[PATCH] D119746: [FPEnv][InstSimplify] Fold fsub X, -0 ==> X, when we know X is not -0
Kevin P. Neal via Phabricator via llvm-commits
llvm-commits at lists.llvm.org
Mon Feb 14 10:58:31 PST 2022
kpn created this revision.
kpn added reviewers: sepavloff, spatel, nlopes, lebedev.ri.
Herald added a subscriber: hiraditya.
kpn requested review of this revision.
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Herald added a subscriber: llvm-commits.
Currently the fsub optimizations in InstSimplify don't know how to fold X - -0.0 to X when we know X is not zero and the constrained intrinsics are used. 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/D119746
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
@@ -127,11 +127,9 @@
ret float %sub
}
-; TODO: This will fold if we allow non-default floating point environments.
define float @fold_fsub_nnan_nsz_x_n0_ebmaytrap(float %a) #0 {
; CHECK-LABEL: @fold_fsub_nnan_nsz_x_n0_ebmaytrap(
-; CHECK-NEXT: [[SUB:%.*]] = call nnan nsz float @llvm.experimental.constrained.fsub.f32(float [[A:%.*]], float -0.000000e+00, metadata !"round.tonearest", metadata !"fpexcept.maytrap") #[[ATTR0]]
-; CHECK-NEXT: ret float [[SUB]]
+; CHECK-NEXT: ret float [[A:%.*]]
;
%sub = call nnan nsz float @llvm.experimental.constrained.fsub.f32(float %a, float -0.0, metadata !"round.tonearest", metadata !"fpexcept.maytrap") #0
ret float %sub
@@ -147,12 +145,11 @@
ret float %sub
}
-; 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 @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 [[SUB]]
+; 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
@@ -185,12 +182,10 @@
ret float %sub
}
-; TODO: This will fold if we allow non-default floating point environments.
define float @fold_fsub_fabs_nnan_x_n0_ebmaytrap(float %a) #0 {
; CHECK-LABEL: @fold_fsub_fabs_nnan_x_n0_ebmaytrap(
; 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.maytrap") #[[ATTR0]]
-; CHECK-NEXT: ret float [[SUB]]
+; 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.maytrap") #0
@@ -209,13 +204,12 @@
ret float %sub
}
-; 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 @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 [[SUB]]
+; 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
Index: llvm/lib/Analysis/InstructionSimplify.cpp
===================================================================
--- llvm/lib/Analysis/InstructionSimplify.cpp
+++ llvm/lib/Analysis/InstructionSimplify.cpp
@@ -5143,14 +5143,15 @@
if (match(Op1, m_PosZeroFP()))
return Op0;
+ // fsub X, -0 ==> X, when we know X is not -0
+ if (canIgnoreSNaN(ExBehavior, FMF))
+ if (match(Op1, m_NegZeroFP()) &&
+ (FMF.noSignedZeros() || CannotBeNegativeZero(Op0, Q.TLI)))
+ return Op0;
+
if (!isDefaultFPEnvironment(ExBehavior, Rounding))
return nullptr;
- // fsub X, -0 ==> X, when we know X is not -0
- if (match(Op1, m_NegZeroFP()) &&
- (FMF.noSignedZeros() || CannotBeNegativeZero(Op0, Q.TLI)))
- return Op0;
-
// fsub -0.0, (fsub -0.0, X) ==> X
// fsub -0.0, (fneg X) ==> X
Value *X;
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