[llvm] [InstCombine] Drop samesign in `foldLogOpOfMaskedICmps` (PR #125829)

[Yingwei Zheng via llvm-commits]

https://github.com/dtcxzyw created https://github.com/llvm/llvm-project/pull/125829

Alive2: https://alive2.llvm.org/ce/z/6zLAYp

Note: We can also apply this fix to the logic below (`if (Mask & AMask_NotAllOnes)`), but it seems unreachable.


>From feed257e9d1ea26cb65473679cfb482e1869557a Mon Sep 17 00:00:00 2001
From: Yingwei Zheng <dtcxzyw2333 at gmail.com>
Date: Wed, 5 Feb 2025 17:54:34 +0800
Subject: [PATCH 1/2] [InstCombine] Add pre-commit tests. NFC.

---
 .../InstCombine/sign-test-and-or.ll           | 23 +++++++++++++++++++
 1 file changed, 23 insertions(+)

diff --git a/llvm/test/Transforms/InstCombine/sign-test-and-or.ll b/llvm/test/Transforms/InstCombine/sign-test-and-or.ll
index 65363620563bed..a9d078e09447e1 100644
--- a/llvm/test/Transforms/InstCombine/sign-test-and-or.ll
+++ b/llvm/test/Transforms/InstCombine/sign-test-and-or.ll
@@ -349,6 +349,29 @@ define i1 @test9_logical(i32 %a) {
   ret i1 %or.cond
 }
 
+define i1 @test9_logical_samesign(i32 %a) {
+; CHECK-LABEL: @test9_logical_samesign(
+; CHECK-NEXT:    [[CMP2:%.*]] = icmp samesign sgt i32 [[A:%.*]], -1
+; CHECK-NEXT:    ret i1 [[CMP2]]
+;
+  %masked = and i32 %a, -1073741825
+  %cmp1 = icmp eq i32 %masked, 0
+  %cmp2 = icmp samesign sgt i32 %a, -1
+  %or.cond = select i1 %cmp1, i1 true, i1 %cmp2
+  ret i1 %or.cond
+}
+
+define i1 @test_logical_or_icmp_icmp_samesign(i32 %a) {
+; CHECK-LABEL: @test_logical_or_icmp_icmp_samesign(
+; CHECK-NEXT:    [[CMP2:%.*]] = icmp samesign sgt i32 [[A:%.*]], -1
+; CHECK-NEXT:    ret i1 [[CMP2]]
+;
+  %cmp1 = icmp eq i32 %a, 0
+  %cmp2 = icmp samesign sgt i32 %a, -1
+  %or = select i1 %cmp1, i1 true, i1 %cmp2
+  ret i1 %or
+}
+
 define i1 @test10(i32 %a) {
 ; CHECK-LABEL: @test10(
 ; CHECK-NEXT:    [[OR_COND:%.*]] = icmp ult i32 [[A:%.*]], 2

>From c9dc2952887ec78c549102bfdf64d55e12583548 Mon Sep 17 00:00:00 2001
From: Yingwei Zheng <dtcxzyw2333 at gmail.com>
Date: Wed, 5 Feb 2025 18:02:52 +0800
Subject: [PATCH 2/2] [InstCombine] Drop samesign in `foldLogOpOfMaskedICmps`

---
 llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp | 5 ++++-
 llvm/test/Transforms/InstCombine/sign-test-and-or.ll    | 4 ++--
 2 files changed, 6 insertions(+), 3 deletions(-)

diff --git a/llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp b/llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
index 8701f7c28a39fc..29f67f34a017ca 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
@@ -610,8 +610,11 @@ static Value *foldLogOpOfMaskedICmps(Value *LHS, Value *RHS, bool IsAnd,
       APInt NewMask = *ConstB & *ConstD;
       if (NewMask == *ConstB)
         return LHS;
-      if (NewMask == *ConstD)
+      if (NewMask == *ConstD) {
+        if (IsLogical)
+          cast<ICmpInst>(RHS)->setSameSign(false);
         return RHS;
+      }
     }
 
     if (Mask & AMask_NotAllOnes) {
diff --git a/llvm/test/Transforms/InstCombine/sign-test-and-or.ll b/llvm/test/Transforms/InstCombine/sign-test-and-or.ll
index a9d078e09447e1..3e9ff63869d646 100644
--- a/llvm/test/Transforms/InstCombine/sign-test-and-or.ll
+++ b/llvm/test/Transforms/InstCombine/sign-test-and-or.ll
@@ -351,7 +351,7 @@ define i1 @test9_logical(i32 %a) {
 
 define i1 @test9_logical_samesign(i32 %a) {
 ; CHECK-LABEL: @test9_logical_samesign(
-; CHECK-NEXT:    [[CMP2:%.*]] = icmp samesign sgt i32 [[A:%.*]], -1
+; CHECK-NEXT:    [[CMP2:%.*]] = icmp sgt i32 [[A:%.*]], -1
 ; CHECK-NEXT:    ret i1 [[CMP2]]
 ;
   %masked = and i32 %a, -1073741825
@@ -363,7 +363,7 @@ define i1 @test9_logical_samesign(i32 %a) {
 
 define i1 @test_logical_or_icmp_icmp_samesign(i32 %a) {
 ; CHECK-LABEL: @test_logical_or_icmp_icmp_samesign(
-; CHECK-NEXT:    [[CMP2:%.*]] = icmp samesign sgt i32 [[A:%.*]], -1
+; CHECK-NEXT:    [[CMP2:%.*]] = icmp sgt i32 [[A:%.*]], -1
 ; CHECK-NEXT:    ret i1 [[CMP2]]
 ;
   %cmp1 = icmp eq i32 %a, 0