[llvm] [InstCombine] Drop `samesign` flag in `foldAndOrOfICmpsWithConstEq` (PR #112489)

[via llvm-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-llvm-transforms

Author: Yingwei Zheng (dtcxzyw)

<details>
<summary>Changes</summary>

In https://github.com/llvm/llvm-project/commit/5dbfca30c1a672cd0c5089df2b4fdd171436643a we assume that RHS is poison implies LHS is also poison. It doesn't hold after introducing samesign flag.

This patch drops the `samesign` flag on RHS if the original expression is a logical and/or.

It is an alternative to https://github.com/llvm/llvm-project/pull/112475.
Closes #<!-- -->112467.


---
Full diff: https://github.com/llvm/llvm-project/pull/112489.diff


3 Files Affected:

- (modified) llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp (+7-1) 
- (modified) llvm/test/Transforms/InstCombine/and-or-icmp-min-max.ll (+11) 
- (modified) llvm/test/Transforms/InstCombine/and-or-icmp-nullptr.ll (+13) 


``````````diff
diff --git a/llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp b/llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
index 64bee4ab974ede..c8407e8ba5aba8 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
@@ -3369,8 +3369,14 @@ Value *InstCombinerImpl::foldAndOrOfICmps(ICmpInst *LHS, ICmpInst *RHS,
   // We can convert this case to bitwise and, because both operands are used
   // on the LHS, and as such poison from both will propagate.
   if (Value *V = foldAndOrOfICmpsWithConstEq(RHS, LHS, IsAnd,
-                                             /*IsLogical*/ false, Builder, Q))
+                                             /*IsLogical=*/false, Builder, Q)) {
+    // If RHS is still used, we should drop samesign flag.
+    if (IsLogical && RHS->hasSameSign() && !RHS->use_empty()) {
+      RHS->setSameSign(false);
+      addToWorklist(RHS);
+    }
     return V;
+  }
 
   if (Value *V = foldIsPowerOf2OrZero(LHS, RHS, IsAnd, Builder, *this))
     return V;
diff --git a/llvm/test/Transforms/InstCombine/and-or-icmp-min-max.ll b/llvm/test/Transforms/InstCombine/and-or-icmp-min-max.ll
index 058847a75bde7f..cc55c4a39a2678 100644
--- a/llvm/test/Transforms/InstCombine/and-or-icmp-min-max.ll
+++ b/llvm/test/Transforms/InstCombine/and-or-icmp-min-max.ll
@@ -689,6 +689,17 @@ define i1 @sge_and_max_logical(i8 %x, i8 %y)  {
   ret i1 %r
 }
 
+define i1 @sge_and_max_logical_samesign(i8 %x, i8 %y)  {
+; CHECK-LABEL: @sge_and_max_logical_samesign(
+; CHECK-NEXT:    [[CMPEQ:%.*]] = icmp eq i8 [[X:%.*]], 127
+; CHECK-NEXT:    ret i1 [[CMPEQ]]
+;
+  %cmp = icmp sge i8 %x, %y
+  %cmpeq = icmp samesign eq i8 %x, 127
+  %r = select i1 %cmp, i1 %cmpeq, i1 false
+  ret i1 %r
+}
+
 define i1 @sge_and_max_commute(i8 %x, i8 %y)  {
 ; CHECK-LABEL: @sge_and_max_commute(
 ; CHECK-NEXT:    [[CMPEQ:%.*]] = icmp eq i8 [[X:%.*]], 127
diff --git a/llvm/test/Transforms/InstCombine/and-or-icmp-nullptr.ll b/llvm/test/Transforms/InstCombine/and-or-icmp-nullptr.ll
index d533cc7048536c..8650b89c3b9ef3 100644
--- a/llvm/test/Transforms/InstCombine/and-or-icmp-nullptr.ll
+++ b/llvm/test/Transforms/InstCombine/and-or-icmp-nullptr.ll
@@ -592,6 +592,19 @@ define i1 @sgt_and_min_logical(ptr %x, ptr %y)  {
   ret i1 %r
 }
 
+define i1 @sgt_and_min_logical_samesign(ptr %x, ptr %y)  {
+; CHECK-LABEL: @sgt_and_min_logical_samesign(
+; CHECK-NEXT:    [[CMPEQ:%.*]] = icmp eq ptr [[X:%.*]], null
+; CHECK-NEXT:    [[TMP1:%.*]] = icmp slt ptr [[Y:%.*]], null
+; CHECK-NEXT:    [[R:%.*]] = and i1 [[CMPEQ]], [[TMP1]]
+; CHECK-NEXT:    ret i1 [[R]]
+;
+  %cmp = icmp sgt ptr %x, %y
+  %cmpeq = icmp samesign eq ptr %x, null
+  %r = select i1 %cmp, i1 %cmpeq, i1 false
+  ret i1 %r
+}
+
 define i1 @sle_or_not_min(ptr %x, ptr %y)  {
 ; CHECK-LABEL: @sle_or_not_min(
 ; CHECK-NEXT:    [[CMPEQ:%.*]] = icmp ne ptr [[X:%.*]], null

``````````

</details>


https://github.com/llvm/llvm-project/pull/112489