[llvm] [InstCombine] Fold `select Cond, not X, X` into `Cond ^ X` (PR #90089)
Yingwei Zheng via llvm-commits
llvm-commits at lists.llvm.org
Thu Apr 25 10:13:09 PDT 2024
https://github.com/dtcxzyw created https://github.com/llvm/llvm-project/pull/90089
See the following example:
```
define i1 @src(i64 %x, i1 %y) {
%1526 = icmp ne i64 %x, 0
%1527 = icmp eq i64 %x, 0
%sel = select i1 %y, i1 %1526, i1 %1527
ret i1 %sel
}
define i1 @tgt(i64 %x, i1 %y) {
%1527 = icmp eq i64 %x, 0
%sel = xor i1 %y, %1527
ret i1 %sel
}
```
I find that this pattern is common in C/C++/Rust code base.
This patch folds `select Cond, Y, X` into `Cond ^ X` iff:
1. X has the same type as Cond
2. X is poison -> Y is poison
3. X == !Y
Alive2: https://alive2.llvm.org/ce/z/hSmkHS
>From 6dffd8b83a7dec8bc40c425b5bb6e4a51e9ffc46 Mon Sep 17 00:00:00 2001
From: Yingwei Zheng <dtcxzyw2333 at gmail.com>
Date: Fri, 26 Apr 2024 01:04:57 +0800
Subject: [PATCH 1/2] [InstCombine] Add pre-commit tests. NFC.
---
.../test/Transforms/InstCombine/select-cmp.ll | 78 +++++++++++++++++++
1 file changed, 78 insertions(+)
diff --git a/llvm/test/Transforms/InstCombine/select-cmp.ll b/llvm/test/Transforms/InstCombine/select-cmp.ll
index 711fac542179f8..1188ded2f807ea 100644
--- a/llvm/test/Transforms/InstCombine/select-cmp.ll
+++ b/llvm/test/Transforms/InstCombine/select-cmp.ll
@@ -345,4 +345,82 @@ define i1 @icmp_no_common(i1 %c, i8 %x, i8 %y, i8 %z) {
ret i1 %r
}
+define i1 @test_select_inverse1(i64 %x, i1 %y) {
+; CHECK-LABEL: @test_select_inverse1(
+; CHECK-NEXT: [[CMP1:%.*]] = icmp ne i64 [[X:%.*]], 0
+; CHECK-NEXT: [[CMP2:%.*]] = icmp eq i64 [[X]], 0
+; CHECK-NEXT: [[SEL:%.*]] = select i1 [[Y:%.*]], i1 [[CMP1]], i1 [[CMP2]]
+; CHECK-NEXT: ret i1 [[SEL]]
+;
+ %cmp1 = icmp ne i64 %x, 0
+ %cmp2 = icmp eq i64 %x, 0
+ %sel = select i1 %y, i1 %cmp1, i1 %cmp2
+ ret i1 %sel
+}
+
+define i1 @test_select_inverse2(i64 %x, i1 %y) {
+; CHECK-LABEL: @test_select_inverse2(
+; CHECK-NEXT: [[CMP1:%.*]] = icmp sgt i64 [[X:%.*]], -1
+; CHECK-NEXT: [[CMP2:%.*]] = icmp slt i64 [[X]], 0
+; CHECK-NEXT: [[SEL:%.*]] = select i1 [[Y:%.*]], i1 [[CMP1]], i1 [[CMP2]]
+; CHECK-NEXT: ret i1 [[SEL]]
+;
+ %cmp1 = icmp sgt i64 %x, -1
+ %cmp2 = icmp slt i64 %x, 0
+ %sel = select i1 %y, i1 %cmp1, i1 %cmp2
+ ret i1 %sel
+}
+
+define i1 @test_select_inverse3(ptr %x, i1 %y) {
+; CHECK-LABEL: @test_select_inverse3(
+; CHECK-NEXT: [[CMP1:%.*]] = icmp eq ptr [[X:%.*]], null
+; CHECK-NEXT: [[CMP2:%.*]] = icmp ne ptr [[X]], null
+; CHECK-NEXT: [[SEL:%.*]] = select i1 [[Y:%.*]], i1 [[CMP1]], i1 [[CMP2]]
+; CHECK-NEXT: ret i1 [[SEL]]
+;
+ %cmp1 = icmp eq ptr %x, null
+ %cmp2 = icmp ne ptr %x, null
+ %sel = select i1 %y, i1 %cmp1, i1 %cmp2
+ ret i1 %sel
+}
+
+define i1 @test_select_inverse_fail(i64 %x, i1 %y) {
+; CHECK-LABEL: @test_select_inverse_fail(
+; CHECK-NEXT: [[CMP1:%.*]] = icmp sgt i64 [[X:%.*]], 0
+; CHECK-NEXT: [[CMP2:%.*]] = icmp slt i64 [[X]], 0
+; CHECK-NEXT: [[SEL:%.*]] = select i1 [[Y:%.*]], i1 [[CMP1]], i1 [[CMP2]]
+; CHECK-NEXT: ret i1 [[SEL]]
+;
+ %cmp1 = icmp sgt i64 %x, 0
+ %cmp2 = icmp slt i64 %x, 0
+ %sel = select i1 %y, i1 %cmp1, i1 %cmp2
+ ret i1 %sel
+}
+
+define <2 x i1> @test_select_inverse_vec(<2 x i64> %x, <2 x i1> %y) {
+; CHECK-LABEL: @test_select_inverse_vec(
+; CHECK-NEXT: [[CMP1:%.*]] = icmp ne <2 x i64> [[X:%.*]], zeroinitializer
+; CHECK-NEXT: [[CMP2:%.*]] = icmp eq <2 x i64> [[X]], zeroinitializer
+; CHECK-NEXT: [[SEL:%.*]] = select <2 x i1> [[Y:%.*]], <2 x i1> [[CMP1]], <2 x i1> [[CMP2]]
+; CHECK-NEXT: ret <2 x i1> [[SEL]]
+;
+ %cmp1 = icmp ne <2 x i64> %x, zeroinitializer
+ %cmp2 = icmp eq <2 x i64> %x, zeroinitializer
+ %sel = select <2 x i1> %y, <2 x i1> %cmp1, <2 x i1> %cmp2
+ ret <2 x i1> %sel
+}
+
+define <2 x i1> @test_select_inverse_vec_fail(<2 x i64> %x, i1 %y) {
+; CHECK-LABEL: @test_select_inverse_vec_fail(
+; CHECK-NEXT: [[CMP1:%.*]] = icmp ne <2 x i64> [[X:%.*]], zeroinitializer
+; CHECK-NEXT: [[CMP2:%.*]] = icmp eq <2 x i64> [[X]], zeroinitializer
+; CHECK-NEXT: [[SEL:%.*]] = select i1 [[Y:%.*]], <2 x i1> [[CMP1]], <2 x i1> [[CMP2]]
+; CHECK-NEXT: ret <2 x i1> [[SEL]]
+;
+ %cmp1 = icmp ne <2 x i64> %x, zeroinitializer
+ %cmp2 = icmp eq <2 x i64> %x, zeroinitializer
+ %sel = select i1 %y, <2 x i1> %cmp1, <2 x i1> %cmp2
+ ret <2 x i1> %sel
+}
+
declare void @use(i1)
>From ac7ded456af70c1c10f64dac4b7093b41aa9eccd Mon Sep 17 00:00:00 2001
From: Yingwei Zheng <dtcxzyw2333 at gmail.com>
Date: Fri, 26 Apr 2024 01:06:51 +0800
Subject: [PATCH 2/2] [InstCombine] Fold `select Cond, not X, X` into `Cond ^
X`
---
.../InstCombine/InstCombineSelect.cpp | 5 +++++
.../test/Transforms/InstCombine/select-cmp.ll | 20 ++++++++-----------
2 files changed, 13 insertions(+), 12 deletions(-)
diff --git a/llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp b/llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp
index 117eb7a1dcc933..69341c8d3f41cf 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp
@@ -3985,5 +3985,10 @@ Instruction *InstCombinerImpl::visitSelectInst(SelectInst &SI) {
}
}
+ if (CondVal->getType() == SI.getType() && impliesPoison(FalseVal, TrueVal) &&
+ isImpliedCondition(FalseVal, TrueVal, DL, /*LHSIsTrue=*/true) == false &&
+ isImpliedCondition(FalseVal, TrueVal, DL, /*LHSIsTrue=*/false) == true)
+ return BinaryOperator::CreateXor(CondVal, FalseVal);
+
return nullptr;
}
diff --git a/llvm/test/Transforms/InstCombine/select-cmp.ll b/llvm/test/Transforms/InstCombine/select-cmp.ll
index 1188ded2f807ea..3ec89af8d868c7 100644
--- a/llvm/test/Transforms/InstCombine/select-cmp.ll
+++ b/llvm/test/Transforms/InstCombine/select-cmp.ll
@@ -347,9 +347,8 @@ define i1 @icmp_no_common(i1 %c, i8 %x, i8 %y, i8 %z) {
define i1 @test_select_inverse1(i64 %x, i1 %y) {
; CHECK-LABEL: @test_select_inverse1(
-; CHECK-NEXT: [[CMP1:%.*]] = icmp ne i64 [[X:%.*]], 0
-; CHECK-NEXT: [[CMP2:%.*]] = icmp eq i64 [[X]], 0
-; CHECK-NEXT: [[SEL:%.*]] = select i1 [[Y:%.*]], i1 [[CMP1]], i1 [[CMP2]]
+; CHECK-NEXT: [[CMP2:%.*]] = icmp eq i64 [[X:%.*]], 0
+; CHECK-NEXT: [[SEL:%.*]] = xor i1 [[CMP2]], [[Y:%.*]]
; CHECK-NEXT: ret i1 [[SEL]]
;
%cmp1 = icmp ne i64 %x, 0
@@ -360,9 +359,8 @@ define i1 @test_select_inverse1(i64 %x, i1 %y) {
define i1 @test_select_inverse2(i64 %x, i1 %y) {
; CHECK-LABEL: @test_select_inverse2(
-; CHECK-NEXT: [[CMP1:%.*]] = icmp sgt i64 [[X:%.*]], -1
-; CHECK-NEXT: [[CMP2:%.*]] = icmp slt i64 [[X]], 0
-; CHECK-NEXT: [[SEL:%.*]] = select i1 [[Y:%.*]], i1 [[CMP1]], i1 [[CMP2]]
+; CHECK-NEXT: [[CMP2:%.*]] = icmp slt i64 [[X:%.*]], 0
+; CHECK-NEXT: [[SEL:%.*]] = xor i1 [[CMP2]], [[Y:%.*]]
; CHECK-NEXT: ret i1 [[SEL]]
;
%cmp1 = icmp sgt i64 %x, -1
@@ -373,9 +371,8 @@ define i1 @test_select_inverse2(i64 %x, i1 %y) {
define i1 @test_select_inverse3(ptr %x, i1 %y) {
; CHECK-LABEL: @test_select_inverse3(
-; CHECK-NEXT: [[CMP1:%.*]] = icmp eq ptr [[X:%.*]], null
-; CHECK-NEXT: [[CMP2:%.*]] = icmp ne ptr [[X]], null
-; CHECK-NEXT: [[SEL:%.*]] = select i1 [[Y:%.*]], i1 [[CMP1]], i1 [[CMP2]]
+; CHECK-NEXT: [[CMP2:%.*]] = icmp ne ptr [[X:%.*]], null
+; CHECK-NEXT: [[SEL:%.*]] = xor i1 [[CMP2]], [[Y:%.*]]
; CHECK-NEXT: ret i1 [[SEL]]
;
%cmp1 = icmp eq ptr %x, null
@@ -399,9 +396,8 @@ define i1 @test_select_inverse_fail(i64 %x, i1 %y) {
define <2 x i1> @test_select_inverse_vec(<2 x i64> %x, <2 x i1> %y) {
; CHECK-LABEL: @test_select_inverse_vec(
-; CHECK-NEXT: [[CMP1:%.*]] = icmp ne <2 x i64> [[X:%.*]], zeroinitializer
-; CHECK-NEXT: [[CMP2:%.*]] = icmp eq <2 x i64> [[X]], zeroinitializer
-; CHECK-NEXT: [[SEL:%.*]] = select <2 x i1> [[Y:%.*]], <2 x i1> [[CMP1]], <2 x i1> [[CMP2]]
+; CHECK-NEXT: [[CMP2:%.*]] = icmp eq <2 x i64> [[X:%.*]], zeroinitializer
+; CHECK-NEXT: [[SEL:%.*]] = xor <2 x i1> [[CMP2]], [[Y:%.*]]
; CHECK-NEXT: ret <2 x i1> [[SEL]]
;
%cmp1 = icmp ne <2 x i64> %x, zeroinitializer
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