[llvm] [InstCombine] Drop poison generating flags on Or in simplifyAssocCastAssoc. (PR #74763)

[via llvm-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-llvm-transforms

Author: Craig Topper (topperc)

<details>
<summary>Changes</summary>

Fixes #<!-- -->74739.

---
Full diff: https://github.com/llvm/llvm-project/pull/74763.diff


2 Files Affected:

- (modified) llvm/lib/Transforms/InstCombine/InstructionCombining.cpp (+1) 
- (modified) llvm/test/Transforms/InstCombine/or.ll (+13) 


``````````diff
diff --git a/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp b/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
index 30e058000d2bc..f072f5cec3094 100644
--- a/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
@@ -356,6 +356,7 @@ static bool simplifyAssocCastAssoc(BinaryOperator *BinOp1,
 
   IC.replaceOperand(*Cast, 0, BinOp2->getOperand(0));
   IC.replaceOperand(*BinOp1, 1, FoldedC);
+  BinOp1->dropPoisonGeneratingFlags();
   Cast->dropPoisonGeneratingFlags();
   return true;
 }
diff --git a/llvm/test/Transforms/InstCombine/or.ll b/llvm/test/Transforms/InstCombine/or.ll
index fd415682b67f3..8c8aab2bcba6a 100644
--- a/llvm/test/Transforms/InstCombine/or.ll
+++ b/llvm/test/Transforms/InstCombine/or.ll
@@ -1608,3 +1608,16 @@ define i8 @drop_disjoint(i8 %x) {
   %b = or disjoint i8 %a, 1
   ret i8 %b
 }
+
+; Make sure we drop disjoint when combining the Ors.
+define i32 @assoc_cast_assoc_disjoint(i16 %x) {
+; CHECK-LABEL: @assoc_cast_assoc_disjoint(
+; CHECK-NEXT:    [[B:%.*]] = zext i16 [[X:%.*]] to i32
+; CHECK-NEXT:    [[C:%.*]] = or i32 [[B]], 65537
+; CHECK-NEXT:    ret i32 [[C]]
+;
+  %a = or i16 %x, 1
+  %b = zext i16 %a to i32
+  %c = or disjoint i32 %b, 65536
+  ret i32 %c
+}

``````````

</details>


https://github.com/llvm/llvm-project/pull/74763