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simplify CanEvaluateSExtd to return a bool now that we have a

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simpler profitability predicate.

llvm-svn: 93111
This commit is contained in:
Chris Lattner 2010-01-10 07:57:20 +00:00
parent fa864affbc
commit 67e0ef4d5d
1 changed files with 22 additions and 63 deletions
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85
lib/Transforms/InstCombine/InstCombineCasts.cpp
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@ -775,61 +775,36 @@ Instruction *InstCombiner::visitZExt(ZExtInst &CI) {
/// to promote integer operations to a wider types will allow us to eliminate
/// the extension.
///
/// This returns 0 if we can't do this or the number of sign bits that would be
/// set if we can. For example, CanEvaluateSExtd(i16 1, i64) would return 63,
/// because the computation can be extended (to "i64 1") and the resulting
/// computation has 63 equal sign bits.
/// This function works on both vectors and scalars.
///
/// This function works on both vectors and scalars. For vectors, the result is
/// the number of bits known sign extended in each element.
///
static unsigned CanEvaluateSExtd(Value *V, const Type *Ty, TargetData *TD) {
static bool CanEvaluateSExtd(Value *V, const Type *Ty, TargetData *TD) {
assert(V->getType()->getScalarSizeInBits() < Ty->getScalarSizeInBits() &&
"Can't sign extend type to a smaller type");
// If this is a constant, return the number of sign bits the extended version
// of it would have.
if (Constant *C = dyn_cast<Constant>(V))
return ComputeNumSignBits(ConstantExpr::getSExt(C, Ty), TD);
// If this is a constant, it can be trivially promoted.
if (isa<Constant>(V))
return true;
Instruction *I = dyn_cast<Instruction>(V);
if (!I) return 0;
if (!I) return false;
// If this is a truncate from the dest type, we can trivially eliminate it.
if (isa<TruncInst>(I) && I->getOperand(0)->getType() == Ty)
return ComputeNumSignBits(I->getOperand(0), TD);
return true;
// We can't extend or shrink something that has multiple uses: doing so would
// require duplicating the instruction in general, which isn't profitable.
if (!I->hasOneUse()) return 0;
if (!I->hasOneUse()) return false;
const Type *OrigTy = V->getType();
unsigned Opc = I->getOpcode();
unsigned Tmp1, Tmp2;
switch (Opc) {
switch (I->getOpcode()) {
case Instruction::And:
case Instruction::Or:
case Instruction::Xor:
// These operators can all arbitrarily be extended or truncated.
Tmp1 = CanEvaluateSExtd(I->getOperand(0), Ty, TD);
if (Tmp1 == 0) return 0;
Tmp2 = CanEvaluateSExtd(I->getOperand(1), Ty, TD);
return std::min(Tmp1, Tmp2);
case Instruction::Add:
case Instruction::Sub:
// Add/Sub can have at most one carry/borrow bit.
Tmp1 = CanEvaluateSExtd(I->getOperand(0), Ty, TD);
if (Tmp1 == 0) return 0;
Tmp2 = CanEvaluateSExtd(I->getOperand(1), Ty, TD);
if (Tmp2 == 0) return 0;
return std::min(Tmp1, Tmp2)-1;
case Instruction::Mul:
// These operators can all arbitrarily be extended or truncated.
if (!CanEvaluateSExtd(I->getOperand(0), Ty, TD))
return 0;
if (!CanEvaluateSExtd(I->getOperand(1), Ty, TD))
return 0;
return 1; // IMPROVE?
// These operators can all arbitrarily be extended if their inputs can.
return CanEvaluateSExtd(I->getOperand(0), Ty, TD) &&
CanEvaluateSExtd(I->getOperand(1), Ty, TD);
//case Instruction::Shl: TODO
//case Instruction::LShr: TODO
@ -839,39 +814,27 @@ static unsigned CanEvaluateSExtd(Value *V, const Type *Ty, TargetData *TD) {
case Instruction::ZExt: {
// sext(sext(x)) -> sext(x)
// sext(zext(x)) -> zext(x)
// Note that replacing a cast does not reduce the number of casts in the
// input.
unsigned InSignBits = ComputeNumSignBits(I, TD);
unsigned ExtBits = Ty->getScalarSizeInBits()-OrigTy->getScalarSizeInBits();
// We'll end up extending it all the way out.
return InSignBits+ExtBits;
}
case Instruction::Select: {
SelectInst *SI = cast<SelectInst>(I);
Tmp1 = CanEvaluateSExtd(SI->getTrueValue(), Ty, TD);
if (Tmp1 == 0) return 0;
Tmp2 = CanEvaluateSExtd(SI->getFalseValue(), Ty, TD);
return std::min(Tmp1, Tmp2);
return true;
}
case Instruction::Select:
return CanEvaluateSExtd(I->getOperand(1), Ty, TD) &&
CanEvaluateSExtd(I->getOperand(2), Ty, TD);
case Instruction::PHI: {
// We can change a phi if we can change all operands. Note that we never
// get into trouble with cyclic PHIs here because we only consider
// instructions with a single use.
PHINode *PN = cast<PHINode>(I);
unsigned Result = ~0U;
for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
Result = std::min(Result,
CanEvaluateSExtd(PN->getIncomingValue(i), Ty, TD));
if (Result == 0) return 0;
if (!CanEvaluateSExtd(PN->getIncomingValue(i), Ty, TD)) return false;
}
return Result;
return true;
}
default:
// TODO: Can handle more cases here.
break;
}
return 0;
return false;
}
Instruction *InstCombiner::visitSExt(SExtInst &CI) {
@ -901,11 +864,8 @@ Instruction *InstCombiner::visitSExt(SExtInst &CI) {
// type. Only do this if the dest type is a simple type, don't convert the
// expression tree to something weird like i93 unless the source is also
// strange.
if (isa<VectorType>(DestTy) || ShouldChangeType(SrcTy, DestTy)) {
unsigned NumBitsSExt = CanEvaluateSExtd(Src, DestTy, TD);
if (NumBitsSExt == 0)
return 0;
if ((isa<VectorType>(DestTy) || ShouldChangeType(SrcTy, DestTy)) &&
CanEvaluateSExtd(Src, DestTy, TD)) {
// Okay, we can transform this! Insert the new expression now.
DEBUG(dbgs() << "ICE: EvaluateInDifferentType converting expression type"
" to avoid sign extend: " << CI);
@ -917,8 +877,7 @@ Instruction *InstCombiner::visitSExt(SExtInst &CI) {
// If the high bits are already filled with sign bit, just replace this
// cast with the result.
if (NumBitsSExt > DestBitSize - SrcBitSize ||
ComputeNumSignBits(Res) > DestBitSize - SrcBitSize)
if (ComputeNumSignBits(Res) > DestBitSize - SrcBitSize)
return ReplaceInstUsesWith(CI, Res);
// We need to emit a shl + ashr to do the sign extend.