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rename CanEvaluateInDifferentType -> CanEvaluateTruncated and

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simplify it now that it is only used for truncates.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@93021 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Chris Lattner 2010-01-08 19:19:23 +00:00
parent ad5b52fd5e
commit 14bf8f0285
1 changed files with 28 additions and 71 deletions
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99
lib/Transforms/InstCombine/InstCombineCasts.cpp
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@ -147,29 +147,16 @@ Instruction *InstCombiner::PromoteCastOfAllocation(BitCastInst &CI,
}
/// CanEvaluateInDifferentType - Return true if we can take the specified value
/// and return it as type Ty without inserting any new casts and without
/// changing the computed value. This is used by code that tries to decide
/// whether promoting or shrinking integer operations to wider or smaller types
/// will allow us to eliminate a truncate or extend.
/// CanEvaluateTruncated - Return true if we can evaluate the specified
/// expression tree as type Ty instead of its larger type, and arrive with the
/// same value. This is used by code that tries to eliminate truncates.
///
/// This is a truncation operation if Ty is smaller than V->getType(), or a zero
/// extension operation if Ty is larger.
/// Ty will always be a type smaller than V. We should return true if trunc(V)
/// can be computed by computing V in the smaller type. If V is an instruction,
/// then trunc(inst(x,y)) can be computed as inst(trunc(x),trunc(y)), which only
/// makes sense if x and y can be efficiently truncated.
///
/// If CastOpc is a truncation, then Ty will be a type smaller than V. We
/// should return true if trunc(V) can be computed by computing V in the smaller
/// type. If V is an instruction, then trunc(inst(x,y)) can be computed as
/// inst(trunc(x),trunc(y)), which only makes sense if x and y can be
/// efficiently truncated.
///
/// If CastOpc is zext, we are asking if the low bits of the value can be
/// computed in a larger type, which is then and'd to get the final result.
static bool CanEvaluateInDifferentType(Value *V, const Type *Ty,
unsigned CastOpc,
unsigned &NumCastsRemoved) {
// FIXME: Eliminate CastOpc
assert(CastOpc == Instruction::Trunc);
static bool CanEvaluateTruncated(Value *V, const Type *Ty) {
// We can always evaluate constants in another type.
if (isa<Constant>(V))
return true;
@ -179,19 +166,10 @@ static bool CanEvaluateInDifferentType(Value *V, const Type *Ty,
const Type *OrigTy = V->getType();
// If this is an extension or truncate, we can often eliminate it.
if (isa<TruncInst>(I) || isa<ZExtInst>(I) || isa<SExtInst>(I)) {
// If this is a cast from the destination type, we can trivially eliminate
// it, and this will remove a cast overall.
if (I->getOperand(0)->getType() == Ty) {
// If the first operand is itself a cast, and is eliminable, do not count
// this as an eliminable cast. We would prefer to eliminate those two
// casts first.
if (!isa<CastInst>(I->getOperand(0)) && I->hasOneUse())
++NumCastsRemoved;
return true;
}
}
// If this is an extension from the dest type, we can eliminate it.
if ((isa<ZExtInst>(I) || isa<SExtInst>(I)) &&
I->getOperand(0)->getType() == Ty)
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.
@ -206,10 +184,8 @@ static bool CanEvaluateInDifferentType(Value *V, const Type *Ty,
case Instruction::Or:
case Instruction::Xor:
// These operators can all arbitrarily be extended or truncated.
return CanEvaluateInDifferentType(I->getOperand(0), Ty, CastOpc,
NumCastsRemoved) &&
CanEvaluateInDifferentType(I->getOperand(1), Ty, CastOpc,
NumCastsRemoved);
return CanEvaluateTruncated(I->getOperand(0), Ty) &&
CanEvaluateTruncated(I->getOperand(1), Ty);
case Instruction::UDiv:
case Instruction::URem: {
@ -220,10 +196,8 @@ static bool CanEvaluateInDifferentType(Value *V, const Type *Ty,
APInt Mask = APInt::getHighBitsSet(OrigBitWidth, OrigBitWidth-BitWidth);
if (MaskedValueIsZero(I->getOperand(0), Mask) &&
MaskedValueIsZero(I->getOperand(1), Mask)) {
return CanEvaluateInDifferentType(I->getOperand(0), Ty, CastOpc,
NumCastsRemoved) &&
CanEvaluateInDifferentType(I->getOperand(1), Ty, CastOpc,
NumCastsRemoved);
return CanEvaluateTruncated(I->getOperand(0), Ty) &&
CanEvaluateTruncated(I->getOperand(1), Ty);
}
}
break;
@ -233,10 +207,8 @@ static bool CanEvaluateInDifferentType(Value *V, const Type *Ty,
// constant amount, we can always perform a SHL in a smaller type.
if (ConstantInt *CI = dyn_cast<ConstantInt>(I->getOperand(1))) {
uint32_t BitWidth = Ty->getScalarSizeInBits();
if (BitWidth < OrigTy->getScalarSizeInBits() &&
CI->getLimitedValue(BitWidth) < BitWidth)
return CanEvaluateInDifferentType(I->getOperand(0), Ty, CastOpc,
NumCastsRemoved);
if (CI->getLimitedValue(BitWidth) < BitWidth)
return CanEvaluateTruncated(I->getOperand(0), Ty);
}
break;
case Instruction::LShr:
@ -246,34 +218,20 @@ static bool CanEvaluateInDifferentType(Value *V, const Type *Ty,
if (ConstantInt *CI = dyn_cast<ConstantInt>(I->getOperand(1))) {
uint32_t OrigBitWidth = OrigTy->getScalarSizeInBits();
uint32_t BitWidth = Ty->getScalarSizeInBits();
if (BitWidth < OrigBitWidth &&
MaskedValueIsZero(I->getOperand(0),
if (MaskedValueIsZero(I->getOperand(0),
APInt::getHighBitsSet(OrigBitWidth, OrigBitWidth-BitWidth)) &&
CI->getLimitedValue(BitWidth) < BitWidth) {
return CanEvaluateInDifferentType(I->getOperand(0), Ty, CastOpc,
NumCastsRemoved);
return CanEvaluateTruncated(I->getOperand(0), Ty);
}
}
break;
case Instruction::ZExt:
case Instruction::SExt:
case Instruction::Trunc:
// If this is the same kind of case as our original (e.g. zext+zext), we
// can safely replace it. Note that replacing it does not reduce the number
// of casts in the input.
if (Opc == CastOpc)
return true;
// sext (zext ty1), ty2 -> zext ty2
if (CastOpc == Instruction::SExt && Opc == Instruction::ZExt)
return true;
break;
// trunc(trunc(x)) -> trunc(x)
return true;
case Instruction::Select: {
SelectInst *SI = cast<SelectInst>(I);
return CanEvaluateInDifferentType(SI->getTrueValue(), Ty, CastOpc,
NumCastsRemoved) &&
CanEvaluateInDifferentType(SI->getFalseValue(), Ty, CastOpc,
NumCastsRemoved);
return CanEvaluateTruncated(SI->getTrueValue(), Ty) &&
CanEvaluateTruncated(SI->getFalseValue(), Ty);
}
case Instruction::PHI: {
// We can change a phi if we can change all operands. Note that we never
@ -281,8 +239,7 @@ static bool CanEvaluateInDifferentType(Value *V, const Type *Ty,
// instructions with a single use.
PHINode *PN = cast<PHINode>(I);
for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i)
if (!CanEvaluateInDifferentType(PN->getIncomingValue(i), Ty, CastOpc,
NumCastsRemoved))
if (!CanEvaluateTruncated(PN->getIncomingValue(i), Ty))
return false;
return true;
}
@ -515,10 +472,11 @@ static unsigned CanEvaluateSExtd(Value *V, const Type *Ty,
/// EvaluateInDifferentType - Given an expression that
/// CanEvaluateInDifferentType or CanEvaluateSExtd returns true for, actually
/// CanEvaluateTruncated or CanEvaluateSExtd returns true for, actually
/// insert the code to evaluate the expression.
Value *InstCombiner::EvaluateInDifferentType(Value *V, const Type *Ty,
bool isSigned) {
// FIXME: use libanalysis constant folding.
if (Constant *C = dyn_cast<Constant>(V))
return ConstantExpr::getIntegerCast(C, Ty, isSigned /*Sext or ZExt*/);
@ -699,8 +657,7 @@ Instruction *InstCombiner::commonIntCastTransforms(CastInst &CI) {
switch (CI.getOpcode()) {
default: assert(0 && "not an integer cast");
case Instruction::Trunc: {
if (!CanEvaluateInDifferentType(Src, DestTy,
Instruction::Trunc, NumCastsRemoved))
if (!CanEvaluateTruncated(Src, DestTy))
return 0;
// If this cast is a truncate, evaluting in a different type always