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

This patch folds `fabs(-x) -> fabs(x)`

Closes #94170

Proofs: https://alive2.llvm.org/ce/z/gjzmgf

2 files changed, 196 insertions, 4 deletions

diff --git a/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp b/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
index 56bd79f..921ed6e 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
@@ -2511,16 +2511,22 @@ Instruction *InstCombinerImpl::visitCallInst(CallInst &CI) {
   }
   case Intrinsic::fabs: {
     Value *Cond, *TVal, *FVal;
-    if (match(II->getArgOperand(0),
-              m_Select(m_Value(Cond), m_Value(TVal), m_Value(FVal)))) {
+    Value *Arg = II->getArgOperand(0);
+    Value *X;
+    // fabs (-X) --> fabs (X)
+    if (match(Arg, m_FNeg(m_Value(X)))) {
+        CallInst *Fabs = Builder.CreateUnaryIntrinsic(Intrinsic::fabs, X, II);
+        return replaceInstUsesWith(CI, Fabs);
+    }
+
+    if (match(Arg, m_Select(m_Value(Cond), m_Value(TVal), m_Value(FVal)))) {
       // fabs (select Cond, TrueC, FalseC) --> select Cond, AbsT, AbsF
       if (isa<Constant>(TVal) || isa<Constant>(FVal)) {
         CallInst *AbsT = Builder.CreateCall(II->getCalledFunction(), {TVal});
         CallInst *AbsF = Builder.CreateCall(II->getCalledFunction(), {FVal});
         SelectInst *SI = SelectInst::Create(Cond, AbsT, AbsF);
         FastMathFlags FMF1 = II->getFastMathFlags();
-        FastMathFlags FMF2 =
-            cast<SelectInst>(II->getArgOperand(0))->getFastMathFlags();
+        FastMathFlags FMF2 = cast<SelectInst>(Arg)->getFastMathFlags();
         FMF2.setNoSignedZeros(false);
         SI->setFastMathFlags(FMF1 | FMF2);
         return SI;
diff --git a/llvm/test/Transforms/InstCombine/fabs-fneg-fold.ll b/llvm/test/Transforms/InstCombine/fabs-fneg-fold.ll
new file mode 100644
index 0000000..a1988e5
--- /dev/null
+++ b/llvm/test/Transforms/InstCombine/fabs-fneg-fold.ll
@@ -0,0 +1,186 @@
+; 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_copysign_nnan(float %x, float %y) {
+; CHECK-LABEL: define float @fabs_copysign_nnan(
+; CHECK-SAME: float [[X:%.*]], float [[Y:%.*]]) {
+; CHECK-NEXT:    [[FABS:%.*]] = call nnan float @llvm.fabs.f32(float [[X]])
+; CHECK-NEXT:    ret float [[FABS]]
+;
+  %copysign = call float @llvm.copysign.f32(float %x, float %y)
+  %fabs = call nnan float @llvm.fabs.f32(float %copysign)
+  ret float %fabs
+}
+
+
+define float @fabs_copysign_ninf(float %x, float %y) {
+; CHECK-LABEL: define float @fabs_copysign_ninf(
+; CHECK-SAME: float [[X:%.*]], float [[Y:%.*]]) {
+; CHECK-NEXT:    [[FABS:%.*]] = call ninf float @llvm.fabs.f32(float [[X]])
+; CHECK-NEXT:    ret float [[FABS]]
+;
+  %copysign = call float @llvm.copysign.f32(float %x, float %y)
+  %fabs = call ninf float @llvm.fabs.f32(float %copysign)
+  ret float %fabs
+}
+
+define float @fabs_copysign_nsz(float %x, float %y) {
+; CHECK-LABEL: define float @fabs_copysign_nsz(
+; CHECK-SAME: float [[X:%.*]], float [[Y:%.*]]) {
+; CHECK-NEXT:    [[FABS:%.*]] = call nsz float @llvm.fabs.f32(float [[X]])
+; CHECK-NEXT:    ret float [[FABS]]
+;
+  %copysign = call float @llvm.copysign.f32(float %x, float %y)
+  %fabs = call nsz float @llvm.fabs.f32(float %copysign)
+  ret float %fabs
+}
+
+define float @fabs_copysign_nnan_negative(float %x, float %y) {
+; CHECK-LABEL: define float @fabs_copysign_nnan_negative(
+; CHECK-SAME: float [[X:%.*]], float [[Y:%.*]]) {
+; CHECK-NEXT:    [[FABS:%.*]] = call nnan float @llvm.fabs.f32(float [[X]])
+; CHECK-NEXT:    ret float [[FABS]]
+;
+  %copysign = call float @llvm.copysign.f32(float %x, float %y)
+  %fabs = call nnan float @llvm.fabs.f32(float %copysign)
+  ret float %fabs
+}
+
+
+define float @fabs_copysign_ninf_negative(float %x, float %y) {
+; CHECK-LABEL: define float @fabs_copysign_ninf_negative(
+; CHECK-SAME: float [[X:%.*]], float [[Y:%.*]]) {
+; CHECK-NEXT:    [[FABS:%.*]] = call ninf float @llvm.fabs.f32(float [[X]])
+; CHECK-NEXT:    ret float [[FABS]]
+;
+  %copysign = call float @llvm.copysign.f32(float %x, float %y)
+  %fabs = call ninf float @llvm.fabs.f32(float %copysign)
+  ret float %fabs
+}
+
+define float @fabs_copysign_nsz_negative(float %x, float %y) {
+; CHECK-LABEL: define float @fabs_copysign_nsz_negative(
+; CHECK-SAME: float [[X:%.*]], float [[Y:%.*]]) {
+; CHECK-NEXT:    [[FABS:%.*]] = call nsz float @llvm.fabs.f32(float [[X]])
+; CHECK-NEXT:    ret float [[FABS]]
+;
+  %copysign = call float @llvm.copysign.f32(float %x, float %y)
+  %fabs = call nsz float @llvm.fabs.f32(float %copysign)
+  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
+}
+
+
+