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

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.

Differential Revision: https://reviews.llvm.org/D131607

diff --git a/llvm/lib/Analysis/InstructionSimplify.cpp b/llvm/lib/Analysis/InstructionSimplify.cpp
index 62d4400..bff9a40 100644 (file)
--- a/llvm/lib/Analysis/InstructionSimplify.cpp
+++ b/llvm/lib/Analysis/InstructionSimplify.cpp
@@ -5200,15 +5200,16 @@ simplifyFSubInst(Value *Op0, Value *Op1, FastMathFlags 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 (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 (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)

diff --git a/llvm/test/Transforms/InstSimplify/strictfp-fsub.ll b/llvm/test/Transforms/InstSimplify/strictfp-fsub.ll
index 801b2a1..74cf72e 100644 (file)
--- a/llvm/test/Transforms/InstSimplify/strictfp-fsub.ll
+++ b/llvm/test/Transforms/InstSimplify/strictfp-fsub.ll
@@ -45,7 +45,7 @@ define float @fsub_x_p0_ebstrict(float %a) #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]]
@@ -145,7 +145,7 @@ define float @fold_fsub_nsz_x_n0_ebstrict(float %a) #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]]
@@ -204,7 +204,7 @@ define float @fold_fsub_fabs_x_n0_ebstrict(float %a) #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:%.*]])
@@ -272,7 +272,7 @@ define float @fsub_fneg_n0_fnX_ebstrict(float %a) #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:%.*]]
@@ -373,12 +373,9 @@ define float @fsub_fneg_nsz_p0_fnX_ebmaytrap(float %a) #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
@@ -397,13 +394,12 @@ define float @fsub_fneg_nsz_p0_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.
+; 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
@@ -527,7 +523,7 @@ define float @fsub_x_x_ebstrict(float %a) #0 {
 }
 
 ; 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]]