Revert r229944: EH: Prune unreachable resume instructions during Dwarf EH preparation

This doesn't pass 'ninja check-llvm' for me. Lots of tests, including
the ones updated, fail with crashes and other explosions.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@229952 91177308-0d34-0410-b5e6-96231b3b80d8

lib/CodeGen/DwarfEHPrepare.cpp

@@ -13,18 +13,13 @@
 //===----------------------------------------------------------------------===//
 
 #include "llvm/CodeGen/Passes.h"
-#include "llvm/ADT/BitVector.h"
 #include "llvm/ADT/Statistic.h"
-#include "llvm/Analysis/CFG.h"
-#include "llvm/Analysis/TargetTransformInfo.h"
-#include "llvm/IR/Dominators.h"
 #include "llvm/IR/Function.h"
 #include "llvm/IR/Instructions.h"
 #include "llvm/IR/Module.h"
 #include "llvm/Pass.h"
 #include "llvm/Target/TargetLowering.h"
 #include "llvm/Target/TargetSubtargetInfo.h"
-#include "llvm/Transforms/Utils/Local.h"
 using namespace llvm;
 
 #define DEBUG_TYPE "dwarfehprepare"
@@ -38,28 +33,18 @@ namespace {
     // RewindFunction - _Unwind_Resume or the target equivalent.
     Constant *RewindFunction;
 
-    DominatorTree *DT;
-    const TargetLowering *TLI;
-
     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.
 
     // INITIALIZE_TM_PASS requires a default constructor, but it isn't used in
     // practice.
-    DwarfEHPrepare()
-        : FunctionPass(ID), TM(nullptr), RewindFunction(nullptr), DT(nullptr),
-          TLI(nullptr) {}
+    DwarfEHPrepare() : FunctionPass(ID), TM(nullptr), RewindFunction(nullptr) {}
 
     DwarfEHPrepare(const TargetMachine *TM)
-        : FunctionPass(ID), TM(TM), RewindFunction(nullptr), DT(nullptr),
-          TLI(nullptr) {}
+        : FunctionPass(ID), TM(TM), RewindFunction(nullptr) {}
 
     bool runOnFunction(Function &Fn) override;
 
@@ -68,8 +53,6 @@ namespace {
       return false;
     }
 
-    void getAnalysisUsage(AnalysisUsage &AU) const override;
-
     const char *getPassName() const override {
       return "Exception handling preparation";
     }
@@ -77,22 +60,13 @@ namespace {
 } // end anonymous namespace
 
 char DwarfEHPrepare::ID = 0;
-INITIALIZE_TM_PASS_BEGIN(DwarfEHPrepare, "dwarfehprepare",
-                         "Prepare DWARF exceptions", false, false)
-INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)
-INITIALIZE_PASS_DEPENDENCY(TargetTransformInfoWrapperPass)
-INITIALIZE_TM_PASS_END(DwarfEHPrepare, "dwarfehprepare",
-                       "Prepare DWARF exceptions", false, false)
+INITIALIZE_TM_PASS(DwarfEHPrepare, "dwarfehprepare", "Prepare DWARF exceptions",
+                   false, false)
 
 FunctionPass *llvm::createDwarfEHPass(const TargetMachine *TM) {
   return new DwarfEHPrepare(TM);
 }
 
-void DwarfEHPrepare::getAnalysisUsage(AnalysisUsage &AU) const {
-  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.
@@ -133,71 +107,21 @@ Value *DwarfEHPrepare::GetExceptionObject(ResumeInst *RI) {
   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, 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, 1, TLI->getDataLayout());
-    }
-  }
-  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;
 
-  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.
+  const TargetLowering *TLI = TM->getSubtargetImpl(Fn)->getTargetLowering();
+  LLVMContext &Ctx = Fn.getContext();
   if (!RewindFunction) {
     FunctionType *FTy = FunctionType::get(Type::getVoidTy(Ctx),
                                           Type::getInt8PtrTy(Ctx), false);
@@ -206,7 +130,9 @@ bool DwarfEHPrepare::InsertUnwindResumeCalls(Function &Fn) {
   }
 
   // Create the basic block where the _Unwind_Resume call will live.
-  if (ResumesLeft == 1) {
+  unsigned ResumesSize = Resumes.size();
+
+  if (ResumesSize == 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();
@@ -223,7 +149,7 @@ bool DwarfEHPrepare::InsertUnwindResumeCalls(Function &Fn) {
   }
 
   BasicBlock *UnwindBB = BasicBlock::Create(Ctx, "unwind_resume", &Fn);
-  PHINode *PN = PHINode::Create(Type::getInt8PtrTy(Ctx), ResumesLeft,
+  PHINode *PN = PHINode::Create(Type::getInt8PtrTy(Ctx), ResumesSize,
                                 "exn.obj", UnwindBB);
 
   // Extract the exception object from the ResumeInst and add it to the PHI node
@@ -249,10 +175,6 @@ bool DwarfEHPrepare::InsertUnwindResumeCalls(Function &Fn) {
 
 bool DwarfEHPrepare::runOnFunction(Function &Fn) {
   assert(TM && "DWARF EH preparation requires a target machine");
-  DT = &getAnalysis<DominatorTreeWrapperPass>().getDomTree();
-  TLI = TM->getSubtargetImpl(Fn)->getTargetLowering();
   bool Changed = InsertUnwindResumeCalls(Fn);
-  DT = nullptr;
-  TLI = nullptr;
   return Changed;
 }