lib/Analysis/PHITransAddr.cpp

//===- PHITransAddr.cpp - PHI Translation for Addresses -------------------===//
//
//                     The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file implements the PHITransAddr class.
//
//===----------------------------------------------------------------------===//

#include "llvm/Analysis/PHITransAddr.h"
#include "llvm/Analysis/Dominators.h"
#include "llvm/Analysis/InstructionSimplify.h"
using namespace llvm;

/// IsPotentiallyPHITranslatable - If this needs PHI translation, return true
/// if we have some hope of doing it.  This should be used as a filter to
/// avoid calling PHITranslateValue in hopeless situations.
bool PHITransAddr::IsPotentiallyPHITranslatable() const {
  // If the input value is not an instruction, or if it is not defined in CurBB,
  // then we don't need to phi translate it.
  Instruction *Inst = dyn_cast<Instruction>(Addr);
  if (isa<PHINode>(Inst) ||
      isa<BitCastInst>(Inst) ||
      isa<GetElementPtrInst>(Inst) ||
      (Inst->getOpcode() == Instruction::And &&
       isa<ConstantInt>(Inst->getOperand(1))))
    return true;

  //   cerr << "MEMDEP: Could not PHI translate: " << *Pointer;
  //   if (isa<BitCastInst>(PtrInst) || isa<GetElementPtrInst>(PtrInst))
  //     cerr << "OP:\t\t\t\t" << *PtrInst->getOperand(0);

  return false;
}


Value *PHITransAddr::PHITranslateSubExpr(Value *V, BasicBlock *CurBB,
                                         BasicBlock *PredBB) {
  // If this is a non-instruction value, it can't require PHI translation.
  Instruction *Inst = dyn_cast<Instruction>(V);
  if (Inst == 0) return V;
  
  // Determine whether 'Inst' is an input to our PHI translatable expression.
  bool isInput = std::count(InstInputs.begin(), InstInputs.end(), Inst);
  
  // If 'Inst' is not defined in this block, it is either an input, or an
  // intermediate result.
  if (Inst->getParent() != CurBB) {
    // If it is an input, then it remains an input.
    if (isInput)
      return Inst;
  
    // Otherwise, it must be an intermediate result.  See if its operands need
    // to be phi translated, and if so, reconstruct it.
    
    if (BitCastInst *BC = dyn_cast<BitCastInst>(Inst)) {
      Value *PHIIn = PHITranslateSubExpr(BC->getOperand(0), CurBB, PredBB);
      if (PHIIn == 0) return 0;
      if (PHIIn == BC->getOperand(0))
        return BC;
      
      // Find an available version of this cast.
      
      // Constants are trivial to find.
      if (Constant *C = dyn_cast<Constant>(PHIIn))
        return ConstantExpr::getBitCast(C, BC->getType());
      
      // Otherwise we have to see if a bitcasted version of the incoming pointer
      // is available.  If so, we can use it, otherwise we have to fail.
      for (Value::use_iterator UI = PHIIn->use_begin(), E = PHIIn->use_end();
           UI != E; ++UI) {
        if (BitCastInst *BCI = dyn_cast<BitCastInst>(*UI))
          if (BCI->getType() == BC->getType())
            return BCI;
      }
      return 0;
    }
    
    // Handle getelementptr with at least one PHI translatable operand.
    if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(Inst)) {
      SmallVector<Value*, 8> GEPOps;
      BasicBlock *CurBB = GEP->getParent();
      bool AnyChanged = false;
      for (unsigned i = 0, e = GEP->getNumOperands(); i != e; ++i) {
        Value *GEPOp = PHITranslateSubExpr(GEP->getOperand(i), CurBB, PredBB);
        if (GEPOp == 0) return 0;
        
        AnyChanged = GEPOp != GEP->getOperand(i);
        GEPOps.push_back(GEPOp);
      }
      
      if (!AnyChanged)
        return GEP;
      
      // Simplify the GEP to handle 'gep x, 0' -> x etc.
      if (Value *V = SimplifyGEPInst(&GEPOps[0], GEPOps.size(), TD))
        return V;
      
      // Scan to see if we have this GEP available.
      Value *APHIOp = GEPOps[0];
      for (Value::use_iterator UI = APHIOp->use_begin(), E = APHIOp->use_end();
           UI != E; ++UI) {
        if (GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(*UI))
          if (GEPI->getType() == GEP->getType() &&
              GEPI->getNumOperands() == GEPOps.size() &&
              GEPI->getParent()->getParent() == CurBB->getParent()) {
            bool Mismatch = false;
            for (unsigned i = 0, e = GEPOps.size(); i != e; ++i)
              if (GEPI->getOperand(i) != GEPOps[i]) {
                Mismatch = true;
                break;
              }
            if (!Mismatch)
              return GEPI;
          }
      }
      return 0;
    }
    
    // Handle add with a constant RHS.
    if (Inst->getOpcode() == Instruction::Add &&
        isa<ConstantInt>(Inst->getOperand(1))) {
      // PHI translate the LHS.
      Constant *RHS = cast<ConstantInt>(Inst->getOperand(1));
      bool isNSW = cast<BinaryOperator>(Inst)->hasNoSignedWrap();
      bool isNUW = cast<BinaryOperator>(Inst)->hasNoUnsignedWrap();
      
      Value *LHS = PHITranslateSubExpr(Inst->getOperand(0), CurBB, PredBB);
      if (LHS == 0) return 0;
      
      // If the PHI translated LHS is an add of a constant, fold the immediates.
      if (BinaryOperator *BOp = dyn_cast<BinaryOperator>(LHS))
        if (BOp->getOpcode() == Instruction::Add)
          if (ConstantInt *CI = dyn_cast<ConstantInt>(BOp->getOperand(1))) {
            LHS = BOp->getOperand(0);
            RHS = ConstantExpr::getAdd(RHS, CI);
            isNSW = isNUW = false;
          }
      
      // See if the add simplifies away.
      if (Value *Res = SimplifyAddInst(LHS, RHS, isNSW, isNUW, TD))
        return Res;
      
      // Otherwise, see if we have this add available somewhere.
      for (Value::use_iterator UI = LHS->use_begin(), E = LHS->use_end();
           UI != E; ++UI) {
        if (BinaryOperator *BO = dyn_cast<BinaryOperator>(*UI))
          if (BO->getOperand(0) == LHS && BO->getOperand(1) == RHS &&
              BO->getParent()->getParent() == CurBB->getParent())
            return BO;
      }
      
      return 0;
    }
    
    // Otherwise, we failed.
    return 0;
  }

  // Otherwise, it is defined in this block.  It must be an input and must be
  // phi translated.
  assert(isInput && "Instruction defined in block must be an input");
  
  
  abort(); // unimplemented so far.
}


/// PHITranslateValue - PHI translate the current address up the CFG from
/// CurBB to Pred, updating our state the reflect any needed changes.  This
/// returns true on failure.
bool PHITransAddr::PHITranslateValue(BasicBlock *CurBB, BasicBlock *PredBB) {
  Addr = PHITranslateSubExpr(Addr, CurBB, PredBB);
  return Addr == 0;
}

/// GetAvailablePHITranslatedSubExpr - Return the value computed by
/// PHITranslateSubExpr if it dominates PredBB, otherwise return null.
Value *PHITransAddr::
GetAvailablePHITranslatedSubExpr(Value *V, BasicBlock *CurBB,BasicBlock *PredBB,
                                 const DominatorTree &DT) {
  // See if PHI translation succeeds.
  V = PHITranslateSubExpr(V, CurBB, PredBB);
  
  // Make sure the value is live in the predecessor.
  if (Instruction *Inst = dyn_cast_or_null<Instruction>(V))
    if (!DT.dominates(Inst->getParent(), PredBB))
      return 0;
  return V;
}


/// PHITranslateWithInsertion - PHI translate this value into the specified
/// predecessor block, inserting a computation of the value if it is
/// unavailable.
///
/// All newly created instructions are added to the NewInsts list.  This
/// returns null on failure.
///
Value *PHITransAddr::
PHITranslateWithInsertion(BasicBlock *CurBB, BasicBlock *PredBB,
                          const DominatorTree &DT,
                          SmallVectorImpl<Instruction*> &NewInsts) {
  unsigned NISize = NewInsts.size();
  
  // Attempt to PHI translate with insertion.
  Addr = InsertPHITranslatedSubExpr(Addr, CurBB, PredBB, DT, NewInsts);
  
  // If successful, return the new value.
  if (Addr) return Addr;
  
  // If not, destroy any intermediate instructions inserted.
  while (NewInsts.size() != NISize)
    NewInsts.pop_back_val()->eraseFromParent();
  return 0;
}


/// InsertPHITranslatedPointer - Insert a computation of the PHI translated
/// version of 'V' for the edge PredBB->CurBB into the end of the PredBB
/// block.  All newly created instructions are added to the NewInsts list.
/// This returns null on failure.
///
Value *PHITransAddr::
InsertPHITranslatedSubExpr(Value *InVal, BasicBlock *CurBB,
                           BasicBlock *PredBB, const DominatorTree &DT,
                           SmallVectorImpl<Instruction*> &NewInsts) {
  // See if we have a version of this value already available and dominating
  // PredBB.  If so, there is no need to insert a new instance of it.
  if (Value *Res = GetAvailablePHITranslatedSubExpr(InVal, CurBB, PredBB, DT))
    return Res;

  // If we don't have an available version of this value, it must be an
  // instruction.
  Instruction *Inst = cast<Instruction>(InVal);
  
  // Handle bitcast of PHI translatable value.
  if (BitCastInst *BC = dyn_cast<BitCastInst>(Inst)) {
    Value *OpVal = InsertPHITranslatedSubExpr(BC->getOperand(0),
                                              CurBB, PredBB, DT, NewInsts);
    if (OpVal == 0) return 0;
    
    // Otherwise insert a bitcast at the end of PredBB.
    BitCastInst *New = new BitCastInst(OpVal, InVal->getType(),
                                       InVal->getName()+".phi.trans.insert",
                                       PredBB->getTerminator());
    NewInsts.push_back(New);
    return New;
  }
  
  // Handle getelementptr with at least one PHI operand.
  if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(Inst)) {
    SmallVector<Value*, 8> GEPOps;
    BasicBlock *CurBB = GEP->getParent();
    for (unsigned i = 0, e = GEP->getNumOperands(); i != e; ++i) {
      Value *OpVal = InsertPHITranslatedSubExpr(GEP->getOperand(i),
                                                CurBB, PredBB, DT, NewInsts);
      if (OpVal == 0) return 0;
      GEPOps.push_back(OpVal);
    }
    
    GetElementPtrInst *Result = 
    GetElementPtrInst::Create(GEPOps[0], GEPOps.begin()+1, GEPOps.end(),
                              InVal->getName()+".phi.trans.insert",
                              PredBB->getTerminator());
    Result->setIsInBounds(GEP->isInBounds());
    NewInsts.push_back(Result);
    return Result;
  }
  
#if 0
  // FIXME: This code works, but it is unclear that we actually want to insert
  // a big chain of computation in order to make a value available in a block.
  // This needs to be evaluated carefully to consider its cost trade offs.
  
  // Handle add with a constant RHS.
  if (Inst->getOpcode() == Instruction::Add &&
      isa<ConstantInt>(Inst->getOperand(1))) {
    // PHI translate the LHS.
    Value *OpVal = InsertPHITranslatedSubExpr(Inst->getOperand(0),
                                              CurBB, PredBB, DT, NewInsts);
    if (OpVal == 0) return 0;
    
    BinaryOperator *Res = BinaryOperator::CreateAdd(OpVal, Inst->getOperand(1),
                                           InVal->getName()+".phi.trans.insert",
                                                    PredBB->getTerminator());
    Res->setHasNoSignedWrap(cast<BinaryOperator>(Inst)->hasNoSignedWrap());
    Res->setHasNoUnsignedWrap(cast<BinaryOperator>(Inst)->hasNoUnsignedWrap());
    NewInsts.push_back(Res);
    return Res;
  }
#endif
  
  return 0;
}