[InstCombine] Add one-use check when folding fabs over selects (llvm#122270)

Fixes multi-use issue introduced by
llvm#86390.
It allows the folding of `fabs (select Cond, TrueC, FalseC)` to avoid performance regression in ocio

Author: dtcxzyw

llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp

@@ -2752,7 +2752,8 @@ 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);

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
+}