path: root/lib/Analysis/ScalarEvolutionExpander.cpp

//===- ScalarEvolutionExpander.cpp - Scalar Evolution Analysis --*- C++ -*-===//
//
//                     The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file contains the implementation of the scalar evolution expander,
// which is used to generate the code corresponding to a given scalar evolution
// expression.
//
//===----------------------------------------------------------------------===//

#include "llvm/Analysis/ScalarEvolutionExpander.h"
#include "llvm/Analysis/LoopInfo.h"
using namespace llvm;

/// InsertCastOfTo - Insert a cast of V to the specified type, doing what
/// we can to share the casts.
Value *SCEVExpander::InsertCastOfTo(Instruction::CastOps opcode, Value *V, 
                                    const Type *Ty) {
  // Short-circuit unnecessary bitcasts.
  if (opcode == Instruction::BitCast && V->getType() == Ty)
    return V;

  // Short-circuit unnecessary inttoptr<->ptrtoint casts.
  if ((opcode == Instruction::PtrToInt || opcode == Instruction::IntToPtr) &&
      SE.getTypeSizeInBits(Ty) == SE.getTypeSizeInBits(V->getType()))
    if (CastInst *CI = dyn_cast<CastInst>(V))
      if ((CI->getOpcode() == Instruction::PtrToInt ||
           CI->getOpcode() == Instruction::IntToPtr) &&
          SE.getTypeSizeInBits(CI->getType()) ==
          SE.getTypeSizeInBits(CI->getOperand(0)->getType()))
        return CI->getOperand(0);

  // FIXME: keep track of the cast instruction.
  if (Constant *C = dyn_cast<Constant>(V))
    return ConstantExpr::getCast(opcode, C, Ty);
  
  if (Argument *A = dyn_cast<Argument>(V)) {
    // Check to see if there is already a cast!
    for (Value::use_iterator UI = A->use_begin(), E = A->use_end();
         UI != E; ++UI) {
      if ((*UI)->getType() == Ty)
        if (CastInst *CI = dyn_cast<CastInst>(cast<Instruction>(*UI)))
          if (CI->getOpcode() == opcode) {
            // If the cast isn't the first instruction of the function, move it.
            if (BasicBlock::iterator(CI) != 
                A->getParent()->getEntryBlock().begin()) {
              // If the CastInst is the insert point, change the insert point.
              if (CI == InsertPt) ++InsertPt;
              // Splice the cast at the beginning of the entry block.
              CI->moveBefore(A->getParent()->getEntryBlock().begin());
            }
            return CI;
          }
    }
    return CastInst::Create(opcode, V, Ty, V->getName(), 
                            A->getParent()->getEntryBlock().begin());
  }

  Instruction *I = cast<Instruction>(V);

  // Check to see if there is already a cast.  If there is, use it.
  for (Value::use_iterator UI = I->use_begin(), E = I->use_end();
       UI != E; ++UI) {
    if ((*UI)->getType() == Ty)
      if (CastInst *CI = dyn_cast<CastInst>(cast<Instruction>(*UI)))
        if (CI->getOpcode() == opcode) {
          BasicBlock::iterator It = I; ++It;
          if (isa<InvokeInst>(I))
            It = cast<InvokeInst>(I)->getNormalDest()->begin();
          while (isa<PHINode>(It)) ++It;
          if (It != BasicBlock::iterator(CI)) {
            // If the CastInst is the insert point, change the insert point.
            if (CI == InsertPt) ++InsertPt;
            // Splice the cast immediately after the operand in question.
            CI->moveBefore(It);
          }
          return CI;
        }
  }
  BasicBlock::iterator IP = I; ++IP;
  if (InvokeInst *II = dyn_cast<InvokeInst>(I))
    IP = II->getNormalDest()->begin();
  while (isa<PHINode>(IP)) ++IP;
  return CastInst::Create(opcode, V, Ty, V->getName(), IP);
}

/// InsertNoopCastOfTo - Insert a cast of V to the specified type,
/// which must be possible with a noop cast.
Value *SCEVExpander::InsertNoopCastOfTo(Value *V, const Type *Ty) {
  Instruction::CastOps Op = CastInst::getCastOpcode(V, false, Ty, false);
  assert((Op == Instruction::BitCast ||
          Op == Instruction::PtrToInt ||
          Op == Instruction::IntToPtr) &&
         "InsertNoopCastOfTo cannot perform non-noop casts!");
  assert(SE.getTypeSizeInBits(V->getType()) == SE.getTypeSizeInBits(Ty) &&
         "InsertNoopCastOfTo cannot change sizes!");
  return InsertCastOfTo(Op, V, Ty);
}

/// InsertBinop - Insert the specified binary operator, doing a small amount
/// of work to avoid inserting an obviously redundant operation.
Value *SCEVExpander::InsertBinop(Instruction::BinaryOps Opcode, Value *LHS,
                                 Value *RHS, BasicBlock::iterator InsertPt) {
  // Fold a binop with constant operands.
  if (Constant *CLHS = dyn_cast<Constant>(LHS))
    if (Constant *CRHS = dyn_cast<Constant>(RHS))
      return ConstantExpr::get(Opcode, CLHS, CRHS);

  // Do a quick scan to see if we have this binop nearby.  If so, reuse it.
  unsigned ScanLimit = 6;
  BasicBlock::iterator BlockBegin = InsertPt->getParent()->begin();
  if (InsertPt != BlockBegin) {
    // Scanning starts from the last instruction before InsertPt.
    BasicBlock::iterator IP = InsertPt;
    --IP;
    for (; ScanLimit; --IP, --ScanLimit) {
      if (BinaryOperator *BinOp = dyn_cast<BinaryOperator>(IP))
        if (BinOp->getOpcode() == Opcode && BinOp->getOperand(0) == LHS &&
            BinOp->getOperand(1) == RHS)
          return BinOp;
      if (IP == BlockBegin) break;
    }
  }
  
  // If we haven't found this binop, insert it.
  return BinaryOperator::Create(Opcode, LHS, RHS, "tmp", InsertPt);
}

Value *SCEVExpander::visitAddExpr(const SCEVAddExpr *S) {
  const Type *Ty = SE.getEffectiveSCEVType(S->getType());
  Value *V = expand(S->getOperand(S->getNumOperands()-1));
  V = InsertNoopCastOfTo(V, Ty);

  // Emit a bunch of add instructions
  for (int i = S->getNumOperands()-2; i >= 0; --i) {
    Value *W = expand(S->getOperand(i));
    W = InsertNoopCastOfTo(W, Ty);
    V = InsertBinop(Instruction::Add, V, W, InsertPt);
  }
  return V;
}
    
Value *SCEVExpander::visitMulExpr(const SCEVMulExpr *S) {
  const Type *Ty = SE.getEffectiveSCEVType(S->getType());
  int FirstOp = 0;  // Set if we should emit a subtract.
  if (const SCEVConstant *SC = dyn_cast<SCEVConstant>(S->getOperand(0)))
    if (SC->getValue()->isAllOnesValue())
      FirstOp = 1;

  int i = S->getNumOperands()-2;
  Value *V = expand(S->getOperand(i+1));
  V = InsertNoopCastOfTo(V, Ty);

  // Emit a bunch of multiply instructions
  for (; i >= FirstOp; --i) {
    Value *W = expand(S->getOperand(i));
    W = InsertNoopCastOfTo(W, Ty);
    V = InsertBinop(Instruction::Mul, V, W, InsertPt);
  }

  // -1 * ...  --->  0 - ...
  if (FirstOp == 1)
    V = InsertBinop(Instruction::Sub, Constant::getNullValue(Ty), V, InsertPt);
  return V;
}

Value *SCEVExpander::visitUDivExpr(const SCEVUDivExpr *S) {
  const Type *Ty = SE.getEffectiveSCEVType(S->getType());

  Value *LHS = expand(S->getLHS());
  LHS = InsertNoopCastOfTo(LHS, Ty);
  if (const SCEVConstant *SC = dyn_cast<SCEVConstant>(S->getRHS())) {
    const APInt