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[InstCombine] Add fold for fabs(-x) -> fabs(x) #94183

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[InstCombine] Add fold for fabs(-x) -> fabs(x) #94183

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[InstCombine] Add fold for fabs(-x) -> fabs(x)
VaibhavRumale Jun 3, 2024
73d52ca
Merge branch 'main' into main
VaibhavRumale Jun 3, 2024
267f9b5
Merge branch 'llvm:main' into main
VaibhavRumale Jun 4, 2024
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7 changes: 7 additions & 0 deletions llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
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Expand Up @@ -2517,6 +2517,13 @@ Instruction *InstCombinerImpl::visitCallInst(CallInst &CI) {
}
case Intrinsic::fabs: {
Value *Cond, *TVal, *FVal;
Value* Arg = II->getArgOperand(0);
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Can you replace all following uses of II->getArgOperand(0) with Arg?

Value* X;
// fabs (-X) --> fabs (X)
if (match(Arg, m_FNeg(m_Value(X)))) {
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Please drop the braces.
See https://llvm.org/docs/CodingStandards.html#don-t-use-braces-on-simple-single-statement-bodies-of-if-else-loop-statements

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Somewhere is a strip sign operations helper function that also covers copysign

return replaceInstUsesWith(CI, Builder.CreateUnaryIntrinsic(Intrinsic::fabs, X));
}

if (match(II->getArgOperand(0),
m_Select(m_Value(Cond), m_Value(TVal), m_Value(FVal)))) {
// fabs (select Cond, TrueC, FalseC) --> select Cond, AbsT, AbsF
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57 changes: 57 additions & 0 deletions llvm/test/Transforms/InstCombine/fabs-fneg-fold.ll
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@@ -0,0 +1,57 @@
; RUN: opt -S -passes=instcombine %s | FileCheck %s
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Please regenerate check lines with llvm/utils/update_test_checks.py


define float @fabs_fneg_f32(float %x) {
; CHECK-LABEL: define float @fabs_fneg_f32(
; CHECK-NEXT: [[FABS:%.*]] = call float @llvm.fabs.f32(float [[X:%.*]])
; CHECK-NEXT: ret float [[FABS]]
;
%neg = fneg float %x
%fabs = call float @llvm.fabs.f32(float %neg)
ret float %fabs
}

define <2 x float> @fabs_fneg_v2f32(<2 x float> %x) {
; CHECK-LABEL: define <2 x float> @fabs_fneg_v2f32(
; CHECK-NEXT: [[FABS:%.*]] = call <2 x float> @llvm.fabs.v2f32(<2 x float> [[X:%.*]])
; CHECK-NEXT: ret <2 x float> [[FABS]]
;
%neg = fneg <2 x float> %x
%fabs = call <2 x float> @llvm.fabs.v2f32(<2 x float> %neg)
ret <2 x float> %fabs
}

define double @fabs_fneg_f64(double %x) {
; CHECK-LABEL: define double @fabs_fneg_f64(
; CHECK-NEXT: [[FABS:%.*]] = call double @llvm.fabs.f64(double [[X:%.*]])
; CHECK-NEXT: ret double [[FABS]]
;
%neg = fneg double %x
%fabs = call double @llvm.fabs.f64(double %neg)
ret double %fabs
}

define <4 x double> @fabs_fneg_v4f64(<4 x double> %x) {
; CHECK-LABEL: define <4 x double> @fabs_fneg_v4f64(
; CHECK-NEXT: [[FABS:%.*]] = call <4 x double> @llvm.fabs.v4f64(<4 x double> [[X:%.*]])
; CHECK-NEXT: ret <4 x double> [[FABS]]
;
%neg = fneg <4 x double> %x
%fabs = call <4 x double> @llvm.fabs.v4f64(<4 x double> %neg)
ret <4 x double> %fabs
}

define half @fabs_fneg_f16(half %x) {
; CHECK-LABEL: define half @fabs_fneg_f16(
; CHECK-NEXT: [[FABS:%.*]] = call half @llvm.fabs.f16(half [[X:%.*]])
; CHECK-NEXT: ret half [[FABS]]
;
%neg = fneg half %x
%fabs = call half @llvm.fabs.f16(half %neg)
ret half %fabs
}

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Should test flag preservation behavior

declare float @llvm.fabs.f32(float)
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These declarations are unnecessary.

declare <2 x float> @llvm.fabs.v2f32(<2 x float>)
declare double @llvm.fabs.f64(double)
declare <4 x double> @llvm.fabs.v4f64(<4 x double>)
declare half @llvm.fabs.f16(half)
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