[PATCH] D123830: [InstCombine] Complete folding of fneg-of-fabs

[Chenbing.Zheng via Phabricator via llvm-commits]

Chenbing.Zheng updated this revision to Diff 423801.
Chenbing.Zheng retitled this revision from "[InstCombine]  Optimize folding of fneg-of-fabs" to "[InstCombine]  Complete folding of fneg-of-fabs".
Chenbing.Zheng edited the summary of this revision.
Chenbing.Zheng added a comment.

address comments


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D123830/new/

https://reviews.llvm.org/D123830

Files:
  llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp
  llvm/test/Transforms/InstCombine/fneg.ll


Index: llvm/test/Transforms/InstCombine/fneg.ll
===================================================================
--- llvm/test/Transforms/InstCombine/fneg.ll
+++ llvm/test/Transforms/InstCombine/fneg.ll
@@ -714,13 +714,10 @@
   ret float %fneg1
 }
 
-; TODO: This should reduce to fneg-of-fabs.
-
 define float @fnabs(float %a) {
 ; CHECK-LABEL: @fnabs(
-; CHECK-NEXT:    [[CMP:%.*]] = fcmp olt float [[A:%.*]], 0.000000e+00
-; CHECK-NEXT:    [[A_NEG:%.*]] = fneg fast float [[A]]
-; CHECK-NEXT:    [[FNEG1:%.*]] = select fast i1 [[CMP]], float [[A]], float [[A_NEG]]
+; CHECK-NEXT:    [[TMP1:%.*]] = call fast float @llvm.fabs.f32(float [[A:%.*]])
+; CHECK-NEXT:    [[FNEG1:%.*]] = fneg fast float [[TMP1]]
 ; CHECK-NEXT:    ret float [[FNEG1]]
 ;
   %fneg = fneg float %a
@@ -732,6 +729,19 @@
 
 define float @fnabs_1(float %a) {
 ; CHECK-LABEL: @fnabs_1(
+; CHECK-NEXT:    [[TMP1:%.*]] = call fast float @llvm.fabs.f32(float [[A:%.*]])
+; CHECK-NEXT:    [[FNEG1:%.*]] = fneg fast float [[TMP1]]
+; CHECK-NEXT:    ret float [[FNEG1]]
+;
+  %fneg = fneg float %a
+  %cmp = fcmp ogt float %a, %fneg
+  %sel = select i1 %cmp, float %a, float %fneg
+  %fneg1 = fneg fast float %sel
+  ret float %fneg1
+}
+
+define float @fnabs_2(float %a) {
+; CHECK-LABEL: @fnabs_2(
 ; CHECK-NEXT:    [[TMP1:%.*]] = call nsz float @llvm.fabs.f32(float [[A:%.*]])
 ; CHECK-NEXT:    [[FNEG1:%.*]] = fneg float [[TMP1]]
 ; CHECK-NEXT:    ret float [[FNEG1]]
Index: llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp
===================================================================
--- llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp
+++ llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp
@@ -2809,6 +2809,30 @@
     Value *Fabs = Builder.CreateUnaryIntrinsic(Intrinsic::fabs, TrueVal, &SI);
     return replaceInstUsesWith(SI, Fabs);
   }
+  // With nnan and nsz
+  // (X <   +/-0.0) ? X : -X --> -fabs(x)
+  // (X <=  +/-0.0) ? X : -X --> -fabs(x)
+  if (match(CondVal, m_FCmp(Pred, m_Specific(TrueVal), m_AnyZeroFP())) &&
+      match(FalseVal, m_FNeg(m_Specific(TrueVal))) && SI.hasNoSignedZeros() &&
+      (Pred == FCmpInst::FCMP_OLT || Pred == FCmpInst::FCMP_OLE ||
+       Pred == FCmpInst::FCMP_ULT || Pred == FCmpInst::FCMP_ULE)) {
+    Value *Fabs = Builder.CreateUnaryIntrinsic(Intrinsic::fabs, TrueVal, &SI);
+    Instruction *NewFNeg = UnaryOperator::CreateFNeg(Fabs);
+    NewFNeg->setFastMathFlags(SI.getFastMathFlags());
+    return NewFNeg;
+  }
+  // With nnan and nsz
+  // (X >   +/-0.0) ? -X : X --> -fabs(x)
+  // (X >=  +/-0.0) ? -X : X --> -fabs(x)
+  if (match(CondVal, m_FCmp(Pred, m_Specific(FalseVal), m_AnyZeroFP())) &&
+      match(TrueVal, m_FNeg(m_Specific(FalseVal))) && SI.hasNoSignedZeros() &&
+      (Pred == FCmpInst::FCMP_OGT || Pred == FCmpInst::FCMP_OGE ||
+       Pred == FCmpInst::FCMP_UGT || Pred == FCmpInst::FCMP_UGE)) {
+    Value *Fabs = Builder.CreateUnaryIntrinsic(Intrinsic::fabs, FalseVal, &SI);
+    Instruction *NewFNeg = UnaryOperator::CreateFNeg(Fabs);
+    NewFNeg->setFastMathFlags(SI.getFastMathFlags());
+    return NewFNeg;
+  }
 
   // See if we are selecting two values based on a comparison of the two values.
   if (ICmpInst *ICI = dyn_cast<ICmpInst>(CondVal))


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