[PATCH] D111450: [FPEnv][InstSimplify] Fold fadd X, 0 ==> X, when we know X is not -0

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

kpn created this revision.
kpn added reviewers: sepavloff, spatel, lebedev.ri, nlopes.
kpn requested review of this revision.
Herald added a project: LLVM.
Herald added a subscriber: llvm-commits.

Currently the fadd optimizations in InstSimplify don't know how to do this NoSignedZeros "X + 0.0 ==> X" fold when using the constrained intrinsics. This adds the support.

This review is derived from D106362 <https://reviews.llvm.org/D106362> with some improvements from D107285 <https://reviews.llvm.org/D107285> and is a follow-on to D111085 <https://reviews.llvm.org/D111085>.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D111450

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


Index: llvm/test/Transforms/InstSimplify/strictfp-fadd.ll
===================================================================
--- llvm/test/Transforms/InstSimplify/strictfp-fadd.ll
+++ llvm/test/Transforms/InstSimplify/strictfp-fadd.ll
@@ -247,8 +247,7 @@
 
 define float @fold_fadd_nnan_nsz_x_0_ebmaytrap(float %a) #0 {
 ; CHECK-LABEL: @fold_fadd_nnan_nsz_x_0_ebmaytrap(
-; CHECK-NEXT:    [[ADD:%.*]] = call nnan nsz float @llvm.experimental.constrained.fadd.f32(float [[A:%.*]], float 0.000000e+00, metadata !"round.tonearest", metadata !"fpexcept.maytrap") #[[ATTR0]]
-; CHECK-NEXT:    ret float [[ADD]]
+; CHECK-NEXT:    ret float [[A:%.*]]
 ;
   %add = call nnan nsz float @llvm.experimental.constrained.fadd.f32(float %a, float 0.0, metadata !"round.tonearest", metadata !"fpexcept.maytrap") #0
   ret float %add
@@ -256,8 +255,7 @@
 
 define <2 x float> @fold_fadd_vec_nnan_nsz_x_0_ebmaytrap(<2 x float> %a) #0 {
 ; CHECK-LABEL: @fold_fadd_vec_nnan_nsz_x_0_ebmaytrap(
-; CHECK-NEXT:    [[ADD:%.*]] = call nnan nsz <2 x float> @llvm.experimental.constrained.fadd.v2f32(<2 x float> [[A:%.*]], <2 x float> zeroinitializer, metadata !"round.tonearest", metadata !"fpexcept.maytrap") #[[ATTR0]]
-; CHECK-NEXT:    ret <2 x float> [[ADD]]
+; CHECK-NEXT:    ret <2 x float> [[A:%.*]]
 ;
   %add = call nnan nsz <2 x float> @llvm.experimental.constrained.fadd.v2f32(<2 x float> %a, <2 x float> zeroinitializer, metadata !"round.tonearest", metadata !"fpexcept.maytrap") #0
   ret <2 x float> %add
@@ -284,7 +282,7 @@
 define float @fold_fadd_nsz_nnan_x_0_ebstrict(float %a) #0 {
 ; CHECK-LABEL: @fold_fadd_nsz_nnan_x_0_ebstrict(
 ; CHECK-NEXT:    [[ADD:%.*]] = call nnan nsz float @llvm.experimental.constrained.fadd.f32(float [[A:%.*]], float 0.000000e+00, metadata !"round.tonearest", metadata !"fpexcept.strict") #[[ATTR0]]
-; CHECK-NEXT:    ret float [[ADD]]
+; CHECK-NEXT:    ret float [[A]]
 ;
   %add = call nsz nnan float @llvm.experimental.constrained.fadd.f32(float %a, float 0.0, metadata !"round.tonearest", metadata !"fpexcept.strict") #0
   ret float %add
@@ -293,7 +291,7 @@
 define <2 x float> @fold_fadd_vec_nsz_nnan_x_0_ebstrict(<2 x float> %a) #0 {
 ; CHECK-LABEL: @fold_fadd_vec_nsz_nnan_x_0_ebstrict(
 ; CHECK-NEXT:    [[ADD:%.*]] = call nnan nsz <2 x float> @llvm.experimental.constrained.fadd.v2f32(<2 x float> [[A:%.*]], <2 x float> zeroinitializer, metadata !"round.tonearest", metadata !"fpexcept.strict") #[[ATTR0]]
-; CHECK-NEXT:    ret <2 x float> [[ADD]]
+; CHECK-NEXT:    ret <2 x float> [[A]]
 ;
   %add = call nsz nnan <2 x float> @llvm.experimental.constrained.fadd.v2f32(<2 x float> %a, <2 x float> zeroinitializer, metadata !"round.tonearest", metadata !"fpexcept.strict") #0
   ret <2 x float> %add
Index: llvm/lib/Analysis/InstructionSimplify.cpp
===================================================================
--- llvm/lib/Analysis/InstructionSimplify.cpp
+++ llvm/lib/Analysis/InstructionSimplify.cpp
@@ -4978,14 +4978,15 @@
     if (match(Op1, m_NegZeroFP()))
       return Op0;
 
+  // fadd X, 0 ==> X, when we know X is not -0
+  if (canIgnoreSNaN(ExBehavior, FMF))
+    if (match(Op1, m_PosZeroFP()) &&
+        (FMF.noSignedZeros() || CannotBeNegativeZero(Op0, Q.TLI)))
+      return Op0;
+
   if (!isDefaultFPEnvironment(ExBehavior, Rounding))
     return nullptr;
 
-  // fadd X, 0 ==> X, when we know X is not -0
-  if (match(Op1, m_PosZeroFP()) &&
-      (FMF.noSignedZeros() || CannotBeNegativeZero(Op0, Q.TLI)))
-    return Op0;
-
   // With nnan: -X + X --> 0.0 (and commuted variant)
   // We don't have to explicitly exclude infinities (ninf): INF + -INF == NaN.
   // Negative zeros are allowed because we always end up with positive zero:


-------------- next part --------------
A non-text attachment was scrubbed...
Name: D111450.378317.patch
Type: text/x-patch
Size: 3697 bytes
Desc: not available
URL: <http://lists.llvm.org/pipermail/llvm-commits/attachments/20211008/3cc4b06d/attachment.bin>