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Fold fptrunc(add (fpextend x), (fpextend y)) -> add(x,y), as GCC does.

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llvm-svn: 46406
This commit is contained in:
Chris Lattner 2008-01-27 05:29:54 +00:00
parent 00183edf55
commit aa553aa0c1
2 changed files with 111 additions and 3 deletions
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78
lib/Transforms/Scalar/InstructionCombining.cpp
View File

@ -203,7 +203,7 @@ namespace {
Instruction *visitTrunc(TruncInst &CI);
Instruction *visitZExt(ZExtInst &CI);
Instruction *visitSExt(SExtInst &CI);
Instruction *visitFPTrunc(CastInst &CI);
Instruction *visitFPTrunc(FPTruncInst &CI);
Instruction *visitFPExt(CastInst &CI);
Instruction *visitFPToUI(CastInst &CI);
Instruction *visitFPToSI(CastInst &CI);
@ -7141,8 +7141,80 @@ Instruction *InstCombiner::visitSExt(SExtInst &CI) {
return 0;
}
Instruction *InstCombiner::visitFPTrunc(CastInst &CI) {
return commonCastTransforms(CI);
/// FitsInFPType - Return a Constant* for the specified FP constant if it fits
/// in the specified FP type without changing its value.
static Constant *FitsInFPType(ConstantFP *CFP, const Type *FPTy,
const fltSemantics &Sem) {
APFloat F = CFP->getValueAPF();
if (F.convert(Sem, APFloat::rmNearestTiesToEven) == APFloat::opOK)
return ConstantFP::get(FPTy, F);
return 0;
}
/// LookThroughFPExtensions - If this is an fp extension instruction, look
/// through it until we get the source value.
static Value *LookThroughFPExtensions(Value *V) {
if (Instruction *I = dyn_cast<Instruction>(V))
if (I->getOpcode() == Instruction::FPExt)
return LookThroughFPExtensions(I->getOperand(0));
// If this value is a constant, return the constant in the smallest FP type
// that can accurately represent it. This allows us to turn
// (float)((double)X+2.0) into x+2.0f.
if (ConstantFP *CFP = dyn_cast<ConstantFP>(V)) {
if (CFP->getType() == Type::PPC_FP128Ty)
return V; // No constant folding of this.
// See if the value can be truncated to float and then reextended.
if (Value *V = FitsInFPType(CFP, Type::FloatTy, APFloat::IEEEsingle))
return V;
if (CFP->getType() == Type::DoubleTy)
return V; // Won't shrink.
if (Value *V = FitsInFPType(CFP, Type::DoubleTy, APFloat::IEEEdouble))
return V;
// Don't try to shrink to various long double types.
}
return V;
}
Instruction *InstCombiner::visitFPTrunc(FPTruncInst &CI) {
if (Instruction *I = commonCastTransforms(CI))
return I;
// If we have fptrunc(add (fpextend x), (fpextend y)), where x and y are
// smaller than the destination type, we can eliminate the truncate by doing
// the add as the smaller type. This applies to add/sub/mul/div as well as
// many builtins (sqrt, etc).
BinaryOperator *OpI = dyn_cast<BinaryOperator>(CI.getOperand(0));
if (OpI && OpI->hasOneUse()) {
switch (OpI->getOpcode()) {
default: break;
case Instruction::Add:
case Instruction::Sub:
case Instruction::Mul:
case Instruction::FDiv:
case Instruction::FRem:
const Type *SrcTy = OpI->getType();
Value *LHSTrunc = LookThroughFPExtensions(OpI->getOperand(0));
Value *RHSTrunc = LookThroughFPExtensions(OpI->getOperand(1));
if (LHSTrunc->getType() != SrcTy &&
RHSTrunc->getType() != SrcTy) {
unsigned DstSize = CI.getType()->getPrimitiveSizeInBits();
// If the source types were both smaller than the destination type of
// the cast, do this xform.
if (LHSTrunc->getType()->getPrimitiveSizeInBits() <= DstSize &&
RHSTrunc->getType()->getPrimitiveSizeInBits() <= DstSize) {
LHSTrunc = InsertCastBefore(Instruction::FPExt, LHSTrunc,
CI.getType(), CI);
RHSTrunc = InsertCastBefore(Instruction::FPExt, RHSTrunc,
CI.getType(), CI);
return BinaryOperator::create(OpI->getOpcode(), LHSTrunc, RHSTrunc);
}
}
break;
}
}
return 0;
}
Instruction *InstCombiner::visitFPExt(CastInst &CI) {

36
test/Transforms/InstCombine/fpextend.ll Normal file
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@ -0,0 +1,36 @@
; RUN: llvm-as < %s | opt -instcombine | llvm-dis | not grep fpext
@X = external global float
@Y = external global float
define void @test() nounwind {
entry:
%tmp = load float* @X, align 4 ; <float> [#uses=1]
%tmp1 = fpext float %tmp to double ; <double> [#uses=1]
%tmp3 = add double %tmp1, 0.000000e+00 ; <double> [#uses=1]
%tmp34 = fptrunc double %tmp3 to float ; <float> [#uses=1]
store float %tmp34, float* @X, align 4
ret void
}
define void @test3() nounwind {
entry:
%tmp = load float* @X, align 4 ; <float> [#uses=1]
%tmp1 = fpext float %tmp to double ; <double> [#uses=1]
%tmp2 = load float* @Y, align 4 ; <float> [#uses=1]
%tmp23 = fpext float %tmp2 to double ; <double> [#uses=1]
%tmp5 = fdiv double %tmp1, %tmp23 ; <double> [#uses=1]
%tmp56 = fptrunc double %tmp5 to float ; <float> [#uses=1]
store float %tmp56, float* @X, align 4
ret void
}
define void @test4() nounwind {
entry:
%tmp = load float* @X, align 4 ; <float> [#uses=1]
%tmp1 = fpext float %tmp to double ; <double> [#uses=1]
%tmp2 = sub double -0.000000e+00, %tmp1 ; <double> [#uses=1]
%tmp34 = fptrunc double %tmp2 to float ; <float> [#uses=1]
store float %tmp34, float* @X, align 4
ret void
}