[llvm] [InstCombine] Fold `X!=Y ? ctz(X^Y, true) : BW -> ctz(X^Y, false)` (PR #128483)
Yingwei Zheng via llvm-commits
llvm-commits at lists.llvm.org
Mon Feb 24 00:49:28 PST 2025
https://github.com/dtcxzyw created https://github.com/llvm/llvm-project/pull/128483
Proof: https://alive2.llvm.org/ce/z/mzL6W2
Closes https://github.com/llvm/llvm-project/issues/128441.
>From ec4fa8452a04acca48d516a9a4088c241a601f12 Mon Sep 17 00:00:00 2001
From: Yingwei Zheng <dtcxzyw2333 at gmail.com>
Date: Mon, 24 Feb 2025 16:32:26 +0800
Subject: [PATCH 1/3] [InstCombine] Add pre-commit tests. NFC.
---
.../InstCombine/select-cmp-cttz-ctlz.ll | 67 +++++++++++++++++++
1 file changed, 67 insertions(+)
diff --git a/llvm/test/Transforms/InstCombine/select-cmp-cttz-ctlz.ll b/llvm/test/Transforms/InstCombine/select-cmp-cttz-ctlz.ll
index 2cb70e85f435f..16afd84e2019e 100644
--- a/llvm/test/Transforms/InstCombine/select-cmp-cttz-ctlz.ll
+++ b/llvm/test/Transforms/InstCombine/select-cmp-cttz-ctlz.ll
@@ -657,6 +657,73 @@ define i16 @test_multiuse_trunc_undef(i64 %x, ptr %p) {
ret i16 %cond
}
+define i64 @test_pr128441(i64 %x, i64 %y) {
+; CHECK-LABEL: @test_pr128441(
+; CHECK-NEXT: [[ISZERO_NOT:%.*]] = icmp eq i64 [[X:%.*]], [[Y:%.*]]
+; CHECK-NEXT: [[XOR:%.*]] = xor i64 [[X]], [[Y]]
+; CHECK-NEXT: [[CTTZ:%.*]] = call range(i64 0, 65) i64 @llvm.cttz.i64(i64 [[XOR]], i1 true)
+; CHECK-NEXT: [[SEL:%.*]] = select i1 [[ISZERO_NOT]], i64 64, i64 [[CTTZ]]
+; CHECK-NEXT: ret i64 [[SEL]]
+;
+ %iszero = icmp ne i64 %x, %y
+ %xor = xor i64 %x, %y
+ %cttz = call i64 @llvm.cttz.i64(i64 %xor, i1 true)
+ %sel = select i1 %iszero, i64 %cttz, i64 64
+ ret i64 %sel
+}
+
+define i64 @test_pr128441_commuted1(i64 %x, i64 %y) {
+; CHECK-LABEL: @test_pr128441_commuted1(
+; CHECK-NEXT: [[ISZERO_NOT:%.*]] = icmp eq i64 [[X:%.*]], [[Y:%.*]]
+; CHECK-NEXT: [[XOR:%.*]] = xor i64 [[Y]], [[X]]
+; CHECK-NEXT: [[CTTZ:%.*]] = call range(i64 0, 65) i64 @llvm.cttz.i64(i64 [[XOR]], i1 true)
+; CHECK-NEXT: [[SEL:%.*]] = select i1 [[ISZERO_NOT]], i64 64, i64 [[CTTZ]]
+; CHECK-NEXT: ret i64 [[SEL]]
+;
+ %iszero = icmp ne i64 %x, %y
+ %xor = xor i64 %y, %x
+ %cttz = call i64 @llvm.cttz.i64(i64 %xor, i1 true)
+ %sel = select i1 %iszero, i64 %cttz, i64 64
+ ret i64 %sel
+}
+
+define i64 @test_pr128441_commuted2(i64 %x, i64 %y) {
+; CHECK-LABEL: @test_pr128441_commuted2(
+; CHECK-NEXT: [[ISZERO:%.*]] = icmp eq i64 [[X:%.*]], [[Y:%.*]]
+; CHECK-NEXT: [[XOR:%.*]] = xor i64 [[X]], [[Y]]
+; CHECK-NEXT: [[CTTZ:%.*]] = call range(i64 0, 65) i64 @llvm.cttz.i64(i64 [[XOR]], i1 true)
+; CHECK-NEXT: [[SEL:%.*]] = select i1 [[ISZERO]], i64 64, i64 [[CTTZ]]
+; CHECK-NEXT: ret i64 [[SEL]]
+;
+ %iszero = icmp eq i64 %x, %y
+ %xor = xor i64 %x, %y
+ %cttz = call i64 @llvm.cttz.i64(i64 %xor, i1 true)
+ %sel = select i1 %iszero, i64 64, i64 %cttz
+ ret i64 %sel
+}
+
+define i64 @test_pr128441_commuted3_negative(i64 %x, i64 %y) {
+; CHECK-LABEL: @test_pr128441_commuted3_negative(
+; CHECK-NEXT: ret i64 64
+;
+ %iszero = icmp eq i64 %x, %y
+ %xor = xor i64 %y, %x
+ %cttz = call i64 @llvm.cttz.i64(i64 %xor, i1 true)
+ %sel = select i1 %iszero, i64 %cttz, i64 64
+ ret i64 %sel
+}
+
+define i64 @test_pr128441_commuted4_negative(i64 %x, i64 %y) {
+; CHECK-LABEL: @test_pr128441_commuted4_negative(
+; CHECK-NEXT: ret i64 64
+;
+ %iszero = icmp ne i64 %x, %y
+ %xor = xor i64 %x, %y
+ %cttz = call i64 @llvm.cttz.i64(i64 %xor, i1 true)
+ %sel = select i1 %iszero, i64 64, i64 %cttz
+ ret i64 %sel
+}
+
declare i16 @llvm.ctlz.i16(i16, i1)
declare i32 @llvm.ctlz.i32(i32, i1)
declare i64 @llvm.ctlz.i64(i64, i1)
>From 546ea60dde501221231ebc75f2d4da1043f74fac Mon Sep 17 00:00:00 2001
From: Yingwei Zheng <dtcxzyw2333 at gmail.com>
Date: Mon, 24 Feb 2025 16:33:17 +0800
Subject: [PATCH 2/3] [InstCombine] Fold `X!=Y ? ctz(X^Y,true) : BW ->
ctz(X^Y,false)`
---
.../InstCombine/InstCombineSelect.cpp | 6 ++++--
.../InstCombine/select-cmp-cttz-ctlz.ll | 18 ++++++------------
2 files changed, 10 insertions(+), 14 deletions(-)
diff --git a/llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp b/llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp
index e621a0b7fe596..1af0613690899 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp
@@ -1227,8 +1227,10 @@ static Value *foldSelectCttzCtlz(ICmpInst *ICI, Value *TrueVal, Value *FalseVal,
// (X == 0) ? BitWidth : ctz(X)
// (X == -1) ? BitWidth : ctz(~X)
- if ((X != CmpLHS || !match(CmpRHS, m_Zero())) &&
- (!match(X, m_Not(m_Specific(CmpLHS))) || !match(CmpRHS, m_AllOnes())))
+ // (X == Y) ? BitWidth : ctz(X ^ Y)
+ if (!(X == CmpLHS && match(CmpRHS, m_Zero())) &&
+ !(match(X, m_Not(m_Specific(CmpLHS))) && match(CmpRHS, m_AllOnes())) &&
+ !match(X, m_c_Xor(m_Specific(CmpLHS), m_Specific(CmpRHS))))
return nullptr;
IntrinsicInst *II = cast<IntrinsicInst>(Count);
diff --git a/llvm/test/Transforms/InstCombine/select-cmp-cttz-ctlz.ll b/llvm/test/Transforms/InstCombine/select-cmp-cttz-ctlz.ll
index 16afd84e2019e..52a32e19f57ef 100644
--- a/llvm/test/Transforms/InstCombine/select-cmp-cttz-ctlz.ll
+++ b/llvm/test/Transforms/InstCombine/select-cmp-cttz-ctlz.ll
@@ -659,10 +659,8 @@ define i16 @test_multiuse_trunc_undef(i64 %x, ptr %p) {
define i64 @test_pr128441(i64 %x, i64 %y) {
; CHECK-LABEL: @test_pr128441(
-; CHECK-NEXT: [[ISZERO_NOT:%.*]] = icmp eq i64 [[X:%.*]], [[Y:%.*]]
-; CHECK-NEXT: [[XOR:%.*]] = xor i64 [[X]], [[Y]]
-; CHECK-NEXT: [[CTTZ:%.*]] = call range(i64 0, 65) i64 @llvm.cttz.i64(i64 [[XOR]], i1 true)
-; CHECK-NEXT: [[SEL:%.*]] = select i1 [[ISZERO_NOT]], i64 64, i64 [[CTTZ]]
+; CHECK-NEXT: [[XOR:%.*]] = xor i64 [[X:%.*]], [[Y:%.*]]
+; CHECK-NEXT: [[SEL:%.*]] = call range(i64 0, 65) i64 @llvm.cttz.i64(i64 [[XOR]], i1 false)
; CHECK-NEXT: ret i64 [[SEL]]
;
%iszero = icmp ne i64 %x, %y
@@ -674,10 +672,8 @@ define i64 @test_pr128441(i64 %x, i64 %y) {
define i64 @test_pr128441_commuted1(i64 %x, i64 %y) {
; CHECK-LABEL: @test_pr128441_commuted1(
-; CHECK-NEXT: [[ISZERO_NOT:%.*]] = icmp eq i64 [[X:%.*]], [[Y:%.*]]
-; CHECK-NEXT: [[XOR:%.*]] = xor i64 [[Y]], [[X]]
-; CHECK-NEXT: [[CTTZ:%.*]] = call range(i64 0, 65) i64 @llvm.cttz.i64(i64 [[XOR]], i1 true)
-; CHECK-NEXT: [[SEL:%.*]] = select i1 [[ISZERO_NOT]], i64 64, i64 [[CTTZ]]
+; CHECK-NEXT: [[XOR:%.*]] = xor i64 [[Y:%.*]], [[X:%.*]]
+; CHECK-NEXT: [[SEL:%.*]] = call range(i64 0, 65) i64 @llvm.cttz.i64(i64 [[XOR]], i1 false)
; CHECK-NEXT: ret i64 [[SEL]]
;
%iszero = icmp ne i64 %x, %y
@@ -689,10 +685,8 @@ define i64 @test_pr128441_commuted1(i64 %x, i64 %y) {
define i64 @test_pr128441_commuted2(i64 %x, i64 %y) {
; CHECK-LABEL: @test_pr128441_commuted2(
-; CHECK-NEXT: [[ISZERO:%.*]] = icmp eq i64 [[X:%.*]], [[Y:%.*]]
-; CHECK-NEXT: [[XOR:%.*]] = xor i64 [[X]], [[Y]]
-; CHECK-NEXT: [[CTTZ:%.*]] = call range(i64 0, 65) i64 @llvm.cttz.i64(i64 [[XOR]], i1 true)
-; CHECK-NEXT: [[SEL:%.*]] = select i1 [[ISZERO]], i64 64, i64 [[CTTZ]]
+; CHECK-NEXT: [[XOR:%.*]] = xor i64 [[X:%.*]], [[Y:%.*]]
+; CHECK-NEXT: [[SEL:%.*]] = call range(i64 0, 65) i64 @llvm.cttz.i64(i64 [[XOR]], i1 false)
; CHECK-NEXT: ret i64 [[SEL]]
;
%iszero = icmp eq i64 %x, %y
>From 694e03e54ceceaf08898e645aa42674f1a061bae Mon Sep 17 00:00:00 2001
From: Yingwei Zheng <dtcxzyw2333 at gmail.com>
Date: Mon, 24 Feb 2025 16:42:45 +0800
Subject: [PATCH 3/3] [InstCombine] Revert nfc chagnes
---
llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp b/llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp
index 1af0613690899..dca969e160bb7 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp
@@ -1228,8 +1228,8 @@ static Value *foldSelectCttzCtlz(ICmpInst *ICI, Value *TrueVal, Value *FalseVal,
// (X == 0) ? BitWidth : ctz(X)
// (X == -1) ? BitWidth : ctz(~X)
// (X == Y) ? BitWidth : ctz(X ^ Y)
- if (!(X == CmpLHS && match(CmpRHS, m_Zero())) &&
- !(match(X, m_Not(m_Specific(CmpLHS))) && match(CmpRHS, m_AllOnes())) &&
+ if ((X != CmpLHS || !match(CmpRHS, m_Zero())) &&
+ (!match(X, m_Not(m_Specific(CmpLHS))) || !match(CmpRHS, m_AllOnes())) &&
!match(X, m_c_Xor(m_Specific(CmpLHS), m_Specific(CmpRHS))))
return nullptr;
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