[llvm] [InstCombine] Fix FMF propagation in `foldSelectWithFCmpToFabs` (PR #121580)
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llvm-commits at lists.llvm.org
Fri Jan 3 08:22:30 PST 2025
llvmbot wrote:
<!--LLVM PR SUMMARY COMMENT-->
@llvm/pr-subscribers-llvm-transforms
Author: Yingwei Zheng (dtcxzyw)
<details>
<summary>Changes</summary>
Consider the following pattern:
```
%cmp = fcmp <pred> double %x, 0.000000e+00
%negX = fneg <fmf> double %x
%sel = select i1 %cmp, double %x, double %negX
```
We cannot propagate ninf from fneg to select since `%negX` may not be chosen. Similarly, we cannot propagate nnan unless `%negX` is guaranteed to be selected when `%x` is NaN.
This patch also propagates nnan/ninf from fcmp to avoid regression in `PhaseOrdering/generate-fabs.ll`.
Alive2: https://alive2.llvm.org/ce/z/t6U-tA
Closes https://github.com/llvm/llvm-project/issues/121430.
---
Full diff: https://github.com/llvm/llvm-project/pull/121580.diff
3 Files Affected:
- (modified) llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp (+9-2)
- (modified) llvm/test/Transforms/InstCombine/fabs.ll (+20-20)
- (modified) llvm/test/Transforms/InstCombine/fneg-fabs.ll (+9-8)
``````````diff
diff --git a/llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp b/llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp
index e7a8e947705f8d..3a1536bd1e8de3 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp
@@ -2926,10 +2926,10 @@ static Instruction *foldSelectWithFCmpToFabs(SelectInst &SI,
if (!match(TrueVal, m_FNeg(m_Specific(X))))
return nullptr;
- // Forward-propagate nnan and ninf from the fneg to the select.
+ // Forward-propagate nnan and ninf from the fcmp to the select.
// If all inputs are not those values, then the select is not either.
// Note: nsz is defined differently, so it may not be correct to propagate.
- FastMathFlags FMF = cast<FPMathOperator>(TrueVal)->getFastMathFlags();
+ FastMathFlags FMF = cast<FPMathOperator>(CondVal)->getFastMathFlags();
if (FMF.noNaNs() && !SI.hasNoNaNs()) {
SI.setHasNoNaNs(true);
ChangedFMF = true;
@@ -2938,6 +2938,13 @@ static Instruction *foldSelectWithFCmpToFabs(SelectInst &SI,
SI.setHasNoInfs(true);
ChangedFMF = true;
}
+ // Forward-propagate nnan from the fneg to the select.
+ // The nnan flag can be propagated iff fneg is selected when X is NaN.
+ if (!SI.hasNoNaNs() && cast<FPMathOperator>(TrueVal)->hasNoNaNs() &&
+ (Swap ? FCmpInst::isOrdered(Pred) : FCmpInst::isUnordered(Pred))) {
+ SI.setHasNoNaNs(true);
+ ChangedFMF = true;
+ }
// With nsz, when 'Swap' is false:
// fold (X < +/-0.0) ? -X : X or (X <= +/-0.0) ? -X : X to fabs(X)
diff --git a/llvm/test/Transforms/InstCombine/fabs.ll b/llvm/test/Transforms/InstCombine/fabs.ll
index cccf0f4457b6ab..7b9a672f188cab 100644
--- a/llvm/test/Transforms/InstCombine/fabs.ll
+++ b/llvm/test/Transforms/InstCombine/fabs.ll
@@ -484,7 +484,7 @@ define double @select_fcmp_nnan_nsz_olt_zero(double %x) {
; CHECK-LABEL: @select_fcmp_nnan_nsz_olt_zero(
; CHECK-NEXT: [[LTZERO:%.*]] = fcmp olt double [[X:%.*]], 0.000000e+00
; CHECK-NEXT: [[NEGX:%.*]] = fneg nnan nsz double [[X]]
-; CHECK-NEXT: [[FABS:%.*]] = select nnan i1 [[LTZERO]], double [[NEGX]], double [[X]]
+; CHECK-NEXT: [[FABS:%.*]] = select i1 [[LTZERO]], double [[NEGX]], double [[X]]
; CHECK-NEXT: ret double [[FABS]]
;
%ltzero = fcmp olt double %x, 0.0
@@ -523,7 +523,7 @@ define double @select_fcmp_nnan_nsz_olt_zero_unary_fneg(double %x) {
; CHECK-LABEL: @select_fcmp_nnan_nsz_olt_zero_unary_fneg(
; CHECK-NEXT: [[LTZERO:%.*]] = fcmp olt double [[X:%.*]], 0.000000e+00
; CHECK-NEXT: [[NEGX:%.*]] = fneg nnan nsz double [[X]]
-; CHECK-NEXT: [[FABS:%.*]] = select nnan i1 [[LTZERO]], double [[NEGX]], double [[X]]
+; CHECK-NEXT: [[FABS:%.*]] = select i1 [[LTZERO]], double [[NEGX]], double [[X]]
; CHECK-NEXT: ret double [[FABS]]
;
%ltzero = fcmp olt double %x, 0.0
@@ -553,7 +553,7 @@ define float @select_fcmp_nnan_nsz_olt_negzero(float %x) {
; CHECK-LABEL: @select_fcmp_nnan_nsz_olt_negzero(
; CHECK-NEXT: [[LTZERO:%.*]] = fcmp olt float [[X:%.*]], 0.000000e+00
; CHECK-NEXT: [[NEGX:%.*]] = fneg nnan ninf nsz float [[X]]
-; CHECK-NEXT: [[FABS:%.*]] = select nnan ninf i1 [[LTZERO]], float [[NEGX]], float [[X]]
+; CHECK-NEXT: [[FABS:%.*]] = select i1 [[LTZERO]], float [[NEGX]], float [[X]]
; CHECK-NEXT: ret float [[FABS]]
;
%ltzero = fcmp olt float %x, -0.0
@@ -579,7 +579,7 @@ define float @select_fcmp_nnan_nsz_ult_negzero(float %x) {
; CHECK-LABEL: @select_fcmp_nnan_nsz_ult_negzero(
; CHECK-NEXT: [[LTZERO:%.*]] = fcmp ult float [[X:%.*]], 0.000000e+00
; CHECK-NEXT: [[NEGX:%.*]] = fneg nnan ninf nsz float [[X]]
-; CHECK-NEXT: [[FABS:%.*]] = select nnan ninf i1 [[LTZERO]], float [[NEGX]], float [[X]]
+; CHECK-NEXT: [[FABS:%.*]] = select nnan i1 [[LTZERO]], float [[NEGX]], float [[X]]
; CHECK-NEXT: ret float [[FABS]]
;
%ltzero = fcmp ult float %x, -0.0
@@ -592,7 +592,7 @@ define float @select_fcmp_nnan_nsz_olt_negzero_unary_fneg(float %x) {
; CHECK-LABEL: @select_fcmp_nnan_nsz_olt_negzero_unary_fneg(
; CHECK-NEXT: [[LTZERO:%.*]] = fcmp olt float [[X:%.*]], 0.000000e+00
; CHECK-NEXT: [[NEGX:%.*]] = fneg nnan ninf nsz float [[X]]
-; CHECK-NEXT: [[FABS:%.*]] = select nnan ninf i1 [[LTZERO]], float [[NEGX]], float [[X]]
+; CHECK-NEXT: [[FABS:%.*]] = select i1 [[LTZERO]], float [[NEGX]], float [[X]]
; CHECK-NEXT: ret float [[FABS]]
;
%ltzero = fcmp olt float %x, -0.0
@@ -607,7 +607,7 @@ define float @select_fcmp_nnan_nsz_ult_negzero_unary_fneg(float %x) {
; CHECK-LABEL: @select_fcmp_nnan_nsz_ult_negzero_unary_fneg(
; CHECK-NEXT: [[LTZERO:%.*]] = fcmp ult float [[X:%.*]], 0.000000e+00
; CHECK-NEXT: [[NEGX:%.*]] = fneg nnan ninf nsz float [[X]]
-; CHECK-NEXT: [[FABS:%.*]] = select nnan ninf i1 [[LTZERO]], float [[NEGX]], float [[X]]
+; CHECK-NEXT: [[FABS:%.*]] = select nnan i1 [[LTZERO]], float [[NEGX]], float [[X]]
; CHECK-NEXT: ret float [[FABS]]
;
%ltzero = fcmp ult float %x, -0.0
@@ -622,7 +622,7 @@ define double @select_fcmp_nnan_nsz_ole_zero(double %x) {
; CHECK-LABEL: @select_fcmp_nnan_nsz_ole_zero(
; CHECK-NEXT: [[LEZERO:%.*]] = fcmp ole double [[X:%.*]], 0.000000e+00
; CHECK-NEXT: [[NEGX:%.*]] = fneg fast double [[X]]
-; CHECK-NEXT: [[FABS:%.*]] = select nnan ninf i1 [[LEZERO]], double [[NEGX]], double [[X]]
+; CHECK-NEXT: [[FABS:%.*]] = select i1 [[LEZERO]], double [[NEGX]], double [[X]]
; CHECK-NEXT: ret double [[FABS]]
;
%lezero = fcmp ole double %x, 0.0
@@ -648,7 +648,7 @@ define double @select_fcmp_nnan_nsz_ule_zero(double %x) {
; CHECK-LABEL: @select_fcmp_nnan_nsz_ule_zero(
; CHECK-NEXT: [[LEZERO:%.*]] = fcmp ule double [[X:%.*]], 0.000000e+00
; CHECK-NEXT: [[NEGX:%.*]] = fneg fast double [[X]]
-; CHECK-NEXT: [[FABS:%.*]] = select nnan ninf i1 [[LEZERO]], double [[NEGX]], double [[X]]
+; CHECK-NEXT: [[FABS:%.*]] = select nnan i1 [[LEZERO]], double [[NEGX]], double [[X]]
; CHECK-NEXT: ret double [[FABS]]
;
%lezero = fcmp ule double %x, 0.0
@@ -661,7 +661,7 @@ define double @select_fcmp_nnan_nsz_ole_zero_unary_fneg(double %x) {
; CHECK-LABEL: @select_fcmp_nnan_nsz_ole_zero_unary_fneg(
; CHECK-NEXT: [[LEZERO:%.*]] = fcmp ole double [[X:%.*]], 0.000000e+00
; CHECK-NEXT: [[NEGX:%.*]] = fneg fast double [[X]]
-; CHECK-NEXT: [[FABS:%.*]] = select nnan ninf i1 [[LEZERO]], double [[NEGX]], double [[X]]
+; CHECK-NEXT: [[FABS:%.*]] = select i1 [[LEZERO]], double [[NEGX]], double [[X]]
; CHECK-NEXT: ret double [[FABS]]
;
%lezero = fcmp ole double %x, 0.0
@@ -676,7 +676,7 @@ define double @select_fcmp_nnan_nsz_ule_zero_unary_fneg(double %x) {
; CHECK-LABEL: @select_fcmp_nnan_nsz_ule_zero_unary_fneg(
; CHECK-NEXT: [[LEZERO:%.*]] = fcmp ule double [[X:%.*]], 0.000000e+00
; CHECK-NEXT: [[NEGX:%.*]] = fneg fast double [[X]]
-; CHECK-NEXT: [[FABS:%.*]] = select nnan ninf i1 [[LEZERO]], double [[NEGX]], double [[X]]
+; CHECK-NEXT: [[FABS:%.*]] = select nnan i1 [[LEZERO]], double [[NEGX]], double [[X]]
; CHECK-NEXT: ret double [[FABS]]
;
%lezero = fcmp ule double %x, 0.0
@@ -691,7 +691,7 @@ define float @select_fcmp_nnan_nsz_ole_negzero(float %x) {
; CHECK-LABEL: @select_fcmp_nnan_nsz_ole_negzero(
; CHECK-NEXT: [[LEZERO:%.*]] = fcmp ole float [[X:%.*]], 0.000000e+00
; CHECK-NEXT: [[NEGX:%.*]] = fneg nnan nsz float [[X]]
-; CHECK-NEXT: [[FABS:%.*]] = select nnan i1 [[LEZERO]], float [[NEGX]], float [[X]]
+; CHECK-NEXT: [[FABS:%.*]] = select i1 [[LEZERO]], float [[NEGX]], float [[X]]
; CHECK-NEXT: ret float [[FABS]]
;
%lezero = fcmp ole float %x, -0.0
@@ -730,7 +730,7 @@ define float @select_fcmp_nnan_nsz_ole_negzero_unary_fneg(float %x) {
; CHECK-LABEL: @select_fcmp_nnan_nsz_ole_negzero_unary_fneg(
; CHECK-NEXT: [[LEZERO:%.*]] = fcmp ole float [[X:%.*]], 0.000000e+00
; CHECK-NEXT: [[NEGX:%.*]] = fneg nnan nsz float [[X]]
-; CHECK-NEXT: [[FABS:%.*]] = select nnan i1 [[LEZERO]], float [[NEGX]], float [[X]]
+; CHECK-NEXT: [[FABS:%.*]] = select i1 [[LEZERO]], float [[NEGX]], float [[X]]
; CHECK-NEXT: ret float [[FABS]]
;
%lezero = fcmp ole float %x, -0.0
@@ -802,7 +802,7 @@ define <2 x float> @select_fcmp_nnan_nsz_ugt_zero(<2 x float> %x) {
; CHECK-LABEL: @select_fcmp_nnan_nsz_ugt_zero(
; CHECK-NEXT: [[GTZERO:%.*]] = fcmp ugt <2 x float> [[X:%.*]], zeroinitializer
; CHECK-NEXT: [[NEGX:%.*]] = fneg nnan nsz arcp <2 x float> [[X]]
-; CHECK-NEXT: [[FABS:%.*]] = select nnan <2 x i1> [[GTZERO]], <2 x float> [[X]], <2 x float> [[NEGX]]
+; CHECK-NEXT: [[FABS:%.*]] = select <2 x i1> [[GTZERO]], <2 x float> [[X]], <2 x float> [[NEGX]]
; CHECK-NEXT: ret <2 x float> [[FABS]]
;
%gtzero = fcmp ugt <2 x float> %x, zeroinitializer
@@ -830,7 +830,7 @@ define <2 x float> @select_fcmp_nnan_nsz_ugt_zero_unary_fneg(<2 x float> %x) {
; CHECK-LABEL: @select_fcmp_nnan_nsz_ugt_zero_unary_fneg(
; CHECK-NEXT: [[GTZERO:%.*]] = fcmp ugt <2 x float> [[X:%.*]], zeroinitializer
; CHECK-NEXT: [[NEGX:%.*]] = fneg nnan nsz arcp <2 x float> [[X]]
-; CHECK-NEXT: [[FABS:%.*]] = select nnan <2 x i1> [[GTZERO]], <2 x float> [[X]], <2 x float> [[NEGX]]
+; CHECK-NEXT: [[FABS:%.*]] = select <2 x i1> [[GTZERO]], <2 x float> [[X]], <2 x float> [[NEGX]]
; CHECK-NEXT: ret <2 x float> [[FABS]]
;
%gtzero = fcmp ugt <2 x float> %x, zeroinitializer
@@ -845,7 +845,7 @@ define half @select_fcmp_nnan_nsz_ogt_negzero(half %x) {
; CHECK-LABEL: @select_fcmp_nnan_nsz_ogt_negzero(
; CHECK-NEXT: [[GTZERO:%.*]] = fcmp ogt half [[X:%.*]], 0xH0000
; CHECK-NEXT: [[NEGX:%.*]] = fneg fast half [[X]]
-; CHECK-NEXT: [[FABS:%.*]] = select nnan ninf i1 [[GTZERO]], half [[X]], half [[NEGX]]
+; CHECK-NEXT: [[FABS:%.*]] = select nnan i1 [[GTZERO]], half [[X]], half [[NEGX]]
; CHECK-NEXT: ret half [[FABS]]
;
%gtzero = fcmp ogt half %x, -0.0
@@ -860,7 +860,7 @@ define half @select_fcmp_nnan_nsz_ugt_negzero(half %x) {
; CHECK-LABEL: @select_fcmp_nnan_nsz_ugt_negzero(
; CHECK-NEXT: [[GTZERO:%.*]] = fcmp ugt half [[X:%.*]], 0xH0000
; CHECK-NEXT: [[NEGX:%.*]] = fneg fast half [[X]]
-; CHECK-NEXT: [[FABS:%.*]] = select nnan ninf i1 [[GTZERO]], half [[X]], half [[NEGX]]
+; CHECK-NEXT: [[FABS:%.*]] = select i1 [[GTZERO]], half [[X]], half [[NEGX]]
; CHECK-NEXT: ret half [[FABS]]
;
%gtzero = fcmp ugt half %x, -0.0
@@ -890,7 +890,7 @@ define <2 x double> @select_fcmp_nnan_nsz_uge_zero(<2 x double> %x) {
; CHECK-LABEL: @select_fcmp_nnan_nsz_uge_zero(
; CHECK-NEXT: [[GEZERO:%.*]] = fcmp uge <2 x double> [[X:%.*]], zeroinitializer
; CHECK-NEXT: [[NEGX:%.*]] = fneg reassoc nnan nsz <2 x double> [[X]]
-; CHECK-NEXT: [[FABS:%.*]] = select nnan <2 x i1> [[GEZERO]], <2 x double> [[X]], <2 x double> [[NEGX]]
+; CHECK-NEXT: [[FABS:%.*]] = select <2 x i1> [[GEZERO]], <2 x double> [[X]], <2 x double> [[NEGX]]
; CHECK-NEXT: ret <2 x double> [[FABS]]
;
%gezero = fcmp uge <2 x double> %x, zeroinitializer
@@ -918,7 +918,7 @@ define <2 x double> @select_fcmp_nnan_nsz_uge_zero_unary_fneg(<2 x double> %x) {
; CHECK-LABEL: @select_fcmp_nnan_nsz_uge_zero_unary_fneg(
; CHECK-NEXT: [[GEZERO:%.*]] = fcmp uge <2 x double> [[X:%.*]], zeroinitializer
; CHECK-NEXT: [[NEGX:%.*]] = fneg reassoc nnan nsz <2 x double> [[X]]
-; CHECK-NEXT: [[FABS:%.*]] = select nnan <2 x i1> [[GEZERO]], <2 x double> [[X]], <2 x double> [[NEGX]]
+; CHECK-NEXT: [[FABS:%.*]] = select <2 x i1> [[GEZERO]], <2 x double> [[X]], <2 x double> [[NEGX]]
; CHECK-NEXT: ret <2 x double> [[FABS]]
;
%gezero = fcmp uge <2 x double> %x, zeroinitializer
@@ -948,7 +948,7 @@ define half @select_fcmp_nnan_nsz_uge_negzero(half %x) {
; CHECK-LABEL: @select_fcmp_nnan_nsz_uge_negzero(
; CHECK-NEXT: [[GEZERO:%.*]] = fcmp uge half [[X:%.*]], 0xH0000
; CHECK-NEXT: [[NEGX:%.*]] = fneg nnan nsz half [[X]]
-; CHECK-NEXT: [[FABS:%.*]] = select nnan i1 [[GEZERO]], half [[X]], half [[NEGX]]
+; CHECK-NEXT: [[FABS:%.*]] = select i1 [[GEZERO]], half [[X]], half [[NEGX]]
; CHECK-NEXT: ret half [[FABS]]
;
%gezero = fcmp uge half %x, -0.0
@@ -976,7 +976,7 @@ define half @select_fcmp_nnan_nsz_uge_negzero_unary_fneg(half %x) {
; CHECK-LABEL: @select_fcmp_nnan_nsz_uge_negzero_unary_fneg(
; CHECK-NEXT: [[GEZERO:%.*]] = fcmp uge half [[X:%.*]], 0xH0000
; CHECK-NEXT: [[NEGX:%.*]] = fneg nnan nsz half [[X]]
-; CHECK-NEXT: [[FABS:%.*]] = select nnan i1 [[GEZERO]], half [[X]], half [[NEGX]]
+; CHECK-NEXT: [[FABS:%.*]] = select i1 [[GEZERO]], half [[X]], half [[NEGX]]
; CHECK-NEXT: ret half [[FABS]]
;
%gezero = fcmp uge half %x, -0.0
diff --git a/llvm/test/Transforms/InstCombine/fneg-fabs.ll b/llvm/test/Transforms/InstCombine/fneg-fabs.ll
index fdcdfd123eefa4..c013a2c9f5449c 100644
--- a/llvm/test/Transforms/InstCombine/fneg-fabs.ll
+++ b/llvm/test/Transforms/InstCombine/fneg-fabs.ll
@@ -20,8 +20,8 @@ define double @select_noFMF_nfabs_lt(double %x) {
; One test where the neg has fmfs.
define double @select_nsz_nfabs_lt_fmfProp(double %x) {
; CHECK-LABEL: @select_nsz_nfabs_lt_fmfProp(
-; CHECK-NEXT: [[TMP1:%.*]] = call nnan ninf nsz double @llvm.fabs.f64(double [[X:%.*]])
-; CHECK-NEXT: [[SEL:%.*]] = fneg nnan ninf nsz double [[TMP1]]
+; CHECK-NEXT: [[TMP1:%.*]] = call nnan nsz double @llvm.fabs.f64(double [[X:%.*]])
+; CHECK-NEXT: [[SEL:%.*]] = fneg nnan nsz double [[TMP1]]
; CHECK-NEXT: ret double [[SEL]]
;
%cmp = fcmp olt double %x, 0.000000e+00
@@ -32,8 +32,8 @@ define double @select_nsz_nfabs_lt_fmfProp(double %x) {
define double @select_nsz_nnan_nfabs_lt_fmfProp(double %x) {
; CHECK-LABEL: @select_nsz_nnan_nfabs_lt_fmfProp(
-; CHECK-NEXT: [[TMP1:%.*]] = call nnan ninf nsz double @llvm.fabs.f64(double [[X:%.*]])
-; CHECK-NEXT: [[SEL:%.*]] = fneg nnan ninf nsz double [[TMP1]]
+; CHECK-NEXT: [[TMP1:%.*]] = call nnan nsz double @llvm.fabs.f64(double [[X:%.*]])
+; CHECK-NEXT: [[SEL:%.*]] = fneg nnan nsz double [[TMP1]]
; CHECK-NEXT: ret double [[SEL]]
;
%cmp = fcmp olt double %x, 0.000000e+00
@@ -147,8 +147,9 @@ define double @select_noFMF_nfabs_gt(double %x) {
; One test where the neg has fmfs.
define double @select_nsz_nfabs_gt_fmfProp(double %x) {
; CHECK-LABEL: @select_nsz_nfabs_gt_fmfProp(
-; CHECK-NEXT: [[TMP1:%.*]] = call nnan ninf nsz double @llvm.fabs.f64(double [[X:%.*]])
-; CHECK-NEXT: [[SEL:%.*]] = fneg nnan ninf nsz double [[TMP1]]
+; CHECK-NEXT: [[CMP:%.*]] = fcmp ogt double [[X:%.*]], 0.000000e+00
+; CHECK-NEXT: [[NEGX:%.*]] = fneg fast double [[X]]
+; CHECK-NEXT: [[SEL:%.*]] = select nsz i1 [[CMP]], double [[NEGX]], double [[X]]
; CHECK-NEXT: ret double [[SEL]]
;
%cmp = fcmp ogt double %x, 0.000000e+00
@@ -159,8 +160,8 @@ define double @select_nsz_nfabs_gt_fmfProp(double %x) {
define double @select_nsz_nnan_nfabs_gt_fmfProp(double %x) {
; CHECK-LABEL: @select_nsz_nnan_nfabs_gt_fmfProp(
-; CHECK-NEXT: [[TMP1:%.*]] = call nnan ninf nsz double @llvm.fabs.f64(double [[X:%.*]])
-; CHECK-NEXT: [[SEL:%.*]] = fneg nnan ninf nsz double [[TMP1]]
+; CHECK-NEXT: [[TMP1:%.*]] = call nnan nsz double @llvm.fabs.f64(double [[X:%.*]])
+; CHECK-NEXT: [[SEL:%.*]] = fneg nnan nsz double [[TMP1]]
; CHECK-NEXT: ret double [[SEL]]
;
%cmp = fcmp ogt double %x, 0.000000e+00
``````````
</details>
https://github.com/llvm/llvm-project/pull/121580
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