[llvm] Fold intrinsics over multi-use selects when the intrinsic is the only user (PR #172723)

[via llvm-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-llvm-transforms

Author: Sayan Sivakumaran (sivakusayan)

<details>
<summary>Changes</summary>

Closes #<!-- -->172176.

Previously, `FoldOpIntoSelect` wouldn't fold multi-use selects if `MultiUse` wasn't explicitly true. This prevents useful folding when the select is used multiple times in the same intrinsic call. Similar to what is done in `foldOpIntoPhi`, we'll now check that all of the uses come from a single user, rather than checking that there is only one use.

---
Full diff: https://github.com/llvm/llvm-project/pull/172723.diff


2 Files Affected:

- (modified) llvm/lib/Transforms/InstCombine/InstructionCombining.cpp (+1-1) 
- (modified) llvm/test/Transforms/InstCombine/intrinsic-select.ll (+124) 


``````````diff
diff --git a/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp b/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
index 14244236d75d5..2272cb868160f 100644
--- a/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
@@ -1783,7 +1783,7 @@ Instruction *InstCombinerImpl::FoldOpIntoSelect(Instruction &Op, SelectInst *SI,
                                                 bool FoldWithMultiUse,
                                                 bool SimplifyBothArms) {
   // Don't modify shared select instructions unless set FoldWithMultiUse
-  if (!SI->hasOneUse() && !FoldWithMultiUse)
+  if (!SI->hasOneUser() && !FoldWithMultiUse)
     return nullptr;
 
   Value *TV = SI->getTrueValue();
diff --git a/llvm/test/Transforms/InstCombine/intrinsic-select.ll b/llvm/test/Transforms/InstCombine/intrinsic-select.ll
index 38cf02dc2a795..ac2ad1f9837a2 100644
--- a/llvm/test/Transforms/InstCombine/intrinsic-select.ll
+++ b/llvm/test/Transforms/InstCombine/intrinsic-select.ll
@@ -426,3 +426,127 @@ define { <4 x float>, <4 x float> } @test_select_of_sincos_intrinsic_operand(<4
   %result = call { <4 x float>, <4 x float> } @llvm.sincos.v4f32(<4 x float> %s)
   ret { <4 x float>, <4 x float> } %result
 }
+
+define i8 @test_select_rotate_left(i1 %0) {
+; CHECK-LABEL: @test_select_rotate_left(
+; CHECK-NEXT:    [[RET:%.*]] = select i1 [[TMP0:%.*]], i8 2, i8 -1
+; CHECK-NEXT:    ret i8 [[RET]]
+;
+  %s = select i1 %0, i8 1, i8 -1
+  %ret = call i8 @llvm.fshl.i8(i8 %s, i8 %s, i8 1)
+  ret i8 %ret
+}
+
+define i8 @test_select_rotate_left_poison(i1 %0) {
+; CHECK-LABEL: @test_select_rotate_left_poison(
+; CHECK-NEXT:    ret i8 -1
+;
+  %s = select i1 %0, i8 poison, i8 -1
+  %ret = call i8 @llvm.fshl.i8(i8 %s, i8 %s, i8 1)
+  ret i8 %ret
+}
+
+define i8 @test_select_rotate_left_multiuser(i1 %0) {
+; CHECK-LABEL: @test_select_rotate_left_multiuser(
+; CHECK-NEXT:    [[S:%.*]] = select i1 [[TMP0:%.*]], i8 1, i8 -1
+; CHECK-NEXT:    [[RET:%.*]] = call i8 @llvm.fshl.i8(i8 [[S]], i8 [[S]], i8 1)
+; CHECK-NEXT:    call void @use(i8 [[S]])
+; CHECK-NEXT:    ret i8 [[RET]]
+;
+  %s = select i1 %0, i8 1, i8 -1
+  %ret = call i8 @llvm.fshl.i8(i8 %s, i8 %s, i8 1)
+  call void @use(i8 %s)
+  ret i8 %ret
+}
+
+define <2 x i8> @test_select_rotate_left_splat(i1 %0) {
+; CHECK-LABEL: @test_select_rotate_left_splat(
+; CHECK-NEXT:    [[RET:%.*]] = select i1 [[TMP0:%.*]], <2 x i8> splat (i8 2), <2 x i8> splat (i8 -1)
+; CHECK-NEXT:    ret <2 x i8> [[RET]]
+;
+  %s = select i1 %0, <2 x i8> <i8 1, i8 1>, <2 x i8> <i8 -1, i8 -1>
+  %ret = call <2 x i8> @llvm.fshl.v2i8(<2 x i8> %s, <2 x i8> %s, <2 x i8> <i8 1, i8 1>)
+  ret <2 x i8> %ret
+}
+
+define <2 x i8> @test_select_rotate_left_splat_poison(i1 %0) {
+; CHECK-LABEL: @test_select_rotate_left_splat_poison(
+; CHECK-NEXT:    [[RET:%.*]] = select i1 [[TMP0:%.*]], <2 x i8> <i8 2, i8 poison>, <2 x i8> splat (i8 -1)
+; CHECK-NEXT:    ret <2 x i8> [[RET]]
+;
+  %s = select i1 %0, <2 x i8> <i8 1, i8 poison>, <2 x i8> <i8 -1, i8 -1>
+  %ret = call <2 x i8> @llvm.fshl.v2i8(<2 x i8> %s, <2 x i8> %s, <2 x i8> <i8 1, i8 1>)
+  ret <2 x i8> %ret
+}
+
+define <2 x i8> @test_select_rotate_left_non_splat(i1 %0) {
+; CHECK-LABEL: @test_select_rotate_left_non_splat(
+; CHECK-NEXT:    [[RET:%.*]] = select i1 [[TMP0:%.*]], <2 x i8> <i8 2, i8 4>, <2 x i8> <i8 -1, i8 -3>
+; CHECK-NEXT:    ret <2 x i8> [[RET]]
+;
+  %s = select i1 %0, <2 x i8> <i8 1, i8 2>, <2 x i8> <i8 -1, i8 -2>
+  %ret = call <2 x i8> @llvm.fshl.v2i8(<2 x i8> %s, <2 x i8> %s, <2 x i8> <i8 1, i8 1>)
+  ret <2 x i8> %ret
+}
+
+define i8 @test_select_rotate_right(i1 %0) {
+; CHECK-LABEL: @test_select_rotate_right(
+; CHECK-NEXT:    [[RET:%.*]] = select i1 [[TMP0:%.*]], i8 2, i8 -1
+; CHECK-NEXT:    ret i8 [[RET]]
+;
+  %s = select i1 %0, i8 1, i8 -1
+  %ret = call i8 @llvm.fshr.i8(i8 %s, i8 %s, i8 7)
+  ret i8 %ret
+}
+
+define i8 @test_select_rotate_right_poison_args(i1 %0) {
+; CHECK-LABEL: @test_select_rotate_right_poison_args(
+; CHECK-NEXT:    ret i8 -1
+;
+  %s = select i1 %0, i8 poison, i8 -1
+  %ret = call i8 @llvm.fshr.i8(i8 %s, i8 %s, i8 7)
+  ret i8 %ret
+}
+
+define i8 @test_select_rotate_right_multiuser(i1 %0) {
+; CHECK-LABEL: @test_select_rotate_right_multiuser(
+; CHECK-NEXT:    [[S:%.*]] = select i1 [[TMP0:%.*]], i8 1, i8 -1
+; CHECK-NEXT:    [[RET:%.*]] = call i8 @llvm.fshl.i8(i8 [[S]], i8 [[S]], i8 1)
+; CHECK-NEXT:    call void @use(i8 [[S]])
+; CHECK-NEXT:    ret i8 [[RET]]
+;
+  %s = select i1 %0, i8 1, i8 -1
+  %ret = call i8 @llvm.fshr.i8(i8 %s, i8 %s, i8 7)
+  call void @use(i8 %s)
+  ret i8 %ret
+}
+
+define <2 x i8> @test_select_rotate_right_splat(i1 %0) {
+; CHECK-LABEL: @test_select_rotate_right_splat(
+; CHECK-NEXT:    [[RET:%.*]] = select i1 [[TMP0:%.*]], <2 x i8> splat (i8 2), <2 x i8> splat (i8 -1)
+; CHECK-NEXT:    ret <2 x i8> [[RET]]
+;
+  %s = select i1 %0, <2 x i8> <i8 1, i8 1>, <2 x i8> <i8 -1, i8 -1>
+  %ret = call <2 x i8> @llvm.fshr.v2i8(<2 x i8> %s, <2 x i8> %s, <2 x i8> <i8 7, i8 7>)
+  ret <2 x i8> %ret
+}
+
+define <2 x i8> @test_select_rotate_right_splat_poison(i1 %0) {
+; CHECK-LABEL: @test_select_rotate_right_splat_poison(
+; CHECK-NEXT:    [[RET:%.*]] = select i1 [[TMP0:%.*]], <2 x i8> <i8 2, i8 poison>, <2 x i8> splat (i8 -1)
+; CHECK-NEXT:    ret <2 x i8> [[RET]]
+;
+  %s = select i1 %0, <2 x i8> <i8 1, i8 poison>, <2 x i8> <i8 -1, i8 -1>
+  %ret = call <2 x i8> @llvm.fshr.v2i8(<2 x i8> %s, <2 x i8> %s, <2 x i8> <i8 7, i8 7>)
+  ret <2 x i8> %ret
+}
+
+define <2 x i8> @test_select_rotate_right_non_splat(i1 %0) {
+; CHECK-LABEL: @test_select_rotate_right_non_splat(
+; CHECK-NEXT:    [[RET:%.*]] = select i1 [[TMP0:%.*]], <2 x i8> <i8 2, i8 4>, <2 x i8> <i8 -1, i8 -3>
+; CHECK-NEXT:    ret <2 x i8> [[RET]]
+;
+  %s = select i1 %0, <2 x i8> <i8 1, i8 2>, <2 x i8> <i8 -1, i8 -2>
+  %ret = call <2 x i8> @llvm.fshr.v2i8(<2 x i8> %s, <2 x i8> %s, <2 x i8> <i8 7, i8 7>)
+  ret <2 x i8> %ret
+}

``````````

</details>


https://github.com/llvm/llvm-project/pull/172723