path: root/lib/CodeGen/DwarfEHPrepare.cpp

//===-- DwarfEHPrepare - Prepare exception handling for code generation ---===//
//
//                     The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This pass mulches exception handling code into a form adapted to code
// generation. Required if using dwarf exception handling.
//
//===----------------------------------------------------------------------===//

#define DEBUG_TYPE "dwarfehprepare"
#include "llvm/Function.h"
#include "llvm/Instructions.h"
#include "llvm/IntrinsicInst.h"
#include "llvm/Module.h"
#include "llvm/Pass.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/Analysis/Dominators.h"
#include "llvm/CodeGen/Passes.h"
#include "llvm/MC/MCAsmInfo.h"
#include "llvm/Target/TargetLowering.h"
#include "llvm/Transforms/Utils/BasicBlockUtils.h"
#include "llvm/Transforms/Utils/PromoteMemToReg.h"
using namespace llvm;

STATISTIC(NumLandingPadsSplit,     "Number of landing pads split");
STATISTIC(NumUnwindsLowered,       "Number of unwind instructions lowered");
STATISTIC(NumExceptionValuesMoved, "Number of eh.exception calls moved");
STATISTIC(NumStackTempsIntroduced, "Number of stack temporaries introduced");

namespace {
  class DwarfEHPrepare : public FunctionPass {
    const TargetLowering *TLI;
    bool CompileFast;

    // The eh.exception intrinsic.
    Function *ExceptionValueIntrinsic;

    // The eh.selector intrinsic.
    Function *SelectorIntrinsic;

    // _Unwind_Resume_or_Rethrow call.
    Constant *URoR;

    // The EH language-specific catch-all type.
    GlobalVariable *EHCatchAllValue;

    // _Unwind_Resume or the target equivalent.
    Constant *RewindFunction;

    // Dominator info is used when turning stack temporaries into registers.
    DominatorTree *DT;
    DominanceFrontier *DF;

    // The function we are running on.
    Function *F;

    // The landing pads for this function.
    typedef SmallPtrSet<BasicBlock*, 8> BBSet;
    BBSet LandingPads;

    // Stack temporary used to hold eh.exception values.
    AllocaInst *ExceptionValueVar;

    bool NormalizeLandingPads();
    bool LowerUnwinds();
    bool MoveExceptionValueCalls();
    bool FinishStackTemporaries();
    bool PromoteStackTemporaries();

    Instruction *CreateExceptionValueCall(BasicBlock *BB);
    Instruction *CreateValueLoad(BasicBlock *BB);

    /// CreateReadOfExceptionValue - Return the result of the eh.exception
    /// intrinsic by calling the intrinsic if in a landing pad, or loading it
    /// from the exception value variable otherwise.
    Instruction *CreateReadOfExceptionValue(BasicBlock *BB) {
      return LandingPads.count(BB) ?
        CreateExceptionValueCall(BB) : CreateValueLoad(BB);
    }

    /// CleanupSelectors - Any remaining eh.selector intrinsic calls which still
    /// use the ".llvm.eh.catch.all.value" call need to convert to using its
    /// initializer instead.
    bool CleanupSelectors();

    /// FindAllCleanupSelectors - Find all eh.selector calls that are clean-ups.
    void FindAllCleanupSelectors(SmallPtrSet<IntrinsicInst*, 32> &Sels);

    /// FindAllURoRInvokes - Find all URoR invokes in the function.
    void FindAllURoRInvokes(SmallPtrSet<InvokeInst*, 32> &URoRInvokes);

    /// HandleURoRInvokes - Handle invokes of "_Unwind_Resume_or_Rethrow"
    /// calls. The "unwind" part of these invokes jump to a landing pad within
    /// the current function. This is a candidate to merge the selector
    /// associated with the URoR invoke with the one from the URoR's landing
    /// pad.
    bool HandleURoRInvokes();

    /// FindSelectorAndURoR - Find the eh.selector call and URoR call associated
    /// with the eh.exception call. This recursively looks past instructions
    /// which don't change the EH pointer value, like casts or PHI nodes.
    bool FindSelectorAndURoR(Instruction *Inst, bool &URoRInvoke,
                             SmallPtrSet<IntrinsicInst*, 8> &SelCalls);
      
    /// DoMem2RegPromotion - Take an alloca call and promote it from memory to a
    /// register.
    bool DoMem2RegPromotion(Value *V) {
      AllocaInst *AI = dyn_cast<AllocaInst>(V);
      if (!AI || !isAllocaPromotable(AI)) return false;

      // Turn the alloca into a register.
      std::vector<AllocaInst*> Allocas(1, AI);
      PromoteMemToReg(Allocas, *DT, *DF);
      return true;
    }

    /// PromoteStoreInst - Perform Mem2Reg on a StoreInst.
    bool PromoteStoreInst(StoreInst *SI) {
      if (!SI || !DT || !DF) return false;
      if (DoMem2RegPromotion(SI->getOperand(1)))
        return true;
      return false;
    }

    /// PromoteEHPtrStore - Promote the storing of an EH pointer into a
    /// register. This should get rid of the store and subsequent loads.
    bool PromoteEHPtrStore(IntrinsicInst *II) {
      if (!DT || !DF) return false;

      bool Changed = false;
      StoreInst *SI;

      while (1) {
        SI = 0;
        for (Value::use_iterator
               I = II->use_begin(), E = II->use_end(); I != E; ++I) {
          SI = dyn_cast<StoreInst>(I);
          if (SI) break;
        }

        if (!PromoteStoreInst(SI))
          break;

        Changed = true;
      }

      return false;
    }

  public:
    static char ID; // Pass identification, replacement for typeid.
    DwarfEHPrepare(const TargetLowering *tli, bool fast) :
      FunctionPass(&ID), TLI(tli), CompileFast(fast),
      ExceptionValueIntrinsic(0), SelectorIntrinsic(0),
      URoR(0), EHCatchAllValue(0), RewindFunction(0) {}

    virtual bool runOnFunction(Function &Fn);

    // getAnalysisUsage - We need dominance frontiers for memory promotion.
    virtual void getAnalysisUsage(AnalysisUsage &AU) const {
      if (!CompileFast)
        AU.addRequired<DominatorTree>();
      AU.addPreserved<DominatorTree>();
      if (!CompileFast)
        AU.addRequired<DominanceFrontier>();
      AU.addPreserved<DominanceFrontier>();
    }

    const char *getPassName() const {
      return "Exception handling preparation";
    }

  };
} // end anonymous namespace

char DwarfEHPrepare::ID = 0;

FunctionPass *llvm::createDwarfEHPass(const TargetLowering *tli, bool fast) {
  return new DwarfEHPrepare(tli, fast);
}

/// FindAllCleanupSelectors - Find all eh.selector calls that are clean-ups.
void DwarfEHPrepare::
FindAllCleanupSelectors(SmallPtrSet<IntrinsicInst*, 32> &Sels) {
  for (Value::use_iterator
         I = SelectorIntrinsic->use_begin(),
         E = SelectorIntrinsic->use_end(); I != E; ++I) {
    IntrinsicInst *SI = cast<IntrinsicInst>(I);
    if (!SI || SI->getParent()->getParent() != F) continue;

    unsigned NumOps