[InstCombine] Add one-use check when folding fabs over selects #122270
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This was referenced Jan 9, 2025
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@llvm/pr-subscribers-llvm-transforms Author: Yingwei Zheng (dtcxzyw) ChangesFixes multi-use issue introduced by #86390. Full diff: https://github.com/llvm/llvm-project/pull/122270.diff 2 Files Affected:
diff --git a/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp b/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
index c55c40c88bc845..a19eded6565997 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
@@ -2709,7 +2709,8 @@ Instruction *InstCombinerImpl::visitCallInst(CallInst &CI) {
if (match(Arg, m_Select(m_Value(Cond), m_Value(TVal), m_Value(FVal)))) {
// fabs (select Cond, TrueC, FalseC) --> select Cond, AbsT, AbsF
- if (isa<Constant>(TVal) || isa<Constant>(FVal)) {
+ if (Arg->hasOneUse() ? (isa<Constant>(TVal) || isa<Constant>(FVal))
+ : (isa<Constant>(TVal) && isa<Constant>(FVal))) {
CallInst *AbsT = Builder.CreateCall(II->getCalledFunction(), {TVal});
CallInst *AbsF = Builder.CreateCall(II->getCalledFunction(), {FVal});
SelectInst *SI = SelectInst::Create(Cond, AbsT, AbsF);
diff --git a/llvm/test/Transforms/InstCombine/intrinsic-select.ll b/llvm/test/Transforms/InstCombine/intrinsic-select.ll
index 4ce2908a630785..a8117ce663a6d0 100644
--- a/llvm/test/Transforms/InstCombine/intrinsic-select.ll
+++ b/llvm/test/Transforms/InstCombine/intrinsic-select.ll
@@ -2,6 +2,7 @@
; RUN: opt -passes=instcombine -S < %s | FileCheck %s
declare void @use(i32)
+declare void @usef32(float)
declare i32 @llvm.ctlz.i32(i32, i1)
declare <3 x i17> @llvm.ctlz.v3i17(<3 x i17>, i1)
@@ -344,3 +345,29 @@ define double @test_fabs_select_fmf2(i1 %cond, double %a) {
%fabs = call nnan ninf nsz double @llvm.fabs.f64(double %sel1)
ret double %fabs
}
+
+define float @test_fabs_select_multiuse(i1 %cond, float %x) {
+; CHECK-LABEL: @test_fabs_select_multiuse(
+; CHECK-NEXT: [[SELECT:%.*]] = select i1 [[COND:%.*]], float [[X:%.*]], float 0x7FF0000000000000
+; CHECK-NEXT: call void @usef32(float [[SELECT]])
+; CHECK-NEXT: [[FABS:%.*]] = call float @llvm.fabs.f32(float [[SELECT]])
+; CHECK-NEXT: ret float [[FABS]]
+;
+ %select = select i1 %cond, float %x, float 0x7FF0000000000000
+ call void @usef32(float %select)
+ %fabs = call float @llvm.fabs.f32(float %select)
+ ret float %fabs
+}
+
+define float @test_fabs_select_multiuse_both_constant(i1 %cond, float %x) {
+; CHECK-LABEL: @test_fabs_select_multiuse_both_constant(
+; CHECK-NEXT: [[SELECT:%.*]] = select i1 [[COND:%.*]], float -1.000000e+00, float -2.000000e+00
+; CHECK-NEXT: call void @usef32(float [[SELECT]])
+; CHECK-NEXT: [[FABS:%.*]] = select i1 [[COND]], float 1.000000e+00, float 2.000000e+00
+; CHECK-NEXT: ret float [[FABS]]
+;
+ %select = select i1 %cond, float -1.0, float -2.0
+ call void @usef32(float %select)
+ %fabs = call float @llvm.fabs.f32(float %select)
+ ret float %fabs
+}
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Collaborator
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LLVM Buildbot has detected a new failure on builder Full details are available at: https://lab.llvm.org/buildbot/#/builders/73/builds/12661 Here is the relevant piece of the build log for the reference |
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Fixes multi-use issue introduced by #86390.
It also forbids the folding offabs (select Cond, TrueC, FalseC)when select has external uses.fabsis always cheaper than a select with constant arms.Update: allow this to fix a regression in ocio