[PATCH] D118928: [FPEnv][InstSimplify] Fold fsub X, +0 ==> X

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

kpn created this revision.
kpn added reviewers: sepavloff, spatel, nlopes, lebedev.ri.
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Currently the fsub optimizations in InstSimplify don't know how to fold X - +0.0 to X when using the constrained intrinsics. This adds the support.

This review is split out from D107285 <https://reviews.llvm.org/D107285>.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D118928

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
@@ -27,11 +27,9 @@
   ret float %ret
 }
 
-; TODO: This will fold if we allow non-default floating point environments.
 define float @fsub_nnan_x_p0_ebmaytrap(float %a) #0 {
 ; CHECK-LABEL: @fsub_nnan_x_p0_ebmaytrap(
-; CHECK-NEXT:    [[RET:%.*]] = call nnan float @llvm.experimental.constrained.fsub.f32(float [[A:%.*]], float 0.000000e+00, metadata !"round.tonearest", metadata !"fpexcept.maytrap") #[[ATTR0]]
-; CHECK-NEXT:    ret float [[RET]]
+; CHECK-NEXT:    ret float [[A:%.*]]
 ;
   %ret = call nnan float @llvm.experimental.constrained.fsub.f32(float %a, float 0.0, metadata !"round.tonearest", metadata !"fpexcept.maytrap") #0
   ret float %ret
@@ -47,12 +45,11 @@
   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.
 define float @fsub_nnan_x_p0_ebstrict(float %a) #0 {
 ; CHECK-LABEL: @fsub_nnan_x_p0_ebstrict(
 ; CHECK-NEXT:    [[RET:%.*]] = call nnan float @llvm.experimental.constrained.fsub.f32(float [[A:%.*]], float 0.000000e+00, metadata !"round.tonearest", metadata !"fpexcept.strict") #[[ATTR0]]
-; CHECK-NEXT:    ret float [[RET]]
+; CHECK-NEXT:    ret float [[A]]
 ;
   %ret = call nnan float @llvm.experimental.constrained.fsub.f32(float %a, float 0.0, metadata !"round.tonearest", metadata !"fpexcept.strict") #0
   ret float %ret
Index: llvm/lib/Analysis/InstructionSimplify.cpp
===================================================================
--- llvm/lib/Analysis/InstructionSimplify.cpp
+++ llvm/lib/Analysis/InstructionSimplify.cpp
@@ -5130,13 +5130,14 @@
   if (Constant *C = simplifyFPOp({Op0, Op1}, FMF, Q, ExBehavior, Rounding))
     return C;
 
+  // fsub X, +0 ==> X
+  if (canIgnoreSNaN(ExBehavior, FMF))
+    if (match(Op1, m_PosZeroFP()))
+      return Op0;
+
   if (!isDefaultFPEnvironment(ExBehavior, Rounding))
     return nullptr;
 
-  // fsub X, +0 ==> X
-  if (match(Op1, m_PosZeroFP()))
-    return Op0;
-
   // fsub X, -0 ==> X, when we know X is not -0
   if (match(Op1, m_NegZeroFP()) &&
       (FMF.noSignedZeros() || CannotBeNegativeZero(Op0, Q.TLI)))


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