[PATCH] D123396: [FPEnv][InstSimplify] Fold fsub -0.0, -X ==> X

[Kevin P. Neal via Phabricator via llvm-commits]

This revision was landed with ongoing or failed builds.
This revision was automatically updated to reflect the committed changes.
Closed by commit rGd43d9e1d5c98: [FPEnv][InstSimplify] Fold fsub -0.0, -X ==> X (authored by kpn).

Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D123396/new/

https://reviews.llvm.org/D123396

Files:
  llvm/lib/Analysis/InstructionSimplify.cpp
  llvm/test/Transforms/InstSimplify/strictfp-fsub.ll


Index: llvm/test/Transforms/InstSimplify/strictfp-fsub.ll
===================================================================
--- llvm/test/Transforms/InstSimplify/strictfp-fsub.ll
+++ llvm/test/Transforms/InstSimplify/strictfp-fsub.ll
@@ -251,12 +251,9 @@
   ret float %ret
 }
 
-; TODO: This will fold if we allow non-default floating point environments.
 define float @fsub_fneg_nnan_n0_fnX_ebmaytrap(float %a) #0 {
 ; CHECK-LABEL: @fsub_fneg_nnan_n0_fnX_ebmaytrap(
-; CHECK-NEXT:    [[NEGA:%.*]] = fneg float [[A:%.*]]
-; CHECK-NEXT:    [[RET:%.*]] = call nnan float @llvm.experimental.constrained.fsub.f32(float -0.000000e+00, float [[NEGA]], metadata !"round.tonearest", metadata !"fpexcept.maytrap") #[[ATTR0]]
-; CHECK-NEXT:    ret float [[RET]]
+; CHECK-NEXT:    ret float [[A:%.*]]
 ;
   %nega = fneg float %a
   %ret = call nnan float @llvm.experimental.constrained.fsub.f32(float -0.0, float %nega, metadata !"round.tonearest", metadata !"fpexcept.maytrap") #0
@@ -275,13 +272,12 @@
   ret float %ret
 }
 
-; TODO: This will fold if we allow non-default floating point environments.
-; TODO: The instruction is expected to remain, but the result isn't used.
+; NOTE: The instruction is expected to remain, but the result isn't used.
 define float @fsub_fneg_nnan_n0_fnX_ebstrict(float %a) #0 {
 ; CHECK-LABEL: @fsub_fneg_nnan_n0_fnX_ebstrict(
 ; CHECK-NEXT:    [[NEGA:%.*]] = fneg float [[A:%.*]]
 ; CHECK-NEXT:    [[RET:%.*]] = call nnan float @llvm.experimental.constrained.fsub.f32(float -0.000000e+00, float [[NEGA]], metadata !"round.tonearest", metadata !"fpexcept.strict") #[[ATTR0]]
-; CHECK-NEXT:    ret float [[RET]]
+; CHECK-NEXT:    ret float [[A]]
 ;
   %nega = fneg float %a
   %ret = call nnan float @llvm.experimental.constrained.fsub.f32(float -0.0, float %nega, metadata !"round.tonearest", metadata !"fpexcept.strict") #0
Index: llvm/lib/Analysis/InstructionSimplify.cpp
===================================================================
--- llvm/lib/Analysis/InstructionSimplify.cpp
+++ llvm/lib/Analysis/InstructionSimplify.cpp
@@ -5207,15 +5207,16 @@
         (FMF.noSignedZeros() || CannotBeNegativeZero(Op0, Q.TLI)))
       return Op0;
 
-  if (!isDefaultFPEnvironment(ExBehavior, Rounding))
-    return nullptr;
-
   // fsub -0.0, (fsub -0.0, X) ==> X
   // fsub -0.0, (fneg X) ==> X
   Value *X;
-  if (match(Op0, m_NegZeroFP()) &&
-      match(Op1, m_FNeg(m_Value(X))))
-    return X;
+  if (canIgnoreSNaN(ExBehavior, FMF))
+    if (match(Op0, m_NegZeroFP()) &&
+        match(Op1, m_FNeg(m_Value(X))))
+      return X;
+
+  if (!isDefaultFPEnvironment(ExBehavior, Rounding))
+    return nullptr;
 
   // fsub 0.0, (fsub 0.0, X) ==> X if signed zeros are ignored.
   // fsub 0.0, (fneg X) ==> X if signed zeros are ignored.


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