders;
- // Insert a dummy call with all of the arguments to the vm_state we'll need
- // for the actual safepoint insertion. This ensures reference arguments in
- // the deopt argument list are considered live through the safepoint (and
- // thus makes sure they get relocated.)
- for (CallSite CS : ToUpdate) {
- SmallVector<Value *, 64> DeoptValues;
- iterator_range<const Use *> DeoptStateRange =
- UseDeoptBundles
- ? iterator_range<const Use *>(GetDeoptBundleOperands(CS))
- : iterator_range<const Use *>(Statepoint(CS).vm_state_args());
- for (Value *Arg : DeoptStateRange) {
- assert(!isUnhandledGCPointerType(Arg->getType()) &&
- "support for FCA unimplemented");
- if (isHandledGCPointerType(Arg->getType()))
- DeoptValues.push_back(Arg);
- }
- insertUseHolderAfter(CS, DeoptValues, Holders);
- }
- SmallVector<PartiallyConstructedSafepointRecord, 64> Records(ToUpdate.size());
- // A) Identify all gc pointers which are statically live at the given call
- // site.
- findLiveReferences(F, DT, ToUpdate, Records);
- // B) Find the base pointers for each live pointer
- /* scope for caching */ {
- // Cache the 'defining value' relation used in the computation and
- // insertion of base phis and selects. This ensures that we don't insert
- // large numbers of duplicate base_phis.
- DefiningValueMapTy DVCache;
- for (size_t i = 0; i < Records.size(); i++) {
- PartiallyConstructedSafepointRecord &info = Records[i];
- findBasePointers(DT, DVCache, ToUpdate[i], info);
- }
- } // end of cache scope
- // The base phi insertion logic (for any safepoint) may have inserted new
- // instructions which are now live at some safepoint. The simplest such
- // example is:
- // loop:
- // phi a <-- will be a new base_phi here
- // safepoint 1 <-- that needs to be live here
- // gep a + 1
- // safepoint 2
- // br loop
- // We insert some dummy calls after each safepoint to definitely hold live
- // the base pointers which were identified for that safepoint. We'll then
- // ask liveness for _every_ base inserted to see what is now live. Then we
- // remove the dummy calls.
- Holders.reserve(Holders.size() + Records.size());
- for (size_t i = 0; i < Records.size(); i++) {
- PartiallyConstructedSafepointRecord &Info = Records[i];
- SmallVector<Value *, 128> Bases;
- for (auto Pair : Info.PointerToBase)
- Bases.push_back(Pair.second);
- insertUseHolderAfter(ToUpdate[i], Bases, Holders);
- }
- // By selecting base pointers, we've effectively inserted new uses. Thus, we
- // need to rerun liveness. We may *also* have inserted new defs, but that's
- // not the key issue.
- recomputeLiveInValues(F, DT, ToUpdate, Records);
- if (PrintBasePointers) {
- for (auto &Info : Records) {
- errs() << "Base Pairs: (w/Relocation)\n";
- for (auto Pair : Info.PointerToBase) {
- errs() << " derived ";
- Pair.first->printAsOperand(errs(), false);
- errs() << " base ";
- Pair.second->printAsOperand(errs(), false);
- errs() << "\n";
- }
- }
- }
- // It is possible that non-constant live variables have a constant base. For
- // example, a GEP with a variable offset from a global. In this case we can
- // remove it from the liveset. We already don't add constants to the liveset
- // because we assume they won't move at runtime and the GC doesn't need to be
- // informed about them. The same reasoning applies if the base is constant.
- // Note that the relocation placement code relies on this filtering for
- // correctness as it expects the base to be in the liveset, which isn't true
- // if the base is constant.
- for (auto &Info : Records)
- for (auto &BasePair : Info.PointerToBase)
- if (isa<Constant>(BasePair.second))
- Info.LiveSet.erase(BasePair.first);
- for (CallInst *CI : Holders)
- CI->eraseFromParent();
- Holders.clear();
- // Do a limited scalarization of any live at safepoint vector values which
- // contain pointers. This enables this pass to run after vectorization at
- // the cost of some possible performance loss. Note: This is known to not
- // handle updating of the side tables correctly which can lead to relocation
- // bugs when the same vector is live at multiple statepoints. We're in the
- // process of implementing the alternate lowering - relocating the
- // vector-of-pointers as first class item and updating the backend to
- // understand that - but that's not yet complete.
- if (UseVectorSplit)
- for (size_t i = 0; i < Records.size(); i++) {
- PartiallyConstructedSafepointRecord &Info = Records[i];
- Instruction *Statepoint = ToUpdate[i].getInstruction();
- splitVectorValues(cast<Instruction>(Statepoint), Info.LiveSet,
- Info.PointerToBase, DT);
- }
- // In order to reduce live set of statepoint we might choose to rematerialize
- // some values instead of relocating them. This is purely an optimization and
- // does not influence correctness.
- for (size_t i = 0; i < Records.size(); i++)
- rematerializeLiveValues(ToUpdate[i], Records[i], TTI);
- // We need this to safely RAUW and delete call or invoke return values that
- // may themselves be live over a statepoint. For details, please see usage in
- // makeStatepointExplicitImpl.
- std::vector<DeferredReplacement> Replacements;
- // Now run through and replace the existing statepoints with new ones with
- // the live variables listed. We do not yet update uses of the values being
- // relocated. We have references to live variables that need to
- // survive to the last iteration of this loop. (By construction, the
- // previous statepoint can not be a live variable, thus we can and remove
- // the old statepoint calls as we go.)
- for (size_t i = 0; i < Records.size(); i++)
- makeStatepointExplicit(DT, ToUpdate[i], Records[i], Replacements);
- ToUpdate.clear(); // prevent accident use of invalid CallSites
- for (auto &PR : Replacements)
- PR.doReplacement();
- Replacements.clear();
- for (auto &Info : Records) {
- // These live sets may contain state Value pointers, since we replaced calls
- // with operand bundles with calls wrapped in gc.statepoint, and some of
- // those calls may have been def'ing live gc pointers. Clear these out to
- // avoid accidentally using them.
- //
- // TODO: We should create a separate data structure that does not contain
- // these live sets, and migrate to using that data structure from this point
- // onward.
- Info.LiveSet.clear();
- Info.PointerToBase.clear();
- }
- // Do all the fixups of the original live variables to their relocated selves
- SmallVector<Value *, 128> Live;
- for (size_t i = 0; i < Records.size(); i++) {
- PartiallyConstructedSafepointRecord &Info = Records[i];
- // We can't simply save the live set from the original insertion. One of
- // the live values might be the result of a call which needs a safepoint.
- // That Value* no longer exists and we need to use the new gc_result.
- // Thankfully, the live set is embedded in the statepoint (and updated), so
- // we just grab that.
- Statepoint Statepoint(Info.StatepointToken);
- Live.insert(Live.end(), Statepoint.gc_args_begin(),
- Statepoint.gc_args_end());
- #ifndef NDEBUG
- // Do some basic sanity checks on our liveness results before performing
- // relocation. Relocation can and will turn mistakes in liveness results
- // into non-sensical code which is must harder to debug.
- // TODO: It would be nice to test consistency as well
- assert(DT.isReachableFromEntry(Info.StatepointToken->getParent()) &&
- "statepoint must be reachable or liveness is meaningless");
- for (Value *V : Statepoint.gc_args()) {
- if (!isa<Instruction>(V))
- // Non-instruction values trivial dominate all possible uses
- continue;
- auto *LiveInst = cast<Instruction>(V);
- assert(DT.isReachableFromEntry(LiveInst->getParent()) &&
- "unreachable values should never be live");
- assert(DT.dominates(LiveInst, Info.StatepointToken) &&
- "basic SSA liveness expectation violated by liveness analysis");
- }
- #endif
- }
- unique_unsorted(Live);
- #ifndef NDEBUG
- // sanity check
- for (auto *Ptr : Live)
- assert(isHandledGCPointerType(Ptr->getType()) &&
- "must be a gc pointer type");
- #endif
- relocationViaAlloca(F, DT, Live, Records);
- return !Records.empty();
- }
- // Handles both return values and arguments for Functions and CallSites.
- template <typename AttrHolder>
- static void RemoveNonValidAttrAtIndex(LLVMContext &Ctx, AttrHolder &AH,
- unsigned Index) {
- AttrBuilder R;
- if (AH.getDereferenceableBytes(Index))
- R.addAttribute(Attribute::get(Ctx, Attribute::Dereferenceable,
- AH.getDereferenceableBytes(Index)));
- if (AH.getDereferenceableOrNullBytes(Index))
- R.addAttribute(Attribute::get(Ctx, Attribute::DereferenceableOrNull,
- AH.getDereferenceableOrNullBytes(Index)));
- if (AH.doesNotAlias(Index))
- R.addAttribute(Attribute::NoAlias);
- if (!R.empty())
- AH.setAttributes(AH.getAttributes().removeAttributes(
- Ctx, Index, AttributeSet::get(Ctx, Index, R)));
- }
- void
- RewriteStatepointsForGC::stripNonValidAttributesFromPrototype(Function &F) {
- LLVMContext &Ctx = F.getContext();
- for (Argument &A : F.args())
- if (isa<PointerType>(A.getType()))
- RemoveNonValidAttrAtIndex(Ctx, F, A.getArgNo() + 1);
- if (isa<PointerType>(F.getReturnType()))
- RemoveNonValidAttrAtIndex(Ctx, F, AttributeSet::ReturnIndex);
- }
- void RewriteStatepointsForGC::stripNonValidAttributesFromBody(Function &F) {
- if (F.empty())
- return;
- LLVMContext &Ctx = F.getContext();
- MDBuilder Builder(Ctx);
- for (Instruction &I : instructions(F)) {
- if (const MDNode *MD = I.getMetadata(LLVMContext::MD_tbaa)) {
- assert(MD->getNumOperands() < 5 && "unrecognized metadata shape!");
- bool IsImmutableTBAA =
- MD->getNumOperands() == 4 &&
- mdconst::extract<ConstantInt>(MD->getOperand(3))->getValue() == 1;
- if (!IsImmutableTBAA)
- continue; // no work to do, MD_tbaa is already marked mutable
- MDNode *Base = cast<MDNode>(MD->getOperand(0));
- MDNode *Access = cast<MDNode>(MD->getOperand(1));
- uint64_t Offset =
- mdconst::extract<ConstantInt>(MD->getOperand(2))->getZExtValue();
- MDNode *MutableTBAA =
- Builder.createTBAAStructTagNode(Base, Access, Offset);
- I.setMetadata(LLVMContext::MD_tbaa, MutableTBAA);
- }
- if (CallSite CS = CallSite(&I)) {
- for (int i = 0, e = CS.arg_size(); i != e; i++)
- if (isa<PointerType>(CS.getArgument(i)->getType()))
- RemoveNonValidAttrAtIndex(Ctx, CS, i + 1);
- if (isa<PointerType>(CS.getType()))
- RemoveNonValidAttrAtIndex(Ctx, CS, AttributeSet::ReturnIndex);
- }
- }
- }
- /// Returns true if this function should be rewritten by this pass. The main
- /// point of this function is as an extension point for custom logic.
- static bool shouldRewriteStatepointsIn(Function &F) {
- // TODO: This should check the GCStrategy
- if (F.hasGC()) {
- const auto &FunctionGCName = F.getGC();
- const StringRef StatepointExampleName("statepoint-example");
- const StringRef CoreCLRName("coreclr");
- return (StatepointExampleName == FunctionGCName) ||
- (CoreCLRName == FunctionGCName);
- } else
- return false;
- }
- void RewriteStatepointsForGC::stripNonValidAttributes(Module &M) {
- #ifndef NDEBUG
- assert(std::any_of(M.begin(), M.end(), shouldRewriteStatepointsIn) &&
- "precondition!");
- #endif
- for (Function &F : M)
- stripNonValidAttributesFromPrototype(F);
- for (Function &F : M)
- stripNonValidAttributesFromBody(F);
- }
- bool RewriteStatepointsForGC::runOnFunction(Function &F) {
- // Nothing to do for declarations.
- if (F.isDeclaration() || F.empty())
- return false;
- // Policy choice says not to rewrite - the most common reason is that we're
- // compiling code without a GCStrategy.
- if (!shouldRewriteStatepointsIn(F))
- return false;
- DominatorTree &DT = getAnalysis<DominatorTreeWrapperPass>(F).getDomTree();
- TargetTransformInfo &TTI =
- getAnalysis<TargetTransformInfoWrapperPass>().getTTI(F);
- auto NeedsRewrite = [](Instruction &I) {
- if (UseDeoptBundles) {
- if (ImmutableCallSite CS = ImmutableCallSite(&I))
- return !callsGCLeafFunction(CS);
- return false;
- }
- return isStatepoint(I);
- };
- // Gather all the statepoints which need rewritten. Be careful to only
- // consider those in reachable code since we need to ask dominance queries
- // when rewriting. We'll delete the unreachable ones in a moment.
- SmallVector<CallSite, 64> ParsePointNeeded;
- bool HasUnreachableStatepoint = false;
- for (Instruction &I : instructions(F)) {
- // TODO: only the ones with the flag set!
- if (NeedsRewrite(I)) {
- if (DT.isReachableFromEntry(I.getParent()))
- ParsePointNeeded.push_back(CallSite(&I));
- else
- HasUnreachableStatepoint = true;
- }
- }
- bool MadeChange = false;
- // Delete any unreachable statepoints so that we don't have unrewritten
- // statepoints surviving this pass. This makes testing easier and the
- // resulting IR less confusing to human readers. Rather than be fancy, we
- // just reuse a utility function which removes the unreachable blocks.
- if (HasUnreachableStatepoint)
- MadeChange |= removeUnreachableBlocks(F);
- // Return early if no work to do.
- if (ParsePointNeeded.empty())
- return MadeChange;
- // As a prepass, go ahead and aggressively destroy single entry phi nodes.
- // These are created by LCSSA. They have the effect of increasing the size
- // of liveness sets for no good reason. It may be harder to do this post
- // insertion since relocations and base phis can confuse things.
- for (BasicBlock &BB : F)
- if (BB.getUniquePredecessor()) {
- MadeChange = true;
- FoldSingleEntryPHINodes(&BB);
- }
- // Before we start introducing relocations, we want to tweak the IR a bit to
- // avoid unfortunate code generation effects. The main example is that we
- // want to try to make sure the comparison feeding a branch is after any
- // safepoints. Otherwise, we end up with a comparison of pre-relocation
- // values feeding a branch after relocation. This is semantically correct,
- // but results in extra register pressure since both the pre-relocation and
- // post-relocation copies must be available in registers. For code without
- // relocations this is handled elsewhere, but teaching the scheduler to
- // reverse the transform we're about to do would be slightly complex.
- // Note: This may extend the live range of the inputs to the icmp and thus
- // increase the liveset of any statepoint we move over. This is profitable
- // as long as all statepoints are in rare blocks. If we had in-register
- // lowering for live values this would be a much safer transform.
- auto getConditionInst = [](TerminatorInst *TI) -> Instruction* {
- if (auto *BI = dyn_cast<BranchInst>(TI))
- if (BI->isConditional())
- return dyn_cast<Instruction>(BI->getCondition());
- // TODO: Extend this to handle switches
- return nullptr;
- };
- for (BasicBlock &BB : F) {
- TerminatorInst *TI = BB.getTerminator();
- if (auto *Cond = getConditionInst(TI))
- // TODO: Handle more than just ICmps here. We should be able to move
- // most instructions without side effects or memory access.
- if (isa<ICmpInst>(Cond) && Cond->hasOneUse()) {
- MadeChange = true;
- Cond->moveBefore(TI);
- }
- }
- MadeChange |= insertParsePoints(F, DT, TTI, ParsePointNeeded);
- return MadeChange;
- }
- // liveness computation via standard dataflow
- // -------------------------------------------------------------------
- // TODO: Consider using bitvectors for liveness, the set of potentially
- // interesting values should be small and easy to pre-compute.
- /// Compute the live-in set for the location rbegin starting from
- /// the live-out set of the basic block
- static void computeLiveInValues(BasicBlock::reverse_iterator rbegin,
- BasicBlock::reverse_iterator rend,
- DenseSet<Value *> &LiveTmp) {
- for (BasicBlock::reverse_iterator ritr = rbegin; ritr != rend; ritr++) {
- Instruction *I = &*ritr;
- // KILL/Def - Remove this definition from LiveIn
- LiveTmp.erase(I);
- // Don't consider *uses* in PHI nodes, we handle their contribution to
- // predecessor blocks when we seed the LiveOut sets
- if (isa<PHINode>(I))
- continue;
- // USE - Add to the LiveIn set for this instruction
- for (Value *V : I->operands()) {
- assert(!isUnhandledGCPointerType(V->getType()) &&
- "support for FCA unimplemented");
- if (isHandledGCPointerType(V->getType()) && !isa<Constant>(V)) {
- // The choice to exclude all things constant here is slightly subtle.
- // There are two independent reasons:
- // - We assume that things which are constant (from LLVM's definition)
- // do not move at runtime. For example, the address of a global
- // variable is fixed, even though it's contents may not be.
- // - Second, we can't disallow arbitrary inttoptr constants even
- // if the language frontend does. Optimization passes are free to
- // locally exploit facts without respect to global reachability. This
- // can create sections of code which are dynamically unreachable and
- // contain just about anything. (see constants.ll in tests)
- LiveTmp.insert(V);
- }
- }
- }
- }
- static void computeLiveOutSeed(BasicBlock *BB, DenseSet<Value *> &LiveTmp) {
- for (BasicBlock *Succ : successors(BB)) {
- const BasicBlock::iterator E(Succ->getFirstNonPHI());
- for (BasicBlock::iterator I = Succ->begin(); I != E; I++) {
- PHINode *Phi = cast<PHINode>(&*I);
- Value *V = Phi->getIncomingValueForBlock(BB);
- assert(!isUnhandledGCPointerType(V->getType()) &&
- "support for FCA unimplemented");
- if (isHandledGCPointerType(V->getType()) && !isa<Constant>(V)) {
- LiveTmp.insert(V);
- }
- }
- }
- }
- static DenseSet<Value *> computeKillSet(BasicBlock *BB) {
- DenseSet<Value *> KillSet;
- for (Instruction &I : *BB)
- if (isHandledGCPointerType(I.getType()))
- KillSet.insert(&I);
- return KillSet;
- }
- #ifndef NDEBUG
- /// Check that the items in 'Live' dominate 'TI'. This is used as a basic
- /// sanity check for the liveness computation.
- static void checkBasicSSA(DominatorTree &DT, DenseSet<Value *> &Live,
- TerminatorInst *TI, bool TermOkay = false) {
- for (Value *V : Live) {
- if (auto *I = dyn_cast<Instruction>(V)) {
- // The terminator can be a member of the LiveOut set. LLVM's definition
- // of instruction dominance states that V does not dominate itself. As
- // such, we need to special case this to allow it.
- if (TermOkay && TI == I)
- continue;
- assert(DT.dominates(I, TI) &&
- "basic SSA liveness expectation violated by liveness analysis");
- }
- }
- }
- /// Check that all the liveness sets used during the computation of liveness
- /// obey basic SSA properties. This is useful for finding cases where we miss
- /// a def.
- static void checkBasicSSA(DominatorTree &DT, GCPtrLivenessData &Data,
- BasicBlock &BB) {
- checkBasicSSA(DT, Data.LiveSet[&BB], BB.getTerminator());
- checkBasicSSA(DT, Data.LiveOut[&BB], BB.getTerminator(), true);
- checkBasicSSA(DT, Data.LiveIn[&BB], BB.getTerminator());
- }
- #endif
- static void computeLiveInValues(DominatorTree &DT, Function &F,
- GCPtrLivenessData &Data) {
- SmallSetVector<BasicBlock *, 200> Worklist;
- auto AddPredsToWorklist = [&](BasicBlock *BB) {
- // We use a SetVector so that we don't have duplicates in the worklist.
- Worklist.insert(pred_begin(BB), pred_end(BB));
- };
- auto NextItem = [&]() {
- BasicBlock *BB = Worklist.back();
- Worklist.pop_back();
- return BB;
- };
- // Seed the liveness for each individual block
- for (BasicBlock &BB : F) {
- Data.KillSet[&BB] = computeKillSet(&BB);
- Data.LiveSet[&BB].clear();
- computeLiveInValues(BB.rbegin(), BB.rend(), Data.LiveSet[&BB]);
- #ifndef NDEBUG
- for (Value *Kill : Data.KillSet[&BB])
- assert(!Data.LiveSet[&BB].count(Kill) && "live set contains kill");
- #endif
- Data.LiveOut[&BB] = DenseSet<Value *>();
- computeLiveOutSeed(&BB, Data.LiveOut[&BB]);
- Data.LiveIn[&BB] = Data.LiveSet[&BB];
- set_union(Data.LiveIn[&BB], Data.LiveOut[&BB]);
- set_subtract(Data.LiveIn[&BB], Data.KillSet[&BB]);
- if (!Data.LiveIn[&BB].empty())
- AddPredsToWorklist(&BB);
- }
- // Propagate that liveness until stable
- while (!Worklist.empty()) {
- BasicBlock *BB = NextItem();
- // Compute our new liveout set, then exit early if it hasn't changed
- // despite the contribution of our successor.
- DenseSet<Value *> LiveOut = Data.LiveOut[BB];
- const auto OldLiveOutSize = LiveOut.size();
- for (BasicBlock *Succ : successors(BB)) {
- assert(Data.LiveIn.count(Succ));
- set_union(LiveOut, Data.LiveIn[Succ]);
- }
- // assert OutLiveOut is a subset of LiveOut
- if (OldLiveOutSize == LiveOut.size()) {
- // If the sets are the same size, then we didn't actually add anything
- // when unioning our successors LiveIn Thus, the LiveIn of this block
- // hasn't changed.
- continue;
- }
- Data.LiveOut[BB] = LiveOut;
- // Apply the effects of this basic block
- DenseSet<Value *> LiveTmp = LiveOut;
- set_union(LiveTmp, Data.LiveSet[BB]);
- set_subtract(LiveTmp, Data.KillSet[BB]);
- assert(Data.LiveIn.count(BB));
- const DenseSet<Value *> &OldLiveIn = Data.LiveIn[BB];
- // assert: OldLiveIn is a subset of LiveTmp
- if (OldLiveIn.size() != LiveTmp.size()) {
- Data.LiveIn[BB] = LiveTmp;
- AddPredsToWorklist(BB);
- }
- } // while( !worklist.empty() )
- #ifndef NDEBUG
- // Sanity check our output against SSA properties. This helps catch any
- // missing kills during the above iteration.
- for (BasicBlock &BB : F) {
- checkBasicSSA(DT, Data, BB);
- }
- #endif
- }
- static void findLiveSetAtInst(Instruction *Inst, GCPtrLivenessData &Data,
- StatepointLiveSetTy &Out) {
- BasicBlock *BB = Inst->getParent();
- // Note: The copy is intentional and required
- assert(Data.LiveOut.count(BB));
- DenseSet<Value *> LiveOut = Data.LiveOut[BB];
- // We want to handle the statepoint itself oddly. It's
- // call result is not live (normal), nor are it's arguments
- // (unless they're used again later). This adjustment is
- // specifically what we need to relocate
- BasicBlock::reverse_iterator rend(Inst->getIterator());
- computeLiveInValues(BB->rbegin(), rend, LiveOut);
- LiveOut.erase(Inst);
- Out.insert(LiveOut.begin(), LiveOut.end());
- }
- static void recomputeLiveInValues(GCPtrLivenessData &RevisedLivenessData,
- const CallSite &CS,
- PartiallyConstructedSafepointRecord &Info) {
- Instruction *Inst = CS.getInstruction();
- StatepointLiveSetTy Updated;
- findLiveSetAtInst(Inst, RevisedLivenessData, Updated);
- #ifndef NDEBUG
- DenseSet<Value *> Bases;
- for (auto KVPair : Info.PointerToBase) {
- Bases.insert(KVPair.second);
- }
- #endif
- // We may have base pointers which are now live that weren't before. We need
- // to update the PointerToBase structure to reflect this.
- for (auto V : Updated)
- if (!Info.PointerToBase.count(V)) {
- assert(Bases.count(V) && "can't find base for unexpected live value");
- Info.PointerToBase[V] = V;
- continue;
- }
- #ifndef NDEBUG
- for (auto V : Updated) {
- assert(Info.PointerToBase.count(V) &&
- "must be able to find base for live value");
- }
- #endif
- // Remove any stale base mappings - this can happen since our liveness is
- // more precise then the one inherent in the base pointer analysis
- DenseSet<Value *> ToErase;
- for (auto KVPair : Info.PointerToBase)
- if (!Updated.count(KVPair.first))
- ToErase.insert(KVPair.first);
- for (auto V : ToErase)
- Info.PointerToBase.erase(V);
- #ifndef NDEBUG
- for (auto KVPair : Info.PointerToBase)
- assert(Updated.count(KVPair.first) && "record for non-live value");
- #endif
- Info.LiveSet = Updated;
- }
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