[llvm] [InstCombine] Add fold for fabs(-x) -> fabs(x) (PR #95627)

[via llvm-commits]

================
@@ -0,0 +1,138 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 5
+; RUN: opt -S -passes=instcombine %s | FileCheck %s
+
+define float @fabs_fneg_basic(float %x) {
+; CHECK-LABEL: define float @fabs_fneg_basic(
+; CHECK-SAME: float [[X:%.*]]) {
+; CHECK-NEXT:    [[FABS:%.*]] = call float @llvm.fabs.f32(float [[X]])
+; CHECK-NEXT:    ret float [[FABS]]
+;
+  %neg = fneg float %x
+  %fabs = call float @llvm.fabs.f32(float %neg)
+  ret float %fabs
+}
+
+define <2 x float> @fabs_fneg_v2f32(<2 x float> %x) {
+; CHECK-LABEL: define <2 x float> @fabs_fneg_v2f32(
+; CHECK-SAME: <2 x float> [[X:%.*]]) {
+; CHECK-NEXT:    [[FABS:%.*]] = call <2 x float> @llvm.fabs.v2f32(<2 x float> [[X]])
+; CHECK-NEXT:    ret <2 x float> [[FABS]]
+;
+  %neg = fneg <2 x float> %x
+  %fabs = call <2 x float> @llvm.fabs.v2f32(<2 x float> %neg)
+  ret <2 x float> %fabs
+}
+
+define double @fabs_fneg_f64(double %x) {
+; CHECK-LABEL: define double @fabs_fneg_f64(
+; CHECK-SAME: double [[X:%.*]]) {
+; CHECK-NEXT:    [[FABS:%.*]] = call double @llvm.fabs.f64(double [[X]])
+; CHECK-NEXT:    ret double [[FABS]]
+;
+  %neg = fneg double %x
+  %fabs = call double @llvm.fabs.f64(double %neg)
+  ret double %fabs
+}
+
+define <4 x double> @fabs_fneg_v4f64(<4 x double> %x) {
+; CHECK-LABEL: define <4 x double> @fabs_fneg_v4f64(
+; CHECK-SAME: <4 x double> [[X:%.*]]) {
+; CHECK-NEXT:    [[FABS:%.*]] = call <4 x double> @llvm.fabs.v4f64(<4 x double> [[X]])
+; CHECK-NEXT:    ret <4 x double> [[FABS]]
+;
+  %neg = fneg <4 x double> %x
+  %fabs = call <4 x double> @llvm.fabs.v4f64(<4 x double> %neg)
+  ret <4 x double> %fabs
+}
+
+define half @fabs_fneg_f16(half %x) {
+; CHECK-LABEL: define half @fabs_fneg_f16(
+; CHECK-SAME: half [[X:%.*]]) {
+; CHECK-NEXT:    [[FABS:%.*]] = call half @llvm.fabs.f16(half [[X]])
+; CHECK-NEXT:    ret half [[FABS]]
+;
+  %neg = fneg half %x
+  %fabs = call half @llvm.fabs.f16(half %neg)
+  ret half %fabs
+}
+
+define float @fabs_fneg_nnan(float %x) {
+; CHECK-LABEL: define float @fabs_fneg_nnan(
+; CHECK-SAME: float [[X:%.*]]) {
+; CHECK-NEXT:    [[FABS:%.*]] = call float @llvm.fabs.f32(float [[X]])
+; CHECK-NEXT:    ret float [[FABS]]
+;
+  %neg = fneg nnan float %x
+  %fabs = call nnan float @llvm.fabs.f32(float %neg)
+  ret float %fabs
+}
+
+define float @fabs_fneg_ninf(float %x) {
+; CHECK-LABEL: define float @fabs_fneg_ninf(
+; CHECK-SAME: float [[X:%.*]]) {
+; CHECK-NEXT:    [[FABS:%.*]] = call float @llvm.fabs.f32(float [[X]])
+; CHECK-NEXT:    ret float [[FABS]]
+;
+  %neg = fneg ninf float %x
+  %fabs = call ninf float @llvm.fabs.f32(float %neg)
+  ret float %fabs
+}
+
+define float @fabs_fneg_no_fabs(float %x) {
+; CHECK-LABEL: define float @fabs_fneg_no_fabs(
+; CHECK-SAME: float [[X:%.*]]) {
+; CHECK-NEXT:    [[NEG:%.*]] = fneg float [[X]]
+; CHECK-NEXT:    ret float [[NEG]]
+;
+  %neg = fneg float %x
+  ret float %neg
+}
+
+define <2 x float> @fabs_fneg_splat_v2f32(<2 x float> %x) {
+; CHECK-LABEL: define <2 x float> @fabs_fneg_splat_v2f32(
+; CHECK-SAME: <2 x float> [[X:%.*]]) {
+; CHECK-NEXT:    ret <2 x float> <float 2.000000e+00, float 2.000000e+00>
+;
+  %neg = fneg <2 x float> <float -2.0, float -2.0>
+  %fabs = call <2 x float> @llvm.fabs.v2f32(<2 x float> %neg)
+  ret <2 x float> %fabs
+}
+
+
+define <2 x float> @fabs_fneg_splat_poison_v2f32(<2 x float> %x) {
+; CHECK-LABEL: define <2 x float> @fabs_fneg_splat_poison_v2f32(
+; CHECK-SAME: <2 x float> [[X:%.*]]) {
+; CHECK-NEXT:    [[FABS:%.*]] = call <2 x float> @llvm.fabs.v2f32(<2 x float> <float -2.000000e+00, float poison>)
+; CHECK-NEXT:    ret <2 x float> [[FABS]]
+;
+  %neg = fneg <2 x float> <float 2.0, float poison>
+  %fabs = call <2 x float> @llvm.fabs.v2f32(<2 x float> %neg)
+  ret <2 x float> %fabs
+}
+
+define <2 x float> @fabs_fneg_non_splat_v2f32(<2 x float> %x) {
+; CHECK-LABEL: define <2 x float> @fabs_fneg_non_splat_v2f32(
+; CHECK-SAME: <2 x float> [[X:%.*]]) {
+; CHECK-NEXT:    ret <2 x float> <float 2.000000e+00, float 3.000000e+00>
+;
+  %neg = fneg <2 x float> <float 2.0, float 3.0>
+  %fabs = call <2 x float> @llvm.fabs.v2f32(<2 x float> %neg)
+  ret <2 x float> %fabs
+}
+
+declare void @use(float)
+
+define float @fabs_fneg_multi_use(float %x) {
+; CHECK-LABEL: define float @fabs_fneg_multi_use(
+; CHECK-SAME: float [[X:%.*]]) {
+; CHECK-NEXT:    [[NEG:%.*]] = fneg float [[X]]
+; CHECK-NEXT:    call void @use(float [[NEG]])
+; CHECK-NEXT:    [[FABS:%.*]] = call float @llvm.fabs.f32(float [[X]])
+; CHECK-NEXT:    ret float [[FABS]]
+;
+  %neg = fneg float %x
+  call void @use(float %neg)
+  %fabs = call float @llvm.fabs.f32(float %neg)
+  ret float %fabs
+}
+
----------------
VaibhavRumale wrote:

Thank you for your feedback. I've added/changed the tests using copysign instead of fneg.

https://github.com/llvm/llvm-project/pull/95627