[llvm] d43d9e1 - [FPEnv][InstSimplify] Fold fsub -0.0, -X ==> X

[Kevin P. Neal via llvm-commits]

Author: Kevin P. Neal
Date: 2022-04-14T11:48:54-04:00
New Revision: d43d9e1d5c98e64db1054b4fb91d044299d3f717

URL: https://github.com/llvm/llvm-project/commit/d43d9e1d5c98e64db1054b4fb91d044299d3f717
DIFF: https://github.com/llvm/llvm-project/commit/d43d9e1d5c98e64db1054b4fb91d044299d3f717.diff

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

Currently the fsub optimizations in InstSimplify don't know how to fold
-0.0 - (-X) to X when the constrained intrinsics are used. This adds partial
support. The rest of the support will come later with work on the IR
matchers.

This review is split out from D107285.

Differential Revision: https://reviews.llvm.org/D123396

Added: 
    

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

Removed: 
    


################################################################################
diff  --git a/llvm/lib/Analysis/InstructionSimplify.cpp b/llvm/lib/Analysis/InstructionSimplify.cpp
index 4efc7c3050bb4..c299ef3458fee 100644
--- a/llvm/lib/Analysis/InstructionSimplify.cpp
+++ b/llvm/lib/Analysis/InstructionSimplify.cpp
@@ -5207,15 +5207,16 @@ SimplifyFSubInst(Value *Op0, Value *Op1, FastMathFlags FMF,
         (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.

diff  --git a/llvm/test/Transforms/InstSimplify/strictfp-fsub.ll b/llvm/test/Transforms/InstSimplify/strictfp-fsub.ll
index ef6010e7de849..801b2a1b44be3 100644
--- a/llvm/test/Transforms/InstSimplify/strictfp-fsub.ll
+++ b/llvm/test/Transforms/InstSimplify/strictfp-fsub.ll
@@ -251,12 +251,9 @@ define float @fsub_fneg_n0_fnX_ebmaytrap(float %a) #0 {
   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 @@ define float @fsub_fneg_n0_fnX_ebstrict(float %a) #0 {
   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