Reland "[WebAssembly] LSDA info generation"

Summary:
This adds support for LSDA (exception table) generation for wasm EH.
Wasm EH mostly follows the structure of Itanium-style exception tables,
with one exception: a call site table entry in wasm EH corresponds to
not a call site but a landing pad.

In wasm EH, the VM is responsible for stack unwinding. After an
exception occurs and the stack is unwound, the control flow is
transferred to wasm 'catch' instruction by the VM, after which the
personality function is called from the compiler-generated code. (Refer
to WasmEHPrepare pass for more information on this part.)

This patch:
- Changes wasm.landingpad.index intrinsic to take a token argument, to
make this 1:1 match with a catchpad instruction
- Stores landingpad index info and catch type info MachineFunction in
before instruction selection
- Lowers wasm.lsda intrinsic to an MCSymbol pointing to the start of an
exception table
- Adds WasmException class with overridden methods for table generation
- Adds support for LSDA section in Wasm object writer

Reviewers: dschuff, sbc100, rnk

Subscribers: mgorny, jgravelle-google, sunfish, llvm-commits

Differential Revision: https://reviews.llvm.org/D52748

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@345345 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/CodeGen/MachineFunction.h

@@ -316,6 +316,9 @@ class MachineFunction {
   /// Map a landing pad's EH symbol to the call site indexes.
   DenseMap<MCSymbol*, SmallVector<unsigned, 4>> LPadToCallSiteMap;
 
+  /// Map a landing pad to its index.
+  DenseMap<const MachineBasicBlock *, unsigned> WasmLPadToIndexMap;
+
   /// Map of invoke call site index values to associated begin EH_LABEL.
   DenseMap<MCSymbol*, unsigned> CallSiteMap;
 
@@ -810,7 +813,8 @@ public:
   LandingPadInfo &getOrCreateLandingPadInfo(MachineBasicBlock *LandingPad);
 
   /// Remap landing pad labels and remove any deleted landing pads.
-  void tidyLandingPads(DenseMap<MCSymbol*, uintptr_t> *LPMap = nullptr);
+  void tidyLandingPads(DenseMap<MCSymbol *, uintptr_t> *LPMap = nullptr,
+                       bool TidyIfNoBeginLabels = true);
 
   /// Return a reference to the landing pad info for the current function.
   const std::vector<LandingPadInfo> &getLandingPads() const {
@@ -853,6 +857,22 @@ public:
   /// Map the landing pad's EH symbol to the call site indexes.
   void setCallSiteLandingPad(MCSymbol *Sym, ArrayRef<unsigned> Sites);
 
+  /// Map the landing pad to its index. Used for Wasm exception handling.
+  void setWasmLandingPadIndex(const MachineBasicBlock *LPad, unsigned Index) {
+    WasmLPadToIndexMap[LPad] = Index;
+  }
+
+  /// Returns true if the landing pad has an associate index in wasm EH.
+  bool hasWasmLandingPadIndex(const MachineBasicBlock *LPad) const {
+    return WasmLPadToIndexMap.count(LPad);
+  }
+
+  /// Get the index in wasm EH for a given landing pad.
+  unsigned getWasmLandingPadIndex(const MachineBasicBlock *LPad) const {
+    assert(hasWasmLandingPadIndex(LPad));
+    return WasmLPadToIndexMap.lookup(LPad);
+  }
+
   /// Get the call site indexes for a landing pad EH symbol.
   SmallVectorImpl<unsigned> &getCallSiteLandingPad(MCSymbol *Sym) {
     assert(hasCallSiteLandingPad(Sym) &&

include/llvm/IR/IntrinsicsWebAssembly.td

@@ -71,7 +71,8 @@ def int_wasm_catch : Intrinsic<[llvm_ptr_ty], [llvm_i32_ty],
 // WebAssembly EH must maintain the landingpads in the order assigned to them
 // by WasmEHPrepare pass to generate landingpad table in EHStreamer. This is
 // used in order to give them the indices in WasmEHPrepare.
-def int_wasm_landingpad_index: Intrinsic<[], [llvm_i32_ty], [IntrNoMem]>;
+def int_wasm_landingpad_index: Intrinsic<[], [llvm_token_ty, llvm_i32_ty],
+                                         [IntrNoMem]>;
 
 // Returns LSDA address of the current function.
 def int_wasm_lsda : Intrinsic<[llvm_ptr_ty], [], [IntrNoMem]>;

lib/CodeGen/AsmPrinter/AsmPrinter.cpp

@@ -16,6 +16,7 @@
 #include "CodeViewDebug.h"
 #include "DwarfDebug.h"
 #include "DwarfException.h"
+#include "WasmException.h"
 #include "WinCFGuard.h"
 #include "WinException.h"
 #include "llvm/ADT/APFloat.h"
@@ -356,7 +357,7 @@ bool AsmPrinter::doInitialization(Module &M) {
     }
     break;
   case ExceptionHandling::Wasm:
-    // TODO to prevent warning
+    ES = new WasmException(this);
     break;
   }
   if (ES)

lib/CodeGen/AsmPrinter/CMakeLists.txt

@@ -23,6 +23,7 @@ add_llvm_library(LLVMAsmPrinter
   WinCFGuard.cpp
   WinException.cpp
   CodeViewDebug.cpp
+  WasmException.cpp
 
   DEPENDS
   intrinsics_gen

lib/CodeGen/AsmPrinter/EHStreamer.cpp

@@ -345,7 +345,9 @@ computeCallSiteTable(SmallVectorImpl<CallSiteEntry> &CallSites,
 ///     unwound and handling continues.
 ///  3. Type ID table contains references to all the C++ typeinfo for all
 ///     catches in the function.  This tables is reverse indexed base 1.
-void EHStreamer::emitExceptionTable() {
+///
+/// Returns the starting symbol of an exception table.
+MCSymbol *EHStreamer::emitExceptionTable() {
   const MachineFunction *MF = Asm->MF;
   const std::vector<const GlobalValue *> &TypeInfos = MF->getTypeInfos();
   const std::vector<unsigned> &FilterIds = MF->getFilterIds();
@@ -375,6 +377,7 @@ void EHStreamer::emitExceptionTable() {
   computeCallSiteTable(CallSites, LandingPads, FirstActions);
 
   bool IsSJLJ = Asm->MAI->getExceptionHandlingType() == ExceptionHandling::SjLj;
+  bool IsWasm = Asm->MAI->getExceptionHandlingType() == ExceptionHandling::Wasm;
   unsigned CallSiteEncoding =
       IsSJLJ ? dwarf::DW_EH_PE_udata4 : dwarf::DW_EH_PE_uleb128;
   bool HaveTTData = !TypeInfos.empty() || !FilterIds.empty();
@@ -457,8 +460,8 @@ void EHStreamer::emitExceptionTable() {
   Asm->EmitLabelDifferenceAsULEB128(CstEndLabel, CstBeginLabel);
   Asm->OutStreamer->EmitLabel(CstBeginLabel);
 
-  // SjLj Exception handling
-  if (IsSJLJ) {
+  // SjLj / Wasm Exception handling
+  if (IsSJLJ || IsWasm) {
     unsigned idx = 0;
     for (SmallVectorImpl<CallSiteEntry>::const_iterator
          I = CallSites.begin(), E = CallSites.end(); I != E; ++I, ++idx) {
@@ -604,6 +607,7 @@ void EHStreamer::emitExceptionTable() {
   }
 
   Asm->EmitAlignment(2);
+  return GCCETSym;
 }
 
 void EHStreamer::emitTypeInfos(unsigned TTypeEncoding, MCSymbol *TTBaseLabel) {

lib/CodeGen/AsmPrinter/EHStreamer.h

@@ -85,9 +85,10 @@ protected:
   /// zero for the landing pad and the action.  Calls marked 'nounwind' have
   /// no entry and must not be contained in the try-range of any entry - they
   /// form gaps in the table.  Entries must be ordered by try-range address.
-  void computeCallSiteTable(SmallVectorImpl<CallSiteEntry> &CallSites,
-                            const SmallVectorImpl<const LandingPadInfo *> &LandingPads,
-                            const SmallVectorImpl<unsigned> &FirstActions);
+  virtual void computeCallSiteTable(
+      SmallVectorImpl<CallSiteEntry> &CallSites,
+      const SmallVectorImpl<const LandingPadInfo *> &LandingPads,
+      const SmallVectorImpl<unsigned> &FirstActions);
 
   /// Emit landing pads and actions.
   ///
@@ -108,7 +109,9 @@ protected:
   ///     found the frame is unwound and handling continues.
   ///  3. Type id table contains references to all the C++ typeinfo for all
   ///     catches in the function.  This tables is reversed indexed base 1.
-  void emitExceptionTable();
+  ///
+  /// Returns the starting symbol of an exception table.
+  MCSymbol *emitExceptionTable();
 
   virtual void emitTypeInfos(unsigned TTypeEncoding, MCSymbol *TTBaseLabel);
 

lib/CodeGen/AsmPrinter/WasmException.cpp

@@ -0,0 +1,81 @@
+//===-- CodeGen/AsmPrinter/WasmException.cpp - Wasm Exception Impl --------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This file contains support for writing WebAssembly exception info into asm
+// files.
+//
+//===----------------------------------------------------------------------===//
+
+#include "WasmException.h"
+#include "llvm/MC/MCStreamer.h"
+using namespace llvm;
+
+void WasmException::markFunctionEnd() {
+  // Get rid of any dead landing pads.
+  if (!Asm->MF->getLandingPads().empty()) {
+    auto *NonConstMF = const_cast<MachineFunction *>(Asm->MF);
+    // Wasm does not set BeginLabel and EndLabel information for landing pads,
+    // so we should set the second argument false.
+    NonConstMF->tidyLandingPads(nullptr, /* TidyIfNoBeginLabels */ false);
+  }
+}
+
+void WasmException::endFunction(const MachineFunction *MF) {
+  bool ShouldEmitExceptionTable = false;
+  for (const LandingPadInfo &Info : MF->getLandingPads()) {
+    if (MF->hasWasmLandingPadIndex(Info.LandingPadBlock)) {
+      ShouldEmitExceptionTable = true;
+      break;
+    }
+  }
+  if (!ShouldEmitExceptionTable)
+    return;
+  MCSymbol *LSDALabel = emitExceptionTable();
+  assert(LSDALabel && ".GCC_exception_table has not been emitted!");
+
+  // Wasm requires every data section symbol to have a .size set. So we emit an
+  // end marker and set the size as the difference between the start end the end
+  // marker.
+  MCSymbol *LSDAEndLabel = Asm->createTempSymbol("GCC_except_table_end");
+  Asm->OutStreamer->EmitLabel(LSDAEndLabel);
+  MCContext &OutContext = Asm->OutStreamer->getContext();
+  const MCExpr *SizeExp = MCBinaryExpr::createSub(
+      MCSymbolRefExpr::create(LSDAEndLabel, OutContext),
+      MCSymbolRefExpr::create(LSDALabel, OutContext), OutContext);
+  Asm->OutStreamer->emitELFSize(LSDALabel, SizeExp);
+}
+
+// Compute the call-site table for wasm EH. Even though we use the same function
+// name to share the common routines, a call site entry in the table corresponds
+// to not a call site for possibly-throwing functions but a landing pad. In wasm
+// EH the VM is responsible for stack unwinding. After an exception occurs and
+// the stack is unwound, the control flow is transferred to wasm 'catch'
+// instruction by the VM, after which the personality function is called from
+// the compiler-generated code. Refer to WasmEHPrepare pass for more
+// information.
+void WasmException::computeCallSiteTable(
+    SmallVectorImpl<CallSiteEntry> &CallSites,
+    const SmallVectorImpl<const LandingPadInfo *> &LandingPads,
+    const SmallVectorImpl<unsigned> &FirstActions) {
+  MachineFunction &MF = *Asm->MF;
+  for (unsigned I = 0, N = LandingPads.size(); I < N; ++I) {
+    const LandingPadInfo *Info = LandingPads[I];
+    MachineBasicBlock *LPad = Info->LandingPadBlock;
+    // We don't emit LSDA for single catch (...).
+    if (!MF.hasWasmLandingPadIndex(LPad))
+      continue;
+    // Wasm EH must maintain the EH pads in the order assigned to them by the
+    // WasmEHPrepare pass.
+    unsigned LPadIndex = MF.getWasmLandingPadIndex(LPad);
+    CallSiteEntry Site = {nullptr, nullptr, Info, FirstActions[I]};
+    if (CallSites.size() < LPadIndex + 1)
+      CallSites.resize(LPadIndex + 1);
+    CallSites[LPadIndex] = Site;
+  }
+}

lib/CodeGen/AsmPrinter/WasmException.h

@@ -0,0 +1,42 @@
+//===-- WasmException.h - Wasm Exception Framework -------------*- C++ -*--===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This file contains support for writing WebAssembly exception info into asm
+// files.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_LIB_CODEGEN_ASMPRINTER_WASMEXCEPTION_H
+#define LLVM_LIB_CODEGEN_ASMPRINTER_WASMEXCEPTION_H
+
+#include "EHStreamer.h"
+#include "llvm/CodeGen/AsmPrinter.h"
+
+namespace llvm {
+
+class LLVM_LIBRARY_VISIBILITY WasmException : public EHStreamer {
+public:
+  WasmException(AsmPrinter *A) : EHStreamer(A) {}
+
+  void endModule() override {}
+  void beginFunction(const MachineFunction *MF) override {}
+  virtual void markFunctionEnd() override;
+  void endFunction(const MachineFunction *MF) override;
+
+protected:
+  // Compute the call site table for wasm EH.
+  void computeCallSiteTable(
+      SmallVectorImpl<CallSiteEntry> &CallSites,
+      const SmallVectorImpl<const LandingPadInfo *> &LandingPads,
+      const SmallVectorImpl<unsigned> &FirstActions) override;
+};
+
+} // End of namespace llvm
+
+#endif

lib/CodeGen/MachineFunction.cpp

@@ -661,8 +661,11 @@ MCSymbol *MachineFunction::addLandingPad(MachineBasicBlock *LandingPad) {
       }
     }
 
-  } else if (isa<CatchPadInst>(FirstI)) {
-    // TODO
+  } else if (const auto *CPI = dyn_cast<CatchPadInst>(FirstI)) {
+    for (unsigned I = CPI->getNumArgOperands(); I != 0; --I) {
+      Value *TypeInfo = CPI->getArgOperand(I - 1)->stripPointerCasts();
+      addCatchTypeInfo(LandingPad, dyn_cast<GlobalValue>(TypeInfo));
+    }
 
   } else {
     assert(isa<CleanupPadInst>(FirstI) && "Invalid landingpad!");
@@ -687,7 +690,8 @@ void MachineFunction::addFilterTypeInfo(MachineBasicBlock *LandingPad,
   LP.TypeIds.push_back(getFilterIDFor(IdsInFilter));
 }
 
-void MachineFunction::tidyLandingPads(DenseMap<MCSymbol*, uintptr_t> *LPMap) {
+void MachineFunction::tidyLandingPads(DenseMap<MCSymbol *, uintptr_t> *LPMap,
+                                      bool TidyIfNoBeginLabels) {
   for (unsigned i = 0; i != LandingPads.size(); ) {
     LandingPadInfo &LandingPad = LandingPads[i];
     if (LandingPad.LandingPadLabel &&
@@ -702,24 +706,25 @@ void MachineFunction::tidyLandingPads(DenseMap<MCSymbol*, uintptr_t> *LPMap) {
       continue;
     }
 
-    for (unsigned j = 0, e = LandingPads[i].BeginLabels.size(); j != e; ++j) {
-      MCSymbol *BeginLabel = LandingPad.BeginLabels[j];
-      MCSymbol *EndLabel = LandingPad.EndLabels[j];
-      if ((BeginLabel->isDefined() ||
-           (LPMap && (*LPMap)[BeginLabel] != 0)) &&
-          (EndLabel->isDefined() ||
-           (LPMap && (*LPMap)[EndLabel] != 0))) continue;
-
-      LandingPad.BeginLabels.erase(LandingPad.BeginLabels.begin() + j);
-      LandingPad.EndLabels.erase(LandingPad.EndLabels.begin() + j);
-      --j;
-      --e;
-    }
+    if (TidyIfNoBeginLabels) {
+      for (unsigned j = 0, e = LandingPads[i].BeginLabels.size(); j != e; ++j) {
+        MCSymbol *BeginLabel = LandingPad.BeginLabels[j];
+        MCSymbol *EndLabel = LandingPad.EndLabels[j];
+        if ((BeginLabel->isDefined() || (LPMap && (*LPMap)[BeginLabel] != 0)) &&
+            (EndLabel->isDefined() || (LPMap && (*LPMap)[EndLabel] != 0)))
+          continue;
+
+        LandingPad.BeginLabels.erase(LandingPad.BeginLabels.begin() + j);
+        LandingPad.EndLabels.erase(LandingPad.EndLabels.begin() + j);
+        --j;
+        --e;
+      }
 
-    // Remove landing pads with no try-ranges.
-    if (LandingPads[i].BeginLabels.empty()) {
-      LandingPads.erase(LandingPads.begin() + i);
-      continue;
+      // Remove landing pads with no try-ranges.
+      if (LandingPads[i].BeginLabels.empty()) {
+        LandingPads.erase(LandingPads.begin() + i);
+        continue;
+      }
     }
 
     // If there is no landing pad, ensure that the list of typeids is empty.

lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp

@@ -6294,12 +6294,12 @@ SelectionDAGBuilder::visitIntrinsicCall(const CallInst &I, unsigned Intrinsic) {
     return nullptr;
   }
 
-  case Intrinsic::wasm_landingpad_index: {
-    // TODO store landing pad index in a map, which will be used when generating
-    // LSDA information
+  case Intrinsic::wasm_landingpad_index:
+    // Information this intrinsic contained has been transferred to
+    // MachineFunction in SelectionDAGISel::PrepareEHLandingPad. We can safely
+    // delete it now.
     return nullptr;
   }
-  }
 }
 
 void SelectionDAGBuilder::visitConstrainedFPIntrinsic(
@@ -6456,7 +6456,7 @@ SelectionDAGBuilder::lowerInvokable(TargetLowering::CallLoweringInfo &CLI,
       WinEHFuncInfo *EHInfo = DAG.getMachineFunction().getWinEHFuncInfo();
       EHInfo->addIPToStateRange(cast<InvokeInst>(CLI.CS.getInstruction()),
                                 BeginLabel, EndLabel);
-    } else {
+    } else if (!isScopedEHPersonality(Pers)) {
       MF.addInvoke(FuncInfo.MBBMap[EHPadBB], BeginLabel, EndLabel);
     }
   }

lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp

@@ -27,6 +27,7 @@
 #include "llvm/Analysis/AliasAnalysis.h"
 #include "llvm/Analysis/BranchProbabilityInfo.h"
 #include "llvm/Analysis/CFG.h"
+#include "llvm/Analysis/EHPersonalities.h"
 #include "llvm/Analysis/OptimizationRemarkEmitter.h"
 #include "llvm/Analysis/TargetLibraryInfo.h"
 #include "llvm/Analysis/TargetTransformInfo.h"
@@ -1128,6 +1129,36 @@ static bool hasExceptionPointerOrCodeUser(const CatchPadInst *CPI) {
   return false;
 }
 
+// wasm.landingpad.index intrinsic is for associating a landing pad index number
+// with a catchpad instruction. Retrieve the landing pad index in the intrinsic
+// and store the mapping in the function.
+static void mapWasmLandingPadIndex(MachineBasicBlock *MBB,
+                                   const CatchPadInst *CPI) {
+  MachineFunction *MF = MBB->getParent();
+  // In case of single catch (...), we don't emit LSDA, so we don't need
+  // this information.
+  bool IsSingleCatchAllClause =
+      CPI->getNumArgOperands() == 1 &&
+      cast<Constant>(CPI->getArgOperand(0))->isNullValue();
+  if (!IsSingleCatchAllClause) {
+    // Create a mapping from landing pad label to landing pad index.
+    bool IntrFound = false;
+    for (const User *U : CPI->users()) {
+      if (const auto *Call = dyn_cast<IntrinsicInst>(U)) {
+        Intrinsic::ID IID = Call->getIntrinsicID();
+        if (IID == Intrinsic::wasm_landingpad_index) {
+          Value *IndexArg = Call->getArgOperand(1);
+          int Index = cast<ConstantInt>(IndexArg)->getZExtValue();
+          MF->setWasmLandingPadIndex(MBB, Index);
+          IntrFound = true;
+          break;
+        }
+      }
+    }
+    assert(IntrFound && "wasm.landingpad.index intrinsic not found!");
+  }
+}
+
 /// PrepareEHLandingPad - Emit an EH_LABEL, set up live-in registers, and
 /// do other setup for EH landing-pad blocks.
 bool SelectionDAGISel::PrepareEHLandingPad() {
@@ -1137,44 +1168,48 @@ bool SelectionDAGISel::PrepareEHLandingPad() {
   const TargetRegisterClass *PtrRC =
       TLI->getRegClassFor(TLI->getPointerTy(CurDAG->getDataLayout()));
 
+  auto Pers = classifyEHPersonality(PersonalityFn);
+
   // Catchpads have one live-in register, which typically holds the exception
   // pointer or code.
-  if (const auto *CPI = dyn_cast<CatchPadInst>(LLVMBB->getFirstNonPHI())) {
-    if (hasExceptionPointerOrCodeUser(CPI)) {
-      // Get or create the virtual register to hold the pointer or code.  Mark
-      // the live in physreg and copy into the vreg.
-      MCPhysReg EHPhysReg = TLI->getExceptionPointerRegister(PersonalityFn);
-      assert(EHPhysReg && "target lacks exception pointer register");
-      MBB->addLiveIn(EHPhysReg);
-      unsigned VReg = FuncInfo->getCatchPadExceptionPointerVReg(CPI, PtrRC);
-      BuildMI(*MBB, FuncInfo->InsertPt, SDB->getCurDebugLoc(),
-              TII->get(TargetOpcode::COPY), VReg)
-          .addReg(EHPhysReg, RegState::Kill);
+  if (isFuncletEHPersonality(Pers)) {
+    if (const auto *CPI = dyn_cast<CatchPadInst>(LLVMBB->getFirstNonPHI())) {
+      if (hasExceptionPointerOrCodeUser(CPI)) {
+        // Get or create the virtual register to hold the pointer or code.  Mark
+        // the live in physreg and copy into the vreg.
+        MCPhysReg EHPhysReg = TLI->getExceptionPointerRegister(PersonalityFn);
+        assert(EHPhysReg && "target lacks exception pointer register");
+        MBB->addLiveIn(EHPhysReg);
+        unsigned VReg = FuncInfo->getCatchPadExceptionPointerVReg(CPI, PtrRC);
+        BuildMI(*MBB, FuncInfo->InsertPt, SDB->getCurDebugLoc(),
+                TII->get(TargetOpcode::COPY), VReg)
+            .addReg(EHPhysReg, RegState::Kill);
+      }
     }
     return true;
   }
 
-  if (!LLVMBB->isLandingPad())
-    return true;
-
   // Add a label to mark the beginning of the landing pad.  Deletion of the
   // landing pad can thus be detected via the MachineModuleInfo.
   MCSymbol *Label = MF->addLandingPad(MBB);
 
-  // Assign the call site to the landing pad's begin label.
-  MF->setCallSiteLandingPad(Label, SDB->LPadToCallSiteMap[MBB]);
-
   const MCInstrDesc &II = TII->get(TargetOpcode::EH_LABEL);
   BuildMI(*MBB, FuncInfo->InsertPt, SDB->getCurDebugLoc(), II)
     .addSym(Label);
 
-  // Mark exception register as live in.
-  if (unsigned Reg = TLI->getExceptionPointerRegister(PersonalityFn))
-    FuncInfo->ExceptionPointerVirtReg = MBB->addLiveIn(Reg, PtrRC);
-
-  // Mark exception selector register as live in.
-  if (unsigned Reg = TLI->getExceptionSelectorRegister(PersonalityFn))
-    FuncInfo->ExceptionSelectorVirtReg = MBB->addLiveIn(Reg, PtrRC);
+  if (Pers == EHPersonality::Wasm_CXX) {
+    if (const auto *CPI = dyn_cast<CatchPadInst>(LLVMBB->getFirstNonPHI()))
+      mapWasmLandingPadIndex(MBB, CPI);
+  } else {
+    // Assign the call site to the landing pad's begin label.
+    MF->setCallSiteLandingPad(Label, SDB->LPadToCallSiteMap[MBB]);
+    // Mark exception register as live in.
+    if (unsigned Reg = TLI->getExceptionPointerRegister(PersonalityFn))
+      FuncInfo->ExceptionPointerVirtReg = MBB->addLiveIn(Reg, PtrRC);
+    // Mark exception selector register as live in.
+    if (unsigned Reg = TLI->getExceptionSelectorRegister(PersonalityFn))
+      FuncInfo->ExceptionSelectorVirtReg = MBB->addLiveIn(Reg, PtrRC);
+  }
 
   return true;
 }

lib/CodeGen/TargetLoweringObjectFileImpl.cpp

@@ -1748,6 +1748,10 @@ const MCExpr *TargetLoweringObjectFileWasm::lowerRelativeReference(
 void TargetLoweringObjectFileWasm::InitializeWasm() {
   StaticCtorSection =
       getContext().getWasmSection(".init_array", SectionKind::getData());
+
+  // We don't use PersonalityEncoding and LSDAEncoding because we don't emit
+  // .cfi directives. We use TTypeEncoding to encode typeinfo global variables.
+  TTypeEncoding = dwarf::DW_EH_PE_absptr;
 }
 
 MCSection *TargetLoweringObjectFileWasm::getStaticCtorSection(

lib/CodeGen/WasmEHPrepare.cpp

@@ -300,7 +300,7 @@ void WasmEHPrepare::prepareEHPad(BasicBlock *BB, unsigned Index) {
   // This is to create a map of <landingpad EH label, landingpad index> in
   // SelectionDAGISel, which is to be used in EHStreamer to emit LSDA tables.
   // Pseudocode: wasm.landingpad.index(Index);
-  IRB.CreateCall(LPadIndexF, IRB.getInt32(Index));
+  IRB.CreateCall(LPadIndexF, {FPI, IRB.getInt32(Index)});
 
   // Pseudocode: __wasm_lpad_context.lpad_index = index;
   IRB.CreateStore(IRB.getInt32(Index), LPadIndexField);

lib/MC/MCObjectFileInfo.cpp

@@ -746,6 +746,12 @@ void MCObjectFileInfo::initWasmMCObjectFileInfo(const Triple &T) {
   DwarfPubNamesSection = Ctx->getWasmSection(".debug_pubnames", SectionKind::getMetadata());
   DwarfPubTypesSection = Ctx->getWasmSection(".debug_pubtypes", SectionKind::getMetadata());
 
+  // Wasm use data section for LSDA.
+  // TODO Consider putting each function's exception table in a separate
+  // section, as in -function-sections, to facilitate lld's --gc-section.
+  LSDASection = Ctx->getWasmSection(".rodata.gcc_except_table",
+                                    SectionKind::getReadOnlyWithRel());
+
   // TODO: Define more sections.
 }
 

lib/MC/WasmObjectWriter.cpp

@@ -635,10 +635,12 @@ static void addData(SmallVectorImpl<char> &DataBytes,
         llvm_unreachable("The fill should be an assembler constant");
       DataBytes.insert(DataBytes.end(), Fill->getValueSize() * NumValues,
                        Fill->getValue());
+    } else if (auto *LEB = dyn_cast<MCLEBFragment>(&Frag)) {
+      const SmallVectorImpl<char> &Contents = LEB->getContents();
+      DataBytes.insert(DataBytes.end(), Contents.begin(), Contents.end());
     } else {
       const auto &DataFrag = cast<MCDataFragment>(Frag);
       const SmallVectorImpl<char> &Contents = DataFrag.getContents();
-
       DataBytes.insert(DataBytes.end(), Contents.begin(), Contents.end());
     }
   }

lib/Target/WebAssembly/WebAssemblyISelLowering.cpp

@@ -21,6 +21,7 @@
 #include "llvm/CodeGen/CallingConvLower.h"
 #include "llvm/CodeGen/MachineInstrBuilder.h"
 #include "llvm/CodeGen/MachineJumpTableInfo.h"
+#include "llvm/CodeGen/MachineModuleInfo.h"
 #include "llvm/CodeGen/MachineRegisterInfo.h"
 #include "llvm/CodeGen/SelectionDAG.h"
 #include "llvm/IR/DiagnosticInfo.h"
@@ -998,9 +999,17 @@ WebAssemblyTargetLowering::LowerINTRINSIC_WO_CHAIN(SDValue Op,
   default:
     return {}; // Don't custom lower most intrinsics.
 
-  case Intrinsic::wasm_lsda:
-    // TODO For now, just return 0 not to crash
-    return DAG.getConstant(0, DL, Op.getValueType());
+  case Intrinsic::wasm_lsda: {
+    MachineFunction &MF = DAG.getMachineFunction();
+    EVT VT = Op.getValueType();
+    const TargetLowering &TLI = DAG.getTargetLoweringInfo();
+    MVT PtrVT = TLI.getPointerTy(DAG.getDataLayout());
+    auto &Context = MF.getMMI().getContext();
+    MCSymbol *S = Context.getOrCreateSymbol(Twine("GCC_except_table") +
+                                            Twine(MF.getFunctionNumber()));
+    return DAG.getNode(WebAssemblyISD::Wrapper, DL, VT,
+                       DAG.getMCSymbol(S, PtrVT));
+  }
   }
 }
 

lib/Target/WebAssembly/WebAssemblyInstrInfo.td

@@ -282,6 +282,8 @@ def : Pat<(i32 (WebAssemblywrapper tglobaladdr:$addr)),
           (CONST_I32 tglobaladdr:$addr)>;
 def : Pat<(i32 (WebAssemblywrapper texternalsym:$addr)),
           (CONST_I32 texternalsym:$addr)>;
+def : Pat<(i32 (WebAssemblywrapper mcsym:$sym)), (CONST_I32 mcsym:$sym)>;
+def : Pat<(i64 (WebAssemblywrapper mcsym:$sym)), (CONST_I64 mcsym:$sym)>;
 
 //===----------------------------------------------------------------------===//
 // Additional sets of instructions.

lib/Target/WebAssembly/WebAssemblyMCInstLower.cpp

@@ -230,6 +230,13 @@ void WebAssemblyMCInstLower::Lower(const MachineInstr *MI,
           (MO.getTargetFlags() & WebAssemblyII::MO_SYMBOL_FUNCTION) != 0,
           (MO.getTargetFlags() & WebAssemblyII::MO_SYMBOL_GLOBAL) != 0);
       break;
+    case MachineOperand::MO_MCSymbol:
+      // This is currently used only for LSDA symbols (GCC_except_table),
+      // because global addresses or other external symbols are handled above.
+      assert(MO.getTargetFlags() == 0 &&
+             "WebAssembly does not use target flags on MCSymbol");
+      MCOp = LowerSymbolOperand(MO.getMCSymbol(), /*Offset=*/0, false, false);
+      break;
     }
 
     OutMI.addOperand(MCOp);

test/CodeGen/WebAssembly/eh-lsda.ll

@@ -0,0 +1,239 @@
+; RUN: llc < %s -disable-wasm-fallthrough-return-opt -wasm-keep-registers -exception-model=wasm -mattr=+exception-handling | FileCheck -allow-deprecated-dag-overlap %s
+target datalayout = "e-m:e-p:32:32-i64:64-n32:64-S128"
+target triple = "wasm32-unknown-unknown"
+
+@_ZTIi = external constant i8*
+@_ZTIf = external constant i8*
+@_ZTId = external constant i8*
+
+; Single catch (...) does not need an exception table.
+;
+; try {
+;   may_throw();
+; } catch (...) {
+; }
+; CHECK-LABEL: test0:
+; CHECK-NOT: GCC_except_table
+define void @test0() personality i8* bitcast (i32 (...)* @__gxx_wasm_personality_v0 to i8*) {
+entry:
+  invoke void @may_throw()
+          to label %try.cont unwind label %catch.dispatch
+
+catch.dispatch:                                   ; preds = %entry
+  %0 = catchswitch within none [label %catch.start] unwind to caller
+
+catch.start:                                      ; preds = %catch.dispatch
+  %1 = catchpad within %0 [i8* null]
+  %2 = call i8* @llvm.wasm.get.exception(token %1)
+  %3 = call i32 @llvm.wasm.get.ehselector(token %1)
+  %4 = call i8* @__cxa_begin_catch(i8* %2) [ "funclet"(token %1) ]
+  call void @__cxa_end_catch() [ "funclet"(token %1) ]
+  catchret from %1 to label %try.cont
+
+try.cont:                                         ; preds = %entry, %catch.start
+  ret void
+}
+
+; Exception table generation + shared action test.
+;
+; try {
+;   may_throw();
+; } catch (int) {
+; } catch (float) {
+; } catch (double) {
+; } catch (...) {
+; }
+;
+; try {
+;   may_throw();
+; } catch (double) {
+; } catch (...) {
+; }
+;
+; try {
+;   may_throw();
+; } catch (int) {
+; } catch (float) {
+; }
+;
+; There are three landing pads. The second landing pad should share action table
+; entries with the first landing pad because they end with the same sequence
+; (double -> ...). But the third landing table cannot share action table entries
+; with others, so it should create its own entries.
+; CHECK-LABEL: test1:
+; CHECK: .section  .rodata.gcc_except_table,"",@
+; CHECK-NEXT:   .p2align  2
+; CHECK-NEXT: GCC_except_table[[START:[0-9]+]]:
+; CHECK-NEXT: .Lexception0:
+; CHECK-NEXT:   .int8  255                     # @LPStart Encoding = omit
+; CHECK-NEXT:   .int8  0                       # @TType Encoding = absptr
+; CHECK-NEXT:   .uleb128 .Lttbase0-.Lttbaseref0
+; CHECK-NEXT: .Lttbaseref0:
+; CHECK-NEXT:   .int8  1                       # Call site Encoding = uleb128
+; CHECK-NEXT:   .uleb128 .Lcst_end0-.Lcst_begin0
+; CHECK-NEXT: .Lcst_begin0:
+; CHECK-NEXT:   .int8  0                       # >> Call Site 0 <<
+; CHECK-NEXT:                                  #   On exception at call site 0
+; CHECK-NEXT:   .int8  7                       #   Action: 4
+; CHECK-NEXT:   .int8  1                       # >> Call Site 1 <<
+; CHECK-NEXT:                                  #   On exception at call site 1
+; CHECK-NEXT:   .int8  3                       #   Action: 2
+; CHECK-NEXT:   .int8  2                       # >> Call Site 2 <<
+; CHECK-NEXT:                                  #   On exception at call site 2
+; CHECK-NEXT:   .int8  11                      #   Action: 6
+; CHECK-NEXT: .Lcst_end0:
+; CHECK-NEXT:   .int8  1                       # >> Action Record 1 <<
+; CHECK-NEXT:                                  #   Catch TypeInfo 1
+; CHECK-NEXT:   .int8  0                       #   No further actions
+; CHECK-NEXT:   .int8  2                       # >> Action Record 2 <<
+; CHECK-NEXT:                                  #   Catch TypeInfo 2
+; CHECK-NEXT:   .int8  125                     #   Continue to action 1
+; CHECK-NEXT:   .int8  3                       # >> Action Record 3 <<
+; CHECK-NEXT:                                  #   Catch TypeInfo 3
+; CHECK-NEXT:   .int8  125                     #   Continue to action 2
+; CHECK-NEXT:   .int8  4                       # >> Action Record 4 <<
+; CHECK-NEXT:                                  #   Catch TypeInfo 4
+; CHECK-NEXT:   .int8  125                     #   Continue to action 3
+; CHECK-NEXT:   .int8  3                       # >> Action Record 5 <<
+; CHECK-NEXT:                                  #   Catch TypeInfo 3
+; CHECK-NEXT:   .int8  0                       #   No further actions
+; CHECK-NEXT:   .int8  4                       # >> Action Record 6 <<
+; CHECK-NEXT:                                  #   Catch TypeInfo 4
+; CHECK-NEXT:   .int8  125                     #   Continue to action 5
+; CHECK-NEXT:   .p2align  2
+; CHECK-NEXT:                                  # >> Catch TypeInfos <<
+; CHECK-NEXT:   .int32  _ZTIi                  # TypeInfo 4
+; CHECK-NEXT:   .int32  _ZTIf                  # TypeInfo 3
+; CHECK-NEXT:   .int32  _ZTId                  # TypeInfo 2
+; CHECK-NEXT:   .int32  0                      # TypeInfo 1
+; CHECK-NEXT: .Lttbase0:
+; CHECK-NEXT:   .p2align  2
+; CHECK-NEXT: .LGCC_except_table_end[[END:[0-9]+]]:
+; CHECK-NEXT:   .size  GCC_except_table[[START]], .LGCC_except_table_end[[END]]-GCC_except_table[[START]]
+define void @test1() personality i8* bitcast (i32 (...)* @__gxx_wasm_personality_v0 to i8*) {
+entry:
+  invoke void @may_throw()
+          to label %try.cont unwind label %catch.dispatch
+
+catch.dispatch:                                   ; preds = %entry
+  %0 = catchswitch within none [label %catch.start] unwind to caller
+
+catch.start:                                      ; preds = %catch.dispatch
+  %1 = catchpad within %0 [i8* bitcast (i8** @_ZTIi to i8*), i8* bitcast (i8** @_ZTIf to i8*), i8* bitcast (i8** @_ZTId to i8*), i8* null]
+  %2 = call i8* @llvm.wasm.get.exception(token %1)
+  %3 = call i32 @llvm.wasm.get.ehselector(token %1)
+  %4 = call i32 @llvm.eh.typeid.for(i8* bitcast (i8** @_ZTIi to i8*))
+  %matches = icmp eq i32 %3, %4
+  br i1 %matches, label %catch10, label %catch.fallthrough
+
+catch10:                                          ; preds = %catch.start
+  %5 = call i8* @__cxa_begin_catch(i8* %2) [ "funclet"(token %1) ]
+  %6 = bitcast i8* %5 to i32*
+  %7 = load i32, i32* %6, align 4
+  call void @__cxa_end_catch() [ "funclet"(token %1) ]
+  catchret from %1 to label %try.cont
+
+try.cont:                                         ; preds = %entry, %catch, %catch4, %catch7, %catch10
+  invoke void @may_throw()
+          to label %try.cont23 unwind label %catch.dispatch14
+
+catch.dispatch14:                                 ; preds = %try.cont
+  %8 = catchswitch within none [label %catch.start15] unwind to caller
+
+catch.start15:                                    ; preds = %catch.dispatch14
+  %9 = catchpad within %8 [i8* bitcast (i8** @_ZTId to i8*), i8* null]
+  %10 = call i8* @llvm.wasm.get.exception(token %9)
+  %11 = call i32 @llvm.wasm.get.ehselector(token %9)
+  %12 = call i32 @llvm.eh.typeid.for(i8* bitcast (i8** @_ZTId to i8*))
+  %matches16 = icmp eq i32 %11, %12
+  %13 = call i8* @__cxa_begin_catch(i8* %10) [ "funclet"(token %9) ]
+  br i1 %matches16, label %catch20, label %catch17
+
+catch20:                                          ; preds = %catch.start15
+  %14 = bitcast i8* %13 to double*
+  %15 = load double, double* %14, align 8
+  call void @__cxa_end_catch() [ "funclet"(token %9) ]
+  catchret from %9 to label %try.cont23
+
+try.cont23:                                       ; preds = %try.cont, %catch17, %catch20
+  invoke void @may_throw()
+          to label %try.cont36 unwind label %catch.dispatch25
+
+catch.dispatch25:                                 ; preds = %try.cont23
+  %16 = catchswitch within none [label %catch.start26] unwind to caller
+
+catch.start26:                                    ; preds = %catch.dispatch25
+  %17 = catchpad within %16 [i8* bitcast (i8** @_ZTIi to i8*), i8* bitcast (i8** @_ZTIf to i8*)]
+  %18 = call i8* @llvm.wasm.get.exception(token %17)
+  %19 = call i32 @llvm.wasm.get.ehselector(token %17)
+  %20 = call i32 @llvm.eh.typeid.for(i8* bitcast (i8** @_ZTIi to i8*))
+  %matches27 = icmp eq i32 %19, %20
+  br i1 %matches27, label %catch33, label %catch.fallthrough28
+
+catch33:                                          ; preds = %catch.start26
+  %21 = call i8* @__cxa_begin_catch(i8* %18) [ "funclet"(token %17) ]
+  %22 = bitcast i8* %21 to i32*
+  %23 = load i32, i32* %22, align 4
+  call void @__cxa_end_catch() [ "funclet"(token %17) ]
+  catchret from %17 to label %try.cont36
+
+catch.fallthrough28:                              ; preds = %catch.start26
+  %24 = call i32 @llvm.eh.typeid.for(i8* bitcast (i8** @_ZTIf to i8*))
+  %matches29 = icmp eq i32 %19, %24
+  br i1 %matches29, label %catch30, label %rethrow
+
+catch30:                                          ; preds = %catch.fallthrough28
+  %25 = call i8* @__cxa_begin_catch(i8* %18) [ "funclet"(token %17) ]
+  %26 = bitcast i8* %25 to float*
+  %27 = load float, float* %26, align 4
+  call void @__cxa_end_catch() [ "funclet"(token %17) ]
+  catchret from %17 to label %try.cont36
+
+rethrow:                                          ; preds = %catch.fallthrough28
+  call void @__cxa_rethrow() [ "funclet"(token %17) ]
+  unreachable
+
+try.cont36:                                       ; preds = %try.cont23, %catch30, %catch33
+  ret void
+
+catch17:                                          ; preds = %catch.start15
+  call void @__cxa_end_catch() [ "funclet"(token %9) ]
+  catchret from %9 to label %try.cont23
+
+catch.fallthrough:                                ; preds = %catch.start
+  %28 = call i32 @llvm.eh.typeid.for(i8* bitcast (i8** @_ZTIf to i8*))
+  %matches1 = icmp eq i32 %3, %28
+  br i1 %matches1, label %catch7, label %catch.fallthrough2
+
+catch7:                                           ; preds = %catch.fallthrough
+  %29 = call i8* @__cxa_begin_catch(i8* %2) [ "funclet"(token %1) ]
+  %30 = bitcast i8* %29 to float*
+  %31 = load float, float* %30, align 4
+  call void @__cxa_end_catch() [ "funclet"(token %1) ]
+  catchret from %1 to label %try.cont
+
+catch.fallthrough2:                               ; preds = %catch.fallthrough
+  %32 = call i32 @llvm.eh.typeid.for(i8* bitcast (i8** @_ZTId to i8*))
+  %matches3 = icmp eq i32 %3, %32
+  %33 = call i8* @__cxa_begin_catch(i8* %2) [ "funclet"(token %1) ]
+  br i1 %matches3, label %catch4, label %catch
+
+catch4:                                           ; preds = %catch.fallthrough2
+  %34 = bitcast i8* %33 to double*
+  %35 = load double, double* %34, align 8
+  call void @__cxa_end_catch() [ "funclet"(token %1) ]
+  catchret from %1 to label %try.cont
+
+catch:                                            ; preds = %catch.fallthrough2
+  call void @__cxa_end_catch() [ "funclet"(token %1) ]
+  catchret from %1 to label %try.cont
+}
+
+declare void @may_throw()
+declare i32 @llvm.eh.typeid.for(i8*)
+declare i8* @llvm.wasm.get.exception(token)
+declare i32 @llvm.wasm.get.ehselector(token)
+declare void @__cxa_rethrow()
+declare i8* @__cxa_begin_catch(i8*)
+declare void @__cxa_end_catch()
+declare i32 @__gxx_wasm_personality_v0(...)

test/CodeGen/WebAssembly/wasmehprepare.ll

@@ -30,7 +30,7 @@ catch.start:                                      ; preds = %catch.dispatch
 ; CHECK: catch.start:
 ; CHECK-NEXT:   %[[CATCHPAD:.*]] = catchpad
 ; CHECK-NEXT:   %[[EXN:.*]] = call i8* @llvm.wasm.catch(i32 0)
-; CHECK-NEXT:   call void @llvm.wasm.landingpad.index(i32 0)
+; CHECK-NEXT:   call void @llvm.wasm.landingpad.index(token %[[CATCHPAD]], i32 0)
 ; CHECK-NEXT:   store i32 0, i32* getelementptr inbounds ({ i32, i8*, i32 }, { i32, i8*, i32 }* @__wasm_lpad_context, i32 0, i32 0)
 ; CHECK-NEXT:   %[[LSDA:.*]] = call i8* @llvm.wasm.lsda()
 ; CHECK-NEXT:   store i8* %[[LSDA]], i8** getelementptr inbounds ({ i32, i8*, i32 }, { i32, i8*, i32 }* @__wasm_lpad_context, i32 0, i32 1)
@@ -98,7 +98,7 @@ catch.start3:                                     ; preds = %catch.dispatch2
   %matches = icmp eq i32 %8, %9
   br i1 %matches, label %catch4, label %rethrow
 ; CHECK: catch.start3:
-; CHECK:   call void @llvm.wasm.landingpad.index(i32 0)
+; CHECK:   call void @llvm.wasm.landingpad.index(token %{{.+}}, i32 0)
 
 catch4:                                           ; preds = %catch.start3
   %10 = call i8* @__cxa_begin_catch(i8* %7) [ "funclet"(token %6) ]
@@ -311,7 +311,7 @@ declare void @__cxa_rethrow()
 declare void @__clang_call_terminate(i8*)
 
 ; CHECK-DAG: declare i8* @llvm.wasm.catch(i32)
-; CHECK-DAG: declare void @llvm.wasm.landingpad.index(i32)
+; CHECK-DAG: declare void @llvm.wasm.landingpad.index(token, i32)
 ; CHECK-DAG: declare i8* @llvm.wasm.lsda()
 ; CHECK-DAG: declare i32 @_Unwind_CallPersonality(i8*)