[InstCombine] Fold fabs over selects #86390

dtcxzyw · 2024-03-23T10:32:30Z

This patch folds fabs over select if it is beneficial. I also tried other interger/fp intrinsics. Only handling fabs shows benefit to some real-world applications.

llvmbot · 2024-03-23T10:33:02Z

@llvm/pr-subscribers-llvm-transforms

Author: Yingwei Zheng (dtcxzyw)

Changes

This patch folds fabs over select if it is beneficial. I also tried other interger/fp intrinsics. Only handling fabs shows benefit to some real-world applications.

Full diff: https://github.com/llvm/llvm-project/pull/86390.diff

4 Files Affected:

(modified) llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp (+1)
(modified) llvm/test/Transforms/InstCombine/fabs.ll (+3-3)
(modified) llvm/test/Transforms/InstCombine/intrinsic-select.ll (+27)
(modified) llvm/test/Transforms/InstCombine/simplify-demanded-fpclass.ll (+12-12)

diff --git a/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp b/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
index 526fe5d080599f..0f1b98cc6ef2af 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
@@ -3432,6 +3432,7 @@ Instruction *InstCombinerImpl::visitCallInst(CallInst &CI) {
   case Intrinsic::uadd_sat:
   case Intrinsic::ssub_sat:
   case Intrinsic::sadd_sat:
+  case Intrinsic::fabs:
     for (Value *Op : II->args())
       if (auto *Sel = dyn_cast<SelectInst>(Op))
         if (Instruction *R = FoldOpIntoSelect(*II, Sel))
diff --git a/llvm/test/Transforms/InstCombine/fabs.ll b/llvm/test/Transforms/InstCombine/fabs.ll
index 7e380c2e4590a0..d8251befca4819 100644
--- a/llvm/test/Transforms/InstCombine/fabs.ll
+++ b/llvm/test/Transforms/InstCombine/fabs.ll
@@ -179,9 +179,9 @@ define float @fabs_select_constant_neg0(i32 %c) {
 define float @fabs_select_var_constant_negative(i32 %c, float %x) {
 ; CHECK-LABEL: @fabs_select_var_constant_negative(
 ; CHECK-NEXT:    [[CMP:%.*]] = icmp eq i32 [[C:%.*]], 0
-; CHECK-NEXT:    [[SELECT:%.*]] = select i1 [[CMP]], float [[X:%.*]], float -1.000000e+00
-; CHECK-NEXT:    [[FABS:%.*]] = call float @llvm.fabs.f32(float [[SELECT]])
-; CHECK-NEXT:    ret float [[FABS]]
+; CHECK-NEXT:    [[FABS:%.*]] = call float @llvm.fabs.f32(float [[SELECT:%.*]])
+; CHECK-NEXT:    [[FABS1:%.*]] = select i1 [[CMP]], float [[FABS]], float 1.000000e+00
+; CHECK-NEXT:    ret float [[FABS1]]
 ;
   %cmp = icmp eq i32 %c, 0
   %select = select i1 %cmp, float %x, float -1.0
diff --git a/llvm/test/Transforms/InstCombine/intrinsic-select.ll b/llvm/test/Transforms/InstCombine/intrinsic-select.ll
index f37226bbd5b09c..bdbfd625442f1b 100644
--- a/llvm/test/Transforms/InstCombine/intrinsic-select.ll
+++ b/llvm/test/Transforms/InstCombine/intrinsic-select.ll
@@ -280,3 +280,30 @@ entry:
   %ret = icmp eq i64 %masked, 0
   ret i1 %ret
 }
+
+define double @test_fabs_select1(double %a) {
+; CHECK-LABEL: @test_fabs_select1(
+; CHECK-NEXT:    [[COND:%.*]] = fcmp uno double [[A:%.*]], 0.000000e+00
+; CHECK-NEXT:    [[SEL1:%.*]] = select i1 [[COND]], double 0x7FF8000000000000, double [[A]]
+; CHECK-NEXT:    ret double [[SEL1]]
+;
+  %cond = fcmp uno double %a, 0.000000e+00
+  %sel1 = select i1 %cond, double 0x7FF8000000000000, double %a
+  %fabs = call double @llvm.fabs.f64(double %sel1)
+  %sel2 = select i1 %cond, double %fabs, double %a
+  ret double %sel2
+}
+
+define double @test_fabs_select2(double %a) {
+; CHECK-LABEL: @test_fabs_select2(
+; CHECK-NEXT:    [[ABS1:%.*]] = call double @llvm.fabs.f64(double [[A:%.*]])
+; CHECK-NEXT:    [[CMP:%.*]] = fcmp oeq double [[ABS1]], 0x7FF0000000000000
+; CHECK-NEXT:    [[ABS2:%.*]] = select i1 [[CMP]], double 0.000000e+00, double [[ABS1]]
+; CHECK-NEXT:    ret double [[ABS2]]
+;
+  %abs1 = call double @llvm.fabs.f64(double %a)
+  %cmp = fcmp oeq double %abs1, 0x7FF0000000000000
+  %sel = select i1 %cmp, double -0.000000e+00, double %abs1
+  %abs2 = call double @llvm.fabs.f64(double %sel)
+  ret double %abs2
+}
diff --git a/llvm/test/Transforms/InstCombine/simplify-demanded-fpclass.ll b/llvm/test/Transforms/InstCombine/simplify-demanded-fpclass.ll
index 5dfeb0734fbbed..a7d01b4f824db0 100644
--- a/llvm/test/Transforms/InstCombine/simplify-demanded-fpclass.ll
+++ b/llvm/test/Transforms/InstCombine/simplify-demanded-fpclass.ll
@@ -387,8 +387,8 @@ define nofpclass(inf) float @ret_nofpclass_inf__fabs_select_pinf_rhs(i1 %cond, f
 define nofpclass(ninf nnorm nsub nzero) float @ret_nofpclass_no_negatives__fabs_select_pinf_rhs(i1 %cond, float %x) {
 ; CHECK-LABEL: define nofpclass(ninf nzero nsub nnorm) float @ret_nofpclass_no_negatives__fabs_select_pinf_rhs
 ; CHECK-SAME: (i1 [[COND:%.*]], float [[X:%.*]]) {
-; CHECK-NEXT:    [[SELECT:%.*]] = select i1 [[COND]], float [[X]], float 0x7FF0000000000000
-; CHECK-NEXT:    [[FABS:%.*]] = call float @llvm.fabs.f32(float [[SELECT]])
+; CHECK-NEXT:    [[TMP1:%.*]] = call float @llvm.fabs.f32(float [[X]])
+; CHECK-NEXT:    [[FABS:%.*]] = select i1 [[COND]], float [[TMP1]], float 0x7FF0000000000000
 ; CHECK-NEXT:    ret float [[FABS]]
 ;
   %select = select i1 %cond, float %x, float 0x7FF0000000000000
@@ -411,8 +411,8 @@ define nofpclass(pinf pnorm psub pzero) float @ret_nofpclass_no_positives__fabs_
 define nofpclass(nan ninf nnorm nsub nzero) float @ret_nofpclass_no_negatives_nan__fabs_select_pinf_rhs(i1 %cond, float %x) {
 ; CHECK-LABEL: define nofpclass(nan ninf nzero nsub nnorm) float @ret_nofpclass_no_negatives_nan__fabs_select_pinf_rhs
 ; CHECK-SAME: (i1 [[COND:%.*]], float [[X:%.*]]) {
-; CHECK-NEXT:    [[SELECT:%.*]] = select i1 [[COND]], float [[X]], float 0x7FF0000000000000
-; CHECK-NEXT:    [[FABS:%.*]] = call float @llvm.fabs.f32(float [[SELECT]])
+; CHECK-NEXT:    [[TMP1:%.*]] = call float @llvm.fabs.f32(float [[X]])
+; CHECK-NEXT:    [[FABS:%.*]] = select i1 [[COND]], float [[TMP1]], float 0x7FF0000000000000
 ; CHECK-NEXT:    ret float [[FABS]]
 ;
   %select = select i1 %cond, float %x, float 0x7FF0000000000000
@@ -665,8 +665,8 @@ define nofpclass(inf pnorm psub pzero) float @ret_nofpclass_no_positives_noinf__
 define nofpclass(ninf nnorm nsub nzero) float @ret_nofpclass_no_negatives__copysign_unknown_select_pinf_rhs(i1 %cond, float %x, float %unknown.sign) {
 ; CHECK-LABEL: define nofpclass(ninf nzero nsub nnorm) float @ret_nofpclass_no_negatives__copysign_unknown_select_pinf_rhs
 ; CHECK-SAME: (i1 [[COND:%.*]], float [[X:%.*]], float [[UNKNOWN_SIGN:%.*]]) {
-; CHECK-NEXT:    [[SELECT:%.*]] = select i1 [[COND]], float [[X]], float 0x7FF0000000000000
-; CHECK-NEXT:    [[COPYSIGN:%.*]] = call float @llvm.fabs.f32(float [[SELECT]])
+; CHECK-NEXT:    [[TMP1:%.*]] = call float @llvm.fabs.f32(float [[X]])
+; CHECK-NEXT:    [[COPYSIGN:%.*]] = select i1 [[COND]], float [[TMP1]], float 0x7FF0000000000000
 ; CHECK-NEXT:    ret float [[COPYSIGN]]
 ;
   %select = select i1 %cond, float %x, float 0x7FF0000000000000
@@ -678,8 +678,8 @@ define nofpclass(ninf nnorm nsub nzero) float @ret_nofpclass_no_negatives__copys
 define nofpclass(pinf pnorm psub pzero) float @ret_nofpclass_no_positives__copysign_unknown_select_pinf_rhs(i1 %cond, float %x, float %unknown.sign) {
 ; CHECK-LABEL: define nofpclass(pinf pzero psub pnorm) float @ret_nofpclass_no_positives__copysign_unknown_select_pinf_rhs
 ; CHECK-SAME: (i1 [[COND:%.*]], float [[X:%.*]], float [[UNKNOWN_SIGN:%.*]]) {
-; CHECK-NEXT:    [[SELECT:%.*]] = select i1 [[COND]], float [[X]], float 0x7FF0000000000000
-; CHECK-NEXT:    [[TMP1:%.*]] = call float @llvm.fabs.f32(float [[SELECT]])
+; CHECK-NEXT:    [[TMP2:%.*]] = call float @llvm.fabs.f32(float [[X]])
+; CHECK-NEXT:    [[TMP1:%.*]] = select i1 [[COND]], float [[TMP2]], float 0x7FF0000000000000
 ; CHECK-NEXT:    [[COPYSIGN:%.*]] = fneg float [[TMP1]]
 ; CHECK-NEXT:    ret float [[COPYSIGN]]
 ;
@@ -692,8 +692,8 @@ define nofpclass(pinf pnorm psub pzero) float @ret_nofpclass_no_positives__copys
 define nofpclass(nan ninf nnorm nsub nzero) float @ret_nofpclass_no_negatives_nonan__copysign_unknown_select_pinf_rhs(i1 %cond, float %x, float %unknown.sign) {
 ; CHECK-LABEL: define nofpclass(nan ninf nzero nsub nnorm) float @ret_nofpclass_no_negatives_nonan__copysign_unknown_select_pinf_rhs
 ; CHECK-SAME: (i1 [[COND:%.*]], float [[X:%.*]], float [[UNKNOWN_SIGN:%.*]]) {
-; CHECK-NEXT:    [[SELECT:%.*]] = select i1 [[COND]], float [[X]], float 0x7FF0000000000000
-; CHECK-NEXT:    [[COPYSIGN:%.*]] = call float @llvm.fabs.f32(float [[SELECT]])
+; CHECK-NEXT:    [[TMP1:%.*]] = call float @llvm.fabs.f32(float [[X]])
+; CHECK-NEXT:    [[COPYSIGN:%.*]] = select i1 [[COND]], float [[TMP1]], float 0x7FF0000000000000
 ; CHECK-NEXT:    ret float [[COPYSIGN]]
 ;
   %select = select i1 %cond, float %x, float 0x7FF0000000000000
@@ -705,8 +705,8 @@ define nofpclass(nan ninf nnorm nsub nzero) float @ret_nofpclass_no_negatives_no
 define nofpclass(nan pinf pnorm psub pzero) float @ret_nofpclass_no_positives_nonan__copysign_unknown_select_pinf_rhs(i1 %cond, float %x, float %unknown.sign) {
 ; CHECK-LABEL: define nofpclass(nan pinf pzero psub pnorm) float @ret_nofpclass_no_positives_nonan__copysign_unknown_select_pinf_rhs
 ; CHECK-SAME: (i1 [[COND:%.*]], float [[X:%.*]], float [[UNKNOWN_SIGN:%.*]]) {
-; CHECK-NEXT:    [[SELECT:%.*]] = select i1 [[COND]], float [[X]], float 0x7FF0000000000000
-; CHECK-NEXT:    [[TMP1:%.*]] = call float @llvm.fabs.f32(float [[SELECT]])
+; CHECK-NEXT:    [[TMP2:%.*]] = call float @llvm.fabs.f32(float [[X]])
+; CHECK-NEXT:    [[TMP1:%.*]] = select i1 [[COND]], float [[TMP2]], float 0x7FF0000000000000
 ; CHECK-NEXT:    [[COPYSIGN:%.*]] = fneg float [[TMP1]]
 ; CHECK-NEXT:    ret float [[COPYSIGN]]
 ;

PR Link: llvm/llvm-project#86390

github-actions · 2024-03-23T10:35:12Z

✅ With the latest revision this PR passed the C/C++ code formatter.

github-actions · 2024-03-23T10:35:12Z

✅ With the latest revision this PR passed the Python code formatter.

arsenm · 2024-03-26T07:36:37Z

llvm/test/Transforms/InstCombine/intrinsic-select.ll

+  %sel = select i1 %cmp, double -0.000000e+00, double %abs1
+  %abs2 = call double @llvm.fabs.f64(double %sel)
+  ret double %abs2
+}


Test vectors and flag preservation

Do we handle fneg? Does the fneg+fabs combo fold the same?

Test vectors and flag preservation

Done. Alive2: https://alive2.llvm.org/ce/z/ijP-me

Do we handle fneg?

No.

Does the fneg+fabs combo fold the same?

Can you explain it a bit more?

I mean the same should be applied with fneg, and with fneg(fabs(x))

arsenm

This is probably worse if the constant is some weird constant expression, but that's rare.

We should do the same for fneg next.

As we folds fabs over select in #86390, this patch folds fneg over select to make sure nabs idioms are generated. Addresses #86390 (comment). Alive2 for FMF propagation: https://alive2.llvm.org/ce/z/-h6Vuo

dtcxzyw requested review from arsenm and goldsteinn March 23, 2024 10:32

dtcxzyw requested a review from nikic as a code owner March 23, 2024 10:32

llvmbot added the llvm:transforms label Mar 23, 2024

dtcxzyw added a commit to dtcxzyw/llvm-opt-benchmark that referenced this pull request Mar 23, 2024

pre-commit: test PR86390

1f21358

PR Link: llvm/llvm-project#86390

dtcxzyw mentioned this pull request Mar 23, 2024

pre-commit: test PR86390 dtcxzyw/llvm-opt-benchmark#450

Closed

arsenm reviewed Mar 26, 2024

View reviewed changes

[InstCombine] Add pre-commit tests. NFC.

aef2236

dtcxzyw force-pushed the perf/fabs-select branch from b65d65f to f6e18bf Compare April 11, 2024 13:24

[InstCombine] Fold fabs over select

f6d142a

dtcxzyw force-pushed the perf/fabs-select branch from f6e18bf to f6d142a Compare April 11, 2024 13:32

arsenm approved these changes Apr 17, 2024

View reviewed changes

dtcxzyw merged commit d18ab0e into llvm:main Apr 22, 2024
3 of 4 checks passed

dtcxzyw deleted the perf/fabs-select branch April 22, 2024 07:37

This was referenced Apr 22, 2024

[libc] Make fenv and math tests preserve fenv_t state #89658

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[libc] Clean up alternate test framework support #89659

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dtcxzyw mentioned this pull request Apr 24, 2024

[InstCombine] Fold fneg over select #89947

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[InstCombine] Fold fabs over selects #86390

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edited

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[InstCombine] Fold fabs over selects #86390

[InstCombine] Fold fabs over selects #86390

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dtcxzyw commented Mar 23, 2024

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github-actions bot commented Mar 23, 2024 • edited

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github-actions bot commented Mar 23, 2024 •

edited