Ejemplo n.º 1
0
bool TailCallElim::runTRE(Function &F) {
  // If this function is a varargs function, we won't be able to PHI the args
  // right, so don't even try to convert it...
  if (F.getFunctionType()->isVarArg()) return false;

  TTI = &getAnalysis<TargetTransformInfo>();
  BasicBlock *OldEntry = nullptr;
  bool TailCallsAreMarkedTail = false;
  SmallVector<PHINode*, 8> ArgumentPHIs;
  bool MadeChange = false;

  // CanTRETailMarkedCall - If false, we cannot perform TRE on tail calls
  // marked with the 'tail' attribute, because doing so would cause the stack
  // size to increase (real TRE would deallocate variable sized allocas, TRE
  // doesn't).
  bool CanTRETailMarkedCall = CanTRE(F);

  // Change any tail recursive calls to loops.
  //
  // FIXME: The code generator produces really bad code when an 'escaping
  // alloca' is changed from being a static alloca to being a dynamic alloca.
  // Until this is resolved, disable this transformation if that would ever
  // happen.  This bug is PR962.
  for (Function::iterator BB = F.begin(), E = F.end(); BB != E; ++BB) {
    if (ReturnInst *Ret = dyn_cast<ReturnInst>(BB->getTerminator())) {
      bool Change = ProcessReturningBlock(Ret, OldEntry, TailCallsAreMarkedTail,
                                          ArgumentPHIs, !CanTRETailMarkedCall);
      if (!Change && BB->getFirstNonPHIOrDbg() == Ret)
        Change = FoldReturnAndProcessPred(BB, Ret, OldEntry,
                                          TailCallsAreMarkedTail, ArgumentPHIs,
                                          !CanTRETailMarkedCall);
      MadeChange |= Change;
    }
  }

  // If we eliminated any tail recursions, it's possible that we inserted some
  // silly PHI nodes which just merge an initial value (the incoming operand)
  // with themselves.  Check to see if we did and clean up our mess if so.  This
  // occurs when a function passes an argument straight through to its tail
  // call.
  for (unsigned i = 0, e = ArgumentPHIs.size(); i != e; ++i) {
    PHINode *PN = ArgumentPHIs[i];

    // If the PHI Node is a dynamic constant, replace it with the value it is.
    if (Value *PNV = SimplifyInstruction(PN)) {
      PN->replaceAllUsesWith(PNV);
      PN->eraseFromParent();
    }
  }

  return MadeChange;
}
bool TailCallElim::runOnFunction(Function &F) {
  // If this function is a varargs function, we won't be able to PHI the args
  // right, so don't even try to convert it...
  if (F.getFunctionType()->isVarArg()) return false;

  TTI = &getAnalysis<TargetTransformInfo>();
  BasicBlock *OldEntry = 0;
  bool TailCallsAreMarkedTail = false;
  SmallVector<PHINode*, 8> ArgumentPHIs;
  bool MadeChange = false;

  // CanTRETailMarkedCall - If false, we cannot perform TRE on tail calls
  // marked with the 'tail' attribute, because doing so would cause the stack
  // size to increase (real TRE would deallocate variable sized allocas, TRE
  // doesn't).
  bool CanTRETailMarkedCall = true;

  // Find calls that can be marked tail.
  AllocaCaptureTracker ACT;
  for (Function::iterator BB = F.begin(), EE = F.end(); BB != EE; ++BB) {
    for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I) {
      if (AllocaInst *AI = dyn_cast<AllocaInst>(I)) {
        CanTRETailMarkedCall &= CanTRE(AI);
        PointerMayBeCaptured(AI, &ACT);
        // If any allocas are captured, exit.
        if (ACT.Captured)
          return false;
      }
    }
  }

  // Second pass, change any tail recursive calls to loops.
  //
  // FIXME: The code generator produces really bad code when an 'escaping
  // alloca' is changed from being a static alloca to being a dynamic alloca.
  // Until this is resolved, disable this transformation if that would ever
  // happen.  This bug is PR962.
  if (ACT.UsesAlloca.empty()) {
    for (Function::iterator BB = F.begin(), E = F.end(); BB != E; ++BB) {
      if (ReturnInst *Ret = dyn_cast<ReturnInst>(BB->getTerminator())) {
        bool Change = ProcessReturningBlock(Ret, OldEntry, TailCallsAreMarkedTail,
                                            ArgumentPHIs, !CanTRETailMarkedCall);
        if (!Change && BB->getFirstNonPHIOrDbg() == Ret)
          Change = FoldReturnAndProcessPred(BB, Ret, OldEntry,
                                            TailCallsAreMarkedTail, ArgumentPHIs,
                                            !CanTRETailMarkedCall);
        MadeChange |= Change;
      }
    }
  }

  // If we eliminated any tail recursions, it's possible that we inserted some
  // silly PHI nodes which just merge an initial value (the incoming operand)
  // with themselves.  Check to see if we did and clean up our mess if so.  This
  // occurs when a function passes an argument straight through to its tail
  // call.
  if (!ArgumentPHIs.empty()) {
    for (unsigned i = 0, e = ArgumentPHIs.size(); i != e; ++i) {
      PHINode *PN = ArgumentPHIs[i];

      // If the PHI Node is a dynamic constant, replace it with the value it is.
      if (Value *PNV = SimplifyInstruction(PN)) {
        PN->replaceAllUsesWith(PNV);
        PN->eraseFromParent();
      }
    }
  }

  // At this point, we know that the function does not have any captured
  // allocas. If additionally the function does not call setjmp, mark all calls
  // in the function that do not access stack memory with the tail keyword. This
  // implies ensuring that there does not exist any path from a call that takes
  // in an alloca but does not capture it and the call which we wish to mark
  // with "tail".
  if (!F.callsFunctionThatReturnsTwice()) {
    for (Function::iterator BB = F.begin(), E = F.end(); BB != E; ++BB) {
      for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I) {
        if (CallInst *CI = dyn_cast<CallInst>(I)) {
          if (!ACT.UsesAlloca.count(CI)) {
            CI->setTailCall();
            MadeChange = true;
          }
        }
      }
    }
  }

  return MadeChange;
}
bool TailCallElim::runOnFunction(Function &F) {
  // If this function is a varargs function, we won't be able to PHI the args
  // right, so don't even try to convert it...
  if (F.getFunctionType()->isVarArg()) return false;

  BasicBlock *OldEntry = 0;
  bool TailCallsAreMarkedTail = false;
  SmallVector<PHINode*, 8> ArgumentPHIs;
  bool MadeChange = false;
  bool FunctionContainsEscapingAllocas = false;

  // CannotTCETailMarkedCall - If true, we cannot perform TCE on tail calls
  // marked with the 'tail' attribute, because doing so would cause the stack
  // size to increase (real TCE would deallocate variable sized allocas, TCE
  // doesn't).
  bool CannotTCETailMarkedCall = false;

  // Loop over the function, looking for any returning blocks, and keeping track
  // of whether this function has any non-trivially used allocas.
  for (Function::iterator BB = F.begin(), E = F.end(); BB != E; ++BB) {
    if (FunctionContainsEscapingAllocas && CannotTCETailMarkedCall)
      break;

    FunctionContainsEscapingAllocas |=
      CheckForEscapingAllocas(BB, CannotTCETailMarkedCall);
  }
  
  /// FIXME: The code generator produces really bad code when an 'escaping
  /// alloca' is changed from being a static alloca to being a dynamic alloca.
  /// Until this is resolved, disable this transformation if that would ever
  /// happen.  This bug is PR962.
  if (FunctionContainsEscapingAllocas)
    return false;

  // Second pass, change any tail calls to loops.
  for (Function::iterator BB = F.begin(), E = F.end(); BB != E; ++BB) {
    if (ReturnInst *Ret = dyn_cast<ReturnInst>(BB->getTerminator())) {
      bool Change = ProcessReturningBlock(Ret, OldEntry, TailCallsAreMarkedTail,
                                          ArgumentPHIs,CannotTCETailMarkedCall);
      if (!Change && BB->getFirstNonPHIOrDbg() == Ret)
        Change = FoldReturnAndProcessPred(BB, Ret, OldEntry,
                                          TailCallsAreMarkedTail, ArgumentPHIs,
                                          CannotTCETailMarkedCall);
      MadeChange |= Change;
    }
  }

  // If we eliminated any tail recursions, it's possible that we inserted some
  // silly PHI nodes which just merge an initial value (the incoming operand)
  // with themselves.  Check to see if we did and clean up our mess if so.  This
  // occurs when a function passes an argument straight through to its tail
  // call.
  if (!ArgumentPHIs.empty()) {
    for (unsigned i = 0, e = ArgumentPHIs.size(); i != e; ++i) {
      PHINode *PN = ArgumentPHIs[i];

      // If the PHI Node is a dynamic constant, replace it with the value it is.
      if (Value *PNV = SimplifyInstruction(PN)) {
        PN->replaceAllUsesWith(PNV);
        PN->eraseFromParent();
      }
    }
  }

  // Finally, if this function contains no non-escaping allocas, or calls
  // setjmp, mark all calls in the function as eligible for tail calls
  //(there is no stack memory for them to access).
  if (!FunctionContainsEscapingAllocas && !F.callsFunctionThatReturnsTwice())
    for (Function::iterator BB = F.begin(), E = F.end(); BB != E; ++BB)
      for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I)
        if (CallInst *CI = dyn_cast<CallInst>(I)) {
          CI->setTailCall();
          MadeChange = true;
        }

  return MadeChange;
}
Ejemplo n.º 4
0
/// MoveExceptionValueCalls - Ensure that eh.exception is only ever called from
/// landing pads by replacing calls outside of landing pads with direct use of
/// a register holding the appropriate value; this requires adding calls inside
/// all landing pads to initialize the register.  Also, move eh.exception calls
/// inside landing pads to the start of the landing pad (optional, but may make
/// things simpler for later passes).
bool DwarfEHPrepare::MoveExceptionValueCalls() {
  // If the eh.exception intrinsic is not declared in the module then there is
  // nothing to do.  Speed up compilation by checking for this common case.
  if (!ExceptionValueIntrinsic &&
      !F->getParent()->getFunction(Intrinsic::getName(Intrinsic::eh_exception)))
    return false;

  bool Changed = false;

  // Move calls to eh.exception that are inside a landing pad to the start of
  // the landing pad.
  for (BBSet::const_iterator LI = LandingPads.begin(), LE = LandingPads.end();
       LI != LE; ++LI) {
    BasicBlock *LP = *LI;
    for (BasicBlock::iterator II = LP->getFirstNonPHIOrDbg(), IE = LP->end();
         II != IE;)
      if (EHExceptionInst *EI = dyn_cast<EHExceptionInst>(II++)) {
        // Found a call to eh.exception.
        if (!EI->use_empty()) {
          // If there is already a call to eh.exception at the start of the
          // landing pad, then get hold of it; otherwise create such a call.
          Value *CallAtStart = CreateExceptionValueCall(LP);

          // If the call was at the start of a landing pad then leave it alone.
          if (EI == CallAtStart)
            continue;
          EI->replaceAllUsesWith(CallAtStart);
        }
        EI->eraseFromParent();
        ++NumExceptionValuesMoved;
        Changed = true;
      }
  }

  // Look for calls to eh.exception that are not in a landing pad.  If one is
  // found, then a register that holds the exception value will be created in
  // each landing pad, and the SSAUpdater will be used to compute the values
  // returned by eh.exception calls outside of landing pads.
  SSAUpdater SSA;

  // Remember where we found the eh.exception call, to avoid rescanning earlier
  // basic blocks which we already know contain no eh.exception calls.
  bool FoundCallOutsideLandingPad = false;
  Function::iterator BB = F->begin();
  for (Function::iterator BE = F->end(); BB != BE; ++BB) {
    // Skip over landing pads.
    if (LandingPads.count(BB))
      continue;

    for (BasicBlock::iterator II = BB->getFirstNonPHIOrDbg(), IE = BB->end();
         II != IE; ++II)
      if (isa<EHExceptionInst>(II)) {
        SSA.Initialize(II->getType(), II->getName());
        FoundCallOutsideLandingPad = true;
        break;
      }

    if (FoundCallOutsideLandingPad)
      break;
  }

  // If all calls to eh.exception are in landing pads then we are done.
  if (!FoundCallOutsideLandingPad)
    return Changed;

  // Add a call to eh.exception at the start of each landing pad, and tell the
  // SSAUpdater that this is the value produced by the landing pad.
  for (BBSet::iterator LI = LandingPads.begin(), LE = LandingPads.end();
       LI != LE; ++LI)
    SSA.AddAvailableValue(*LI, CreateExceptionValueCall(*LI));

  // Now turn all calls to eh.exception that are not in a landing pad into a use
  // of the appropriate register.
  for (Function::iterator BE = F->end(); BB != BE; ++BB) {
    // Skip over landing pads.
    if (LandingPads.count(BB))
      continue;

    for (BasicBlock::iterator II = BB->getFirstNonPHIOrDbg(), IE = BB->end();
         II != IE;)
      if (EHExceptionInst *EI = dyn_cast<EHExceptionInst>(II++)) {
        // Found a call to eh.exception, replace it with the value from any
        // upstream landing pad(s).
        EI->replaceAllUsesWith(SSA.GetValueAtEndOfBlock(BB));
        EI->eraseFromParent();
        ++NumExceptionValuesMoved;
      }
  }

  return true;
}