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InstCombine: Move (sext icmp) transforms into their own method. No intended functionality change. 

llvm-svn: 128731
This commit is contained in:
Benjamin Kramer 2011-04-01 20:09:03 +00:00
parent 8b1bca1998
commit 398b8c5faf
2 changed files with 43 additions and 37 deletions
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1
llvm/lib/Transforms/InstCombine/InstCombine.h
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@ -217,6 +217,7 @@ private:
Instruction *transformCallThroughTrampoline(CallSite CS);
Instruction *transformZExtICmp(ICmpInst *ICI, Instruction &CI,
bool DoXform = true);
Instruction *transformSExtICmp(ICmpInst *ICI, Instruction &CI);
bool WillNotOverflowSignedAdd(Value *LHS, Value *RHS);
Value *EmitGEPOffset(User *GEP);

79
llvm/lib/Transforms/InstCombine/InstCombineCasts.cpp
View File

@ -876,6 +876,46 @@ Instruction *InstCombiner::visitZExt(ZExtInst &CI) {
return 0;
}
/// transformSExtICmp - Transform (sext icmp) to bitwise / integer operations
/// in order to eliminate the icmp.
Instruction *InstCombiner::transformSExtICmp(ICmpInst *ICI, Instruction &CI) {
Value *Op0 = ICI->getOperand(0), *Op1 = ICI->getOperand(1);
ICmpInst::Predicate Pred = ICI->getPredicate();
if (ConstantInt *Op1C = dyn_cast<ConstantInt>(Op1)) {
// (x <s 0) ? -1 : 0 -> ashr x, 31 -> all ones if signed
// (x >s -1) ? -1 : 0 -> ashr x, 31 -> all ones if not signed
if ((Pred == ICmpInst::ICMP_SLT && Op1C->isZero()) ||
(Pred == ICmpInst::ICMP_SGT && Op1C->isAllOnesValue())) {
Value *Sh = ConstantInt::get(Op0->getType(),
Op0->getType()->getScalarSizeInBits()-1);
Value *In = Builder->CreateAShr(Op0, Sh, Op0->getName()+".lobit");
if (In->getType() != CI.getType())
In = Builder->CreateIntCast(In, CI.getType(), true/*SExt*/, "tmp");
if (Pred == ICmpInst::ICMP_SGT)
In = Builder->CreateNot(In, In->getName()+".not");
return ReplaceInstUsesWith(CI, In);
}
}
// vector (x <s 0) ? -1 : 0 -> ashr x, 31 -> all ones if signed.
if (const VectorType *VTy = dyn_cast<VectorType>(CI.getType())) {
if (Pred == ICmpInst::ICMP_SLT && match(Op1, m_Zero()) &&
Op0->getType() == CI.getType()) {
const Type *EltTy = VTy->getElementType();
// splat the shift constant to a constant vector.
Constant *VSh = ConstantInt::get(VTy, EltTy->getScalarSizeInBits()-1);
Value *In = Builder->CreateAShr(Op0, VSh, Op0->getName()+".lobit");
return ReplaceInstUsesWith(CI, In);
}
}
return 0;
}
/// CanEvaluateSExtd - Return true if we can take the specified value
/// and return it as type Ty without inserting any new casts and without
/// changing the value of the common low bits. This is used by code that tries
@ -999,44 +1039,9 @@ Instruction *InstCombiner::visitSExt(SExtInst &CI) {
Value *Res = Builder->CreateShl(TI->getOperand(0), ShAmt, "sext");
return BinaryOperator::CreateAShr(Res, ShAmt);
}
// (x <s 0) ? -1 : 0 -> ashr x, 31 -> all ones if signed
// (x >s -1) ? -1 : 0 -> ashr x, 31 -> all ones if not signed
{
ICmpInst::Predicate Pred; Value *CmpLHS; ConstantInt *CmpRHS;
if (match(Src, m_ICmp(Pred, m_Value(CmpLHS), m_ConstantInt(CmpRHS)))) {
// sext (x <s 0) to i32 --> x>>s31 true if signbit set.
// sext (x >s -1) to i32 --> (x>>s31)^-1 true if signbit clear.
if ((Pred == ICmpInst::ICMP_SLT && CmpRHS->isZero()) ||
(Pred == ICmpInst::ICMP_SGT && CmpRHS->isAllOnesValue())) {
Value *Sh = ConstantInt::get(CmpLHS->getType(),
CmpLHS->getType()->getScalarSizeInBits()-1);
Value *In = Builder->CreateAShr(CmpLHS, Sh, CmpLHS->getName()+".lobit");
if (In->getType() != CI.getType())
In = Builder->CreateIntCast(In, CI.getType(), true/*SExt*/, "tmp");
if (Pred == ICmpInst::ICMP_SGT)
In = Builder->CreateNot(In, In->getName()+".not");
return ReplaceInstUsesWith(CI, In);
}
}
}
// vector (x <s 0) ? -1 : 0 -> ashr x, 31 -> all ones if signed.
if (const VectorType *VTy = dyn_cast<VectorType>(DestTy)) {
ICmpInst::Predicate Pred; Value *CmpLHS;
if (match(Src, m_ICmp(Pred, m_Value(CmpLHS), m_Zero()))) {
if (Pred == ICmpInst::ICMP_SLT && CmpLHS->getType() == DestTy) {
const Type *EltTy = VTy->getElementType();
// splat the shift constant to a constant vector.
Constant *VSh = ConstantInt::get(VTy, EltTy->getScalarSizeInBits()-1);
Value *In = Builder->CreateAShr(CmpLHS, VSh,CmpLHS->getName()+".lobit");
return ReplaceInstUsesWith(CI, In);
}
}
}
if (ICmpInst *ICI = dyn_cast<ICmpInst>(Src))
return transformSExtICmp(ICI, CI);
// If the input is a shl/ashr pair of a same constant, then this is a sign
// extension from a smaller value. If we could trust arbitrary bitwidth