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InstCombine: If the divisor of an fdiv has an exact inverse, turn it into an fmul.

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Fixes PR9587.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@128546 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Benjamin Kramer 2011-03-30 15:42:35 +00:00
parent 2746000f4f
commit 546739656e
2 changed files with 37 additions and 0 deletions
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12
lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
View File

@ -452,6 +452,18 @@ Instruction *InstCombiner::visitFDiv(BinaryOperator &I) {
if (Value *V = SimplifyFDivInst(Op0, Op1, TD))
return ReplaceInstUsesWith(I, V);
if (ConstantFP *Op1C = dyn_cast<ConstantFP>(Op1)) {
const APFloat &Op1F = Op1C->getValueAPF();
// If the divisor has an exact multiplicative inverse we can turn the fdiv
// into a cheaper fmul.
APFloat Reciprocal(Op1F.getSemantics());
if (Op1F.getExactInverse(&Reciprocal)) {
ConstantFP *RFP = ConstantFP::get(Builder->getContext(), Reciprocal);
return BinaryOperator::CreateFMul(Op0, RFP);
}
}
return 0;
}

25
test/Transforms/InstCombine/fdiv.ll Normal file
View File

@ -0,0 +1,25 @@
; RUN: opt -S -instcombine < %s | FileCheck %s
define float @test1(float %x) nounwind readnone ssp {
%div = fdiv float %x, 0x3810000000000000
ret float %div
; CHECK: @test1
; CHECK-NEXT: fmul float %x, 0x47D0000000000000
}
define float @test2(float %x) nounwind readnone ssp {
%div = fdiv float %x, 0x47E0000000000000
ret float %div
; CHECK: @test2
; CHECK-NEXT: fmul float %x, 0x3800000000000000
}
define float @test3(float %x) nounwind readnone ssp {
%div = fdiv float %x, 0x36A0000000000000
ret float %div
; CHECK: @test3
; CHECK-NEXT: fdiv float %x, 0x36A0000000000000
}