1 files changed, 267 insertions, 0 deletions
diff --git a/llvm/lib/CodeGen/DwarfEHPrepare.cpp b/llvm/lib/CodeGen/DwarfEHPrepare.cpp
new file mode 100644
index 000000000000..ddd6cec5a178
--- /dev/null
+++ b/llvm/lib/CodeGen/DwarfEHPrepare.cpp
@@ -0,0 +1,267 @@
+//===- DwarfEHPrepare - Prepare exception handling for code generation ----===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+//
+// This pass mulches exception handling code into a form adapted to code
+// generation. Required if using dwarf exception handling.
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/ADT/BitVector.h"
+#include "llvm/ADT/SmallVector.h"
+#include "llvm/ADT/Statistic.h"
+#include "llvm/Analysis/CFG.h"
+#include "llvm/Analysis/EHPersonalities.h"
+#include "llvm/Analysis/TargetTransformInfo.h"
+#include "llvm/Transforms/Utils/Local.h"
+#include "llvm/CodeGen/RuntimeLibcalls.h"
+#include "llvm/CodeGen/TargetLowering.h"
+#include "llvm/CodeGen/TargetPassConfig.h"
+#include "llvm/CodeGen/TargetSubtargetInfo.h"
+#include "llvm/IR/BasicBlock.h"
+#include "llvm/IR/Constants.h"
+#include "llvm/IR/DerivedTypes.h"
+#include "llvm/IR/Dominators.h"
+#include "llvm/IR/Function.h"
+#include "llvm/IR/Instructions.h"
+#include "llvm/IR/Module.h"
+#include "llvm/IR/Type.h"
+#include "llvm/Pass.h"
+#include "llvm/Support/Casting.h"
+#include "llvm/Target/TargetMachine.h"
+#include <cstddef>
+
+using namespace llvm;
+
+#define DEBUG_TYPE "dwarfehprepare"
+
+STATISTIC(NumResumesLowered, "Number of resume calls lowered");
+
+namespace {
+
+  class DwarfEHPrepare : public FunctionPass {
+    // RewindFunction - _Unwind_Resume or the target equivalent.
+    FunctionCallee RewindFunction = nullptr;
+
+    DominatorTree *DT = nullptr;
+    const TargetLowering *TLI = nullptr;
+
+    bool InsertUnwindResumeCalls(Function &Fn);
+    Value *GetExceptionObject(ResumeInst *RI);
+    size_t
+    pruneUnreachableResumes(Function &Fn,
+                            SmallVectorImpl<ResumeInst *> &Resumes,
+                            SmallVectorImpl<LandingPadInst *> &CleanupLPads);
+
+  public:
+    static char ID; // Pass identification, replacement for typeid.
+
+    DwarfEHPrepare() : FunctionPass(ID) {}
+
+    bool runOnFunction(Function &Fn) override;
+
+    bool doFinalization(Module &M) override {
+      RewindFunction = nullptr;
+      return false;
+    }
+
+    void getAnalysisUsage(AnalysisUsage &AU) const override;
+
+    StringRef getPassName() const override {
+      return "Exception handling preparation";
+    }
+  };
+
+} // end anonymous namespace
+
+char DwarfEHPrepare::ID = 0;
+
+INITIALIZE_PASS_BEGIN(DwarfEHPrepare, DEBUG_TYPE,
+                      "Prepare DWARF exceptions", false, false)
+INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)
+INITIALIZE_PASS_DEPENDENCY(TargetPassConfig)
+INITIALIZE_PASS_DEPENDENCY(TargetTransformInfoWrapperPass)
+INITIALIZE_PASS_END(DwarfEHPrepare, DEBUG_TYPE,
+                    "Prepare DWARF exceptions", false, false)
+
+FunctionPass *llvm::createDwarfEHPass() { return new DwarfEHPrepare(); }
+
+void DwarfEHPrepare::getAnalysisUsage(AnalysisUsage &AU) const {
+  AU.addRequired<TargetPassConfig>();
+  AU.addRequired<TargetTransformInfoWrapperPass>();
+  AU.addRequired<DominatorTreeWrapperPass>();
+}
+
+/// GetExceptionObject - Return the exception object from the value passed into
+/// the 'resume' instruction (typically an aggregate). Clean up any dead
+/// instructions, including the 'resume' instruction.
+Value *DwarfEHPrepare::GetExceptionObject(ResumeInst *RI) {
+  Value *V = RI->getOperand(0);
+  Value *ExnObj = nullptr;
+  InsertValueInst *SelIVI = dyn_cast<InsertValueInst>(V);
+  LoadInst *SelLoad = nullptr;
+  InsertValueInst *ExcIVI = nullptr;
+  bool EraseIVIs = false;
+
+  if (SelIVI) {
+    if (SelIVI->getNumIndices() == 1 && *SelIVI->idx_begin() == 1) {
+      ExcIVI = dyn_cast<InsertValueInst>(SelIVI->getOperand(0));
+      if (ExcIVI && isa<UndefValue>(ExcIVI->getOperand(0)) &&
+          ExcIVI->getNumIndices() == 1 && *ExcIVI->idx_begin() == 0) {
+        ExnObj = ExcIVI->getOperand(1);
+        SelLoad = dyn_cast<LoadInst>(SelIVI->getOperand(1));
+        EraseIVIs = true;
+      }
+    }
+  }
+
+  if (!ExnObj)
+    ExnObj = ExtractValueInst::Create(RI->getOperand(0), 0, "exn.obj", RI);
+
+  RI->eraseFromParent();
+
+  if (EraseIVIs) {
+    if (SelIVI->use_empty())
+      SelIVI->eraseFromParent();
+    if (ExcIVI->use_empty())
+      ExcIVI->eraseFromParent();
+    if (SelLoad && SelLoad->use_empty())
+      SelLoad->eraseFromParent();
+  }
+
+  return ExnObj;
+}
+
+/// Replace resumes that are not reachable from a cleanup landing pad with
+/// unreachable and then simplify those blocks.
+size_t DwarfEHPrepare::pruneUnreachableResumes(
+    Function &Fn, SmallVectorImpl<ResumeInst *> &Resumes,
+    SmallVectorImpl<LandingPadInst *> &CleanupLPads) {
+  BitVector ResumeReachable(Resumes.size());
+  size_t ResumeIndex = 0;
+  for (auto *RI : Resumes) {
+    for (auto *LP : CleanupLPads) {
+      if (isPotentiallyReachable(LP, RI, nullptr, DT)) {
+        ResumeReachable.set(ResumeIndex);
+        break;
+      }
+    }
+    ++ResumeIndex;
+  }
+
+  // If everything is reachable, there is no change.
+  if (ResumeReachable.all())
+    return Resumes.size();
+
+  const TargetTransformInfo &TTI =
+      getAnalysis<TargetTransformInfoWrapperPass>().getTTI(Fn);
+  LLVMContext &Ctx = Fn.getContext();
+
+  // Otherwise, insert unreachable instructions and call simplifycfg.
+  size_t ResumesLeft = 0;
+  for (size_t I = 0, E = Resumes.size(); I < E; ++I) {
+    ResumeInst *RI = Resumes[I];
+    if (ResumeReachable[I]) {
+      Resumes[ResumesLeft++] = RI;
+    } else {
+      BasicBlock *BB = RI->getParent();
+      new UnreachableInst(Ctx, RI);
+      RI->eraseFromParent();
+      simplifyCFG(BB, TTI);
+    }
+  }
+  Resumes.resize(ResumesLeft);
+  return ResumesLeft;
+}
+
+/// InsertUnwindResumeCalls - Convert the ResumeInsts that are still present
+/// into calls to the appropriate _Unwind_Resume function.
+bool DwarfEHPrepare::InsertUnwindResumeCalls(Function &Fn) {
+  SmallVector<ResumeInst*, 16> Resumes;
+  SmallVector<LandingPadInst*, 16> CleanupLPads;
+  for (BasicBlock &BB : Fn) {
+    if (auto *RI = dyn_cast<ResumeInst>(BB.getTerminator()))
+      Resumes.push_back(RI);
+    if (auto *LP = BB.getLandingPadInst())
+      if (LP->isCleanup())
+        CleanupLPads.push_back(LP);
+  }
+
+  if (Resumes.empty())
+    return false;
+
+  // Check the personality, don't do anything if it's scope-based.
+  EHPersonality Pers = classifyEHPersonality(Fn.getPersonalityFn());
+  if (isScopedEHPersonality(Pers))
+    return false;
+
+  LLVMContext &Ctx = Fn.getContext();
+
+  size_t ResumesLeft = pruneUnreachableResumes(Fn, Resumes, CleanupLPads);
+  if (ResumesLeft == 0)
+    return true; // We pruned them all.
+
+  // Find the rewind function if we didn't already.
+  if (!RewindFunction) {
+    FunctionType *FTy = FunctionType::get(Type::getVoidTy(Ctx),
+                                          Type::getInt8PtrTy(Ctx), false);
+    const char *RewindName = TLI->getLibcallName(RTLIB::UNWIND_RESUME);
+    RewindFunction = Fn.getParent()->getOrInsertFunction(RewindName, FTy);
+  }
+
+  // Create the basic block where the _Unwind_Resume call will live.
+  if (ResumesLeft == 1) {
+    // Instead of creating a new BB and PHI node, just append the call to
+    // _Unwind_Resume to the end of the single resume block.
+    ResumeInst *RI = Resumes.front();
+    BasicBlock *UnwindBB = RI->getParent();
+    Value *ExnObj = GetExceptionObject(RI);
+
+    // Call the _Unwind_Resume function.
+    CallInst *CI = CallInst::Create(RewindFunction, ExnObj, "", UnwindBB);
+    CI->setCallingConv(TLI->getLibcallCallingConv(RTLIB::UNWIND_RESUME));
+
+    // We never expect _Unwind_Resume to return.
+    new UnreachableInst(Ctx, UnwindBB);
+    return true;
+  }
+
+  BasicBlock *UnwindBB = BasicBlock::Create(Ctx, "unwind_resume", &Fn);
+  PHINode *PN = PHINode::Create(Type::getInt8PtrTy(Ctx), ResumesLeft,
+                                "exn.obj", UnwindBB);
+
+  // Extract the exception object from the ResumeInst and add it to the PHI node
+  // that feeds the _Unwind_Resume call.
+  for (ResumeInst *RI : Resumes) {
+    BasicBlock *Parent = RI->getParent();
+    BranchInst::Create(UnwindBB, Parent);
+
+    Value *ExnObj = GetExceptionObject(RI);
+    PN->addIncoming(ExnObj, Parent);
+
+    ++NumResumesLowered;
+  }
+
+  // Call the function.
+  CallInst *CI = CallInst::Create(RewindFunction, PN, "", UnwindBB);
+  CI->setCallingConv(TLI->getLibcallCallingConv(RTLIB::UNWIND_RESUME));
+
+  // We never expect _Unwind_Resume to return.
+  new UnreachableInst(Ctx, UnwindBB);
+  return true;
+}
+
+bool DwarfEHPrepare::runOnFunction(Function &Fn) {
+  const TargetMachine &TM =
+      getAnalysis<TargetPassConfig>().getTM<TargetMachine>();
+  DT = &getAnalysis<DominatorTreeWrapperPass>().getDomTree();
+  TLI = TM.getSubtargetImpl(Fn)->getTargetLowering();
+  bool Changed = InsertUnwindResumeCalls(Fn);
+  DT = nullptr;
+  TLI = nullptr;
+  return Changed;
+}