[FPEnv][InstSimplify] 0.0 - -X ==> X

[kpn]

Summary

Another ticket split out of D107285, this extends the optimization of 0.0 - -X to just X when using constrained intrinsics and the optimization is allowed.

If the negation of X is done with fsub then the match fails because of the lack of IR Matcher support for constrained intrinsics.

While I'm here, remove some TODO notices since the work is no longer planned.

[spatel]

LGTM

llvm/test/Transforms/InstSimplify/strictfp-fsub.ll

396–397

Remove this TODO line?

llvm/lib/Analysis/InstructionSimplify.cpp

simplifyFSubInst(Value *Op0, Value *Op1, FastMathFlags FMF,
 
   // fsub -0.0, (fsub -0.0, X) ==> X
   // fsub -0.0, (fneg X) ==> X
   Value *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.
+  if (canIgnoreSNaN(ExBehavior, FMF))
      if (FMF.noSignedZeros() && match(Op0, m_AnyZeroFP()) &&
          (match(Op1, m_FSub(m_AnyZeroFP(), m_Value(X))) ||
           match(Op1, m_FNeg(m_Value(X)))))
        return X;
 
+  if (!isDefaultFPEnvironment(ExBehavior, Rounding))
+    return nullptr;
+
   // fsub nnan x, x ==> 0.0
   if (FMF.noNaNs() && Op0 == Op1)
     return Constant::getNullValue(Op0->getType());
 
   // Y - (Y - X) --> X
   // (X + Y) - Y --> X
   if (FMF.noSignedZeros() && FMF.allowReassoc() &&
       (match(Op1, m_FSub(m_Specific(Op0), m_Value(X))) ||

llvm/test/Transforms/InstSimplify/strictfp-fsub.ll

 ; CHECK-LABEL: @fsub_x_p0_ebstrict(
 ; CHECK-NEXT:    [[RET:%.*]] = call float @llvm.experimental.constrained.fsub.f32(float [[A:%.*]], float 0.000000e+00, metadata !"round.tonearest", metadata !"fpexcept.strict") #[[ATTR0]]
 ; CHECK-NEXT:    ret float [[RET]]
 ;
   %ret = call float @llvm.experimental.constrained.fsub.f32(float %a, float 0.0, metadata !"round.tonearest", metadata !"fpexcept.strict") #0
   ret float %ret
 }
 
-; TODO: The instruction is expected to remain, but the result isn't used.
+; 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 [[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
 }

 ; CHECK-LABEL: @fold_fsub_nsz_x_n0_ebstrict(
 ; CHECK-NEXT:    [[SUB:%.*]] = call nsz float @llvm.experimental.constrained.fsub.f32(float [[A:%.*]], float -0.000000e+00, metadata !"round.tonearest", metadata !"fpexcept.strict") #[[ATTR0]]
 ; CHECK-NEXT:    ret float [[SUB]]
 ;
   %sub = call nsz float @llvm.experimental.constrained.fsub.f32(float %a, float -0.0, metadata !"round.tonearest", metadata !"fpexcept.strict") #0
   ret float %sub
 }
 
-; TODO: The instruction is expected to remain, but the result isn't used.
+; The instruction is expected to remain, but the result isn't used.
 define float @fold_fsub_nsz_nnan_x_n0_ebstrict(float %a) #0 {
 ; CHECK-LABEL: @fold_fsub_nsz_nnan_x_n0_ebstrict(
 ; CHECK-NEXT:    [[SUB:%.*]] = call nnan nsz float @llvm.experimental.constrained.fsub.f32(float [[A:%.*]], float -0.000000e+00, metadata !"round.tonearest", metadata !"fpexcept.strict") #[[ATTR0]]
 ; CHECK-NEXT:    ret float [[A]]
 ;
   %sub = call nsz nnan float @llvm.experimental.constrained.fsub.f32(float %a, float -0.0, metadata !"round.tonearest", metadata !"fpexcept.strict") #0
   ret float %sub
 }

 ; CHECK-NEXT:    [[SUB:%.*]] = call float @llvm.experimental.constrained.fsub.f32(float [[ABSA]], float -0.000000e+00, metadata !"round.tonearest", metadata !"fpexcept.strict") #[[ATTR0]]
 ; CHECK-NEXT:    ret float [[SUB]]
 ;
   %absa = call float @llvm.fabs.f32(float %a)
   %sub = call float @llvm.experimental.constrained.fsub.f32(float %absa, float -0.0, metadata !"round.tonearest", metadata !"fpexcept.strict") #0
   ret float %sub
 }
 
-; TODO: The instruction is expected to remain, but the result isn't used.
+; The instruction is expected to remain, but the result isn't used.
 define float @fold_fsub_fabs_nnan_x_n0_ebstrict(float %a) #0 {
 ; CHECK-LABEL: @fold_fsub_fabs_nnan_x_n0_ebstrict(
 ; CHECK-NEXT:    [[ABSA:%.*]] = call float @llvm.fabs.f32(float [[A:%.*]])
 ; CHECK-NEXT:    [[SUB:%.*]] = call nnan float @llvm.experimental.constrained.fsub.f32(float [[ABSA]], float -0.000000e+00, metadata !"round.tonearest", metadata !"fpexcept.strict") #[[ATTR0]]
 ; CHECK-NEXT:    ret float [[ABSA]]
 ;
   %absa = call float @llvm.fabs.f32(float %a)
   %sub = call nnan float @llvm.experimental.constrained.fsub.f32(float %absa, float -0.0, metadata !"round.tonearest", metadata !"fpexcept.strict") #0

 ; CHECK-NEXT:    [[RET:%.*]] = call float @llvm.experimental.constrained.fsub.f32(float -0.000000e+00, float [[NEGA]], metadata !"round.tonearest", metadata !"fpexcept.strict") #[[ATTR0]]
 ; CHECK-NEXT:    ret float [[RET]]
 ;
   %nega = fneg float %a
   %ret = call float @llvm.experimental.constrained.fsub.f32(float -0.0, float %nega, metadata !"round.tonearest", metadata !"fpexcept.strict") #0
   ret float %ret
 }
 
-; NOTE: The instruction is expected to remain, but the result isn't used.
+; 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 [[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

 ; CHECK-NEXT:    [[RET:%.*]] = call nsz float @llvm.experimental.constrained.fsub.f32(float 0.000000e+00, float [[NEGA]], metadata !"round.tonearest", metadata !"fpexcept.maytrap") #[[ATTR0]]
 ; CHECK-NEXT:    ret float [[RET]]
 ;
   %nega = fneg float %a
   %ret = call nsz float @llvm.experimental.constrained.fsub.f32(float 0.0, float %nega, metadata !"round.tonearest", metadata !"fpexcept.maytrap") #0
   ret float %ret
 }
 
-; TODO: This will fold if we allow non-default floating point environments.
 define float @fsub_fneg_nsz_nnan_p0_fnX_ebmaytrap(float %a) #0 {
 ; CHECK-LABEL: @fsub_fneg_nsz_nnan_p0_fnX_ebmaytrap(
-; CHECK-NEXT:    [[NEGA:%.*]] = fneg float [[A:%.*]]
-; CHECK-NEXT:    [[RET:%.*]] = call nnan nsz 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 nsz float @llvm.experimental.constrained.fsub.f32(float 0.0, float %nega, metadata !"round.tonearest", metadata !"fpexcept.maytrap") #0
   ret float %ret
 }
 
 ; Missing nnan: must not fire.
 define float @fsub_fneg_nsz_p0_fnX_ebstrict(float %a) #0 {
 ; CHECK-LABEL: @fsub_fneg_nsz_p0_fnX_ebstrict(
 ; CHECK-NEXT:    [[NEGA:%.*]] = fneg float [[A:%.*]]
 ; CHECK-NEXT:    [[RET:%.*]] = call nsz float @llvm.experimental.constrained.fsub.f32(float 0.000000e+00, float [[NEGA]], metadata !"round.tonearest", metadata !"fpexcept.strict") #[[ATTR0]]
 ; CHECK-NEXT:    ret float [[RET]]
 ;
   %nega = fneg float %a
   %ret = call nsz float @llvm.experimental.constrained.fsub.f32(float 0.0, float %nega, metadata !"round.tonearest", metadata !"fpexcept.strict") #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.
+; The instruction is expected to remain, but the result isn't used.
 define float @fsub_fneg_nnan_nsz_p0_fnX_ebstrict(float %a) #0 {
 ; CHECK-LABEL: @fsub_fneg_nnan_nsz_p0_fnX_ebstrict(
 ; CHECK-NEXT:    [[NEGA:%.*]] = fneg float [[A:%.*]]
 ; CHECK-NEXT:    [[RET:%.*]] = call nnan nsz 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 nsz float @llvm.experimental.constrained.fsub.f32(float 0.0, float %nega, metadata !"round.tonearest", metadata !"fpexcept.strict") #0
   ret float %ret
 }
 
 ;
 ; fsub 0.0, (fsub 0.0, X) ==> X if signed zeros are ignored.

 ; CHECK-NEXT:    [[RET:%.*]] = call float @llvm.experimental.constrained.fsub.f32(float [[A:%.*]], float [[A]], metadata !"round.tonearest", metadata !"fpexcept.strict") #[[ATTR0]]
 ; CHECK-NEXT:    ret float [[RET]]
 ;
   %ret = call float @llvm.experimental.constrained.fsub.f32(float %a, float %a, metadata !"round.tonearest", metadata !"fpexcept.strict") #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.
+; The instruction is expected to remain, but the result isn't used.
 define float @fsub_nnan_x_x_ebstrict(float %a) #0 {
 ; CHECK-LABEL: @fsub_nnan_x_x_ebstrict(
 ; CHECK-NEXT:    [[RET:%.*]] = call nnan float @llvm.experimental.constrained.fsub.f32(float [[A:%.*]], float [[A]], metadata !"round.tonearest", metadata !"fpexcept.strict") #[[ATTR0]]
 ; CHECK-NEXT:    ret float [[RET]]
 ;
   %ret = call nnan float @llvm.experimental.constrained.fsub.f32(float %a, float %a, metadata !"round.tonearest", metadata !"fpexcept.strict") #0
   ret float %ret
 }