ADT/STLExtras: Introduce llvm::empty; NFC

This is modeled after C++17 std::empty().

Differential Revision: https://reviews.llvm.org/D53909

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@345679 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/ADT/STLExtras.h

@@ -195,6 +195,12 @@ void adl_swap(T &&lhs, T &&rhs) noexcept(
   adl_detail::adl_swap(std::forward<T>(lhs), std::forward<T>(rhs));
 }
 
+/// Test whether \p RangeOrContainer is empty. Similar to C++17 std::empty.
+template <typename T>
+constexpr bool empty(const T &RangeOrContainer) {
+  return adl_begin(RangeOrContainer) == adl_end(RangeOrContainer);
+}
+
 // mapped_iterator - This is a simple iterator adapter that causes a function to
 // be applied whenever operator* is invoked on the iterator.
 

lib/Analysis/LazyCallGraph.cpp

@@ -619,7 +619,7 @@ LazyCallGraph::RefSCC::switchInternalEdgeToCall(
 
   // If the merge range is empty, then adding the edge didn't actually form any
   // new cycles. We're done.
-  if (MergeRange.begin() == MergeRange.end()) {
+  if (empty(MergeRange)) {
     // Now that the SCC structure is finalized, flip the kind to call.
     SourceN->setEdgeKind(TargetN, Edge::Call);
     return false; // No new cycle.

lib/CodeGen/GlobalISel/InstructionSelector.cpp

@@ -80,5 +80,5 @@ bool InstructionSelector::isObviouslySafeToFold(MachineInstr &MI,
     return true;
 
   return !MI.mayLoadOrStore() && !MI.hasUnmodeledSideEffects() &&
-         MI.implicit_operands().begin() == MI.implicit_operands().end();
+         empty(MI.implicit_operands());
 }

lib/CodeGen/GlobalISel/LegalizerInfo.cpp

@@ -298,8 +298,7 @@ LegalizeRuleSet &LegalizerInfo::getActionDefinitionsBuilder(
     std::initializer_list<unsigned> Opcodes) {
   unsigned Representative = *Opcodes.begin();
 
-  assert(Opcodes.begin() != Opcodes.end() &&
-         Opcodes.begin() + 1 != Opcodes.end() &&
+  assert(!empty(Opcodes) && Opcodes.begin() + 1 != Opcodes.end() &&
          "Initializer list must have at least two opcodes");
 
   for (auto I = Opcodes.begin() + 1, E = Opcodes.end(); I != E; ++I)

lib/CodeGen/GlobalISel/RegBankSelect.cpp

@@ -140,7 +140,7 @@ bool RegBankSelect::repairReg(
     return false;
   assert(ValMapping.NumBreakDowns == 1 && "Not yet implemented");
   // An empty range of new register means no repairing.
-  assert(NewVRegs.begin() != NewVRegs.end() && "We should not have to repair");
+  assert(!empty(NewVRegs) && "We should not have to repair");
 
   // Assume we are repairing a use and thus, the original reg will be
   // the source of the repairing.

lib/CodeGen/GlobalISel/RegisterBankInfo.cpp

@@ -426,7 +426,7 @@ void RegisterBankInfo::applyDefaultMapping(const OperandsMapper &OpdMapper) {
            "This mapping is too complex for this function");
     iterator_range<SmallVectorImpl<unsigned>::const_iterator> NewRegs =
         OpdMapper.getVRegs(OpIdx);
-    if (NewRegs.begin() == NewRegs.end()) {
+    if (empty(NewRegs)) {
       LLVM_DEBUG(dbgs() << " has not been repaired, nothing to be done\n");
       continue;
     }

lib/ExecutionEngine/Orc/ExecutionUtils.cpp

@@ -88,7 +88,7 @@ iterator_range<CtorDtorIterator> getDestructors(const Module &M) {
 }
 
 void CtorDtorRunner::add(iterator_range<CtorDtorIterator> CtorDtors) {
-  if (CtorDtors.begin() == CtorDtors.end())
+  if (empty(CtorDtors))
     return;
 
   MangleAndInterner Mangle(

lib/IR/DebugInfo.cpp

@@ -280,7 +280,7 @@ bool DebugInfoFinder::addScope(DIScope *Scope) {
 }
 
 static MDNode *stripDebugLocFromLoopID(MDNode *N) {
-  assert(N->op_begin() != N->op_end() && "Missing self reference?");
+  assert(!empty(N->operands()) && "Missing self reference?");
 
   // if there is no debug location, we do not have to rewrite this MDNode.
   if (std::none_of(N->op_begin() + 1, N->op_end(), [](const MDOperand &Op) {

lib/Transforms/IPO/PartialInlining.cpp

@@ -1251,7 +1251,7 @@ std::pair<bool, Function *> PartialInlinerImpl::unswitchFunction(Function *F) {
   if (PSI->isFunctionEntryCold(F))
     return {false, nullptr};
 
-  if (F->user_begin() == F->user_end())
+  if (empty(F->users()))
     return {false, nullptr};
 
   OptimizationRemarkEmitter ORE(F);
@@ -1357,7 +1357,7 @@ bool PartialInlinerImpl::tryPartialInline(FunctionCloner &Cloner) {
     return false;
   }
 
-  assert(Cloner.OrigFunc->user_begin() == Cloner.OrigFunc->user_end() &&
+  assert(empty(Cloner.OrigFunc->users()) &&
          "F's users should all be replaced!");
 
   std::vector<User *> Users(Cloner.ClonedFunc->user_begin(),

lib/Transforms/Scalar/NewGVN.cpp

@@ -1751,7 +1751,7 @@ NewGVN::performSymbolicPHIEvaluation(ArrayRef<ValPair> PHIOps,
     return true;
   });
   // If we are left with no operands, it's dead.
-  if (Filtered.begin() == Filtered.end()) {
+  if (empty(Filtered)) {
     // If it has undef at this point, it means there are no-non-undef arguments,
     // and thus, the value of the phi node must be undef.
     if (HasUndef) {

lib/Transforms/Utils/PredicateInfo.cpp

@@ -522,7 +522,7 @@ Value *PredicateInfo::materializeStack(unsigned int &Counter,
     if (isa<PredicateWithEdge>(ValInfo)) {
       IRBuilder<> B(getBranchTerminator(ValInfo));
       Function *IF = getCopyDeclaration(F.getParent(), Op->getType());
-      if (IF->user_begin() == IF->user_end())
+      if (empty(IF->users()))
         CreatedDeclarations.insert(IF);
       CallInst *PIC =
           B.CreateCall(IF, Op, Op->getName() + "." + Twine(Counter++));
@@ -534,7 +534,7 @@ Value *PredicateInfo::materializeStack(unsigned int &Counter,
              "Should not have gotten here without it being an assume");
       IRBuilder<> B(PAssume->AssumeInst);
       Function *IF = getCopyDeclaration(F.getParent(), Op->getType());
-      if (IF->user_begin() == IF->user_end())
+      if (empty(IF->users()))
         CreatedDeclarations.insert(IF);
       CallInst *PIC = B.CreateCall(IF, Op);
       PredicateMap.insert({PIC, ValInfo});

lib/Transforms/Utils/SimplifyCFG.cpp

@@ -5260,7 +5260,7 @@ static bool SwitchToLookupTable(SwitchInst *SI, IRBuilder<> &Builder,
 
   // Figure out the corresponding result for each case value and phi node in the
   // common destination, as well as the min and max case values.
-  assert(SI->case_begin() != SI->case_end());
+  assert(!empty(SI->cases()));
   SwitchInst::CaseIt CI = SI->case_begin();
   ConstantInt *MinCaseVal = CI->getCaseValue();
   ConstantInt *MaxCaseVal = CI->getCaseValue();

unittests/ADT/STLExtrasTest.cpp

@@ -364,6 +364,23 @@ TEST(STLExtrasTest, ADLTest) {
   EXPECT_EQ(5, count);
 }
 
+TEST(STLExtrasTest, EmptyTest) {
+  std::vector<void*> V;
+  EXPECT_TRUE(empty(V));
+  V.push_back(nullptr);
+  EXPECT_FALSE(empty(V));
+
+  std::initializer_list<int> E = {};
+  std::initializer_list<int> NotE = {7, 13, 42};
+  EXPECT_TRUE(empty(E));
+  EXPECT_FALSE(empty(NotE));
+
+  auto R0 = make_range(V.begin(), V.begin());
+  EXPECT_TRUE(empty(R0));
+  auto R1 = make_range(V.begin(), V.end());
+  EXPECT_FALSE(empty(R1));
+}
+
 TEST(STLExtrasTest, EarlyIncrementTest) {
   std::list<int> L = {1, 2, 3, 4};