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InstCombine: fold more cases of (fp_to_u/sint (u/sint_to_fp val))

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Fixes radar 15486701.

From: Fiona Glaser <fglaser@apple.com>

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@229437 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Mehdi Amini
2015-02-16 21:47:54 +00:00
parent be55a79941
commit e97c675022
3 changed files with 159 additions and 22 deletions
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70
lib/Transforms/InstCombine/InstCombineCasts.cpp
View File

@@ -1341,22 +1341,57 @@ Instruction *InstCombiner::visitFPExt(CastInst &CI) {
return commonCastTransforms(CI);
}
// fpto{s/u}i({u/s}itofp(X)) --> X or zext(X) or sext(X) or trunc(X)
// This is safe if the intermediate type has enough bits in its mantissa to
// accurately represent all values of X. For example, this won't work with
// i64 -> float -> i64.
Instruction *InstCombiner::FoldItoFPtoI(Instruction &FI) {
if (!isa<UIToFPInst>(FI.getOperand(0)) && !isa<SIToFPInst>(FI.getOperand(0)))
return nullptr;
Instruction *OpI = cast<Instruction>(FI.getOperand(0));
Value *SrcI = OpI->getOperand(0);
Type *FITy = FI.getType();
Type *OpITy = OpI->getType();
Type *SrcTy = SrcI->getType();
bool IsInputSigned = isa<SIToFPInst>(OpI);
bool IsOutputSigned = isa<FPToSIInst>(FI);
// We can safely assume the conversion won't overflow the output range,
// because (for example) (uint8_t)18293.f is undefined behavior.
// Since we can assume the conversion won't overflow, our decision as to
// whether the input will fit in the float should depend on the minimum
// of the input range and output range.
// This means this is also safe for a signed input and unsigned output, since
// a negative input would lead to undefined behavior.
int InputSize = (int)SrcTy->getScalarSizeInBits() - IsInputSigned;
int OutputSize = (int)FITy->getScalarSizeInBits() - IsOutputSigned;
int ActualSize = std::min(InputSize, OutputSize);
if (ActualSize <= OpITy->getFPMantissaWidth()) {
if (FITy->getScalarSizeInBits() > SrcTy->getScalarSizeInBits()) {
if (IsInputSigned && IsOutputSigned)
return new SExtInst(SrcI, FITy);
return new ZExtInst(SrcI, FITy);
}
if (FITy->getScalarSizeInBits() < SrcTy->getScalarSizeInBits())
return new TruncInst(SrcI, FITy);
if (SrcTy == FITy)
return ReplaceInstUsesWith(FI, SrcI);
return new BitCastInst(SrcI, FITy);
}
return nullptr;
}
Instruction *InstCombiner::visitFPToUI(FPToUIInst &FI) {
Instruction *OpI = dyn_cast<Instruction>(FI.getOperand(0));
if (!OpI)
return commonCastTransforms(FI);
// fptoui(uitofp(X)) --> X
// fptoui(sitofp(X)) --> X
// This is safe if the intermediate type has enough bits in its mantissa to
// accurately represent all values of X. For example, do not do this with
// i64->float->i64. This is also safe for sitofp case, because any negative
// 'X' value would cause an undefined result for the fptoui.
if ((isa<UIToFPInst>(OpI) || isa<SIToFPInst>(OpI)) &&
OpI->getOperand(0)->getType() == FI.getType() &&
(int)FI.getType()->getScalarSizeInBits() < /*extra bit for sign */
OpI->getType()->getFPMantissaWidth())
return ReplaceInstUsesWith(FI, OpI->getOperand(0));
if (Instruction *I = FoldItoFPtoI(FI))
return I;
return commonCastTransforms(FI);
}
@@ -1366,17 +1401,8 @@ Instruction *InstCombiner::visitFPToSI(FPToSIInst &FI) {
if (!OpI)
return commonCastTransforms(FI);
// fptosi(sitofp(X)) --> X
// fptosi(uitofp(X)) --> X
// This is safe if the intermediate type has enough bits in its mantissa to
// accurately represent all values of X. For example, do not do this with
// i64->float->i64. This is also safe for sitofp case, because any negative
// 'X' value would cause an undefined result for the fptoui.
if ((isa<UIToFPInst>(OpI) || isa<SIToFPInst>(OpI)) &&
OpI->getOperand(0)->getType() == FI.getType() &&
(int)FI.getType()->getScalarSizeInBits() <=
OpI->getType()->getFPMantissaWidth())
return ReplaceInstUsesWith(FI, OpI->getOperand(0));
if (Instruction *I = FoldItoFPtoI(FI))
return I;
return commonCastTransforms(FI);
}

1
lib/Transforms/InstCombine/InstCombineInternal.h
View File

@@ -245,6 +245,7 @@ public:
Instruction *FoldSPFofSPF(Instruction *Inner, SelectPatternFlavor SPF1,
Value *A, Value *B, Instruction &Outer,
SelectPatternFlavor SPF2, Value *C);
Instruction *FoldItoFPtoI(Instruction &FI);
Instruction *visitSelectInst(SelectInst &SI);
Instruction *visitSelectInstWithICmp(SelectInst &SI, ICmpInst *ICI);
Instruction *visitCallInst(CallInst &CI);