[llvm] [FuncAttrs] Don't infer `noundef` for functions with `sanitize_memory` attribute (PR #76691)

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llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-llvm-transforms

Author: Yingwei Zheng (dtcxzyw)

<details>
<summary>Changes</summary>

MemorySanitizer assumes that the definition and declaration of a function will be consistent. If we add `noundef` for some definitions, it will break msan.

Fix buildbot failure caused by #<!-- -->76553.


---
Full diff: https://github.com/llvm/llvm-project/pull/76691.diff


2 Files Affected:

- (modified) llvm/lib/Transforms/IPO/FunctionAttrs.cpp (+6) 
- (modified) llvm/test/Transforms/FunctionAttrs/noundef.ll (+9) 


``````````diff
diff --git a/llvm/lib/Transforms/IPO/FunctionAttrs.cpp b/llvm/lib/Transforms/IPO/FunctionAttrs.cpp
index ce083979afc63a..7ebf265e17ba1f 100644
--- a/llvm/lib/Transforms/IPO/FunctionAttrs.cpp
+++ b/llvm/lib/Transforms/IPO/FunctionAttrs.cpp
@@ -1296,6 +1296,12 @@ static void addNoUndefAttrs(const SCCNodeSet &SCCNodes,
     if (!F->hasExactDefinition())
       return;
 
+    // MemorySanitizer assumes that the definition and declaration of a
+    // function will be consistent. A function with sanitize_memory attribute
+    // should be skipped from inference.
+    if (F->hasFnAttribute(Attribute::SanitizeMemory))
+      continue;
+
     if (F->getReturnType()->isVoidTy())
       continue;
 
diff --git a/llvm/test/Transforms/FunctionAttrs/noundef.ll b/llvm/test/Transforms/FunctionAttrs/noundef.ll
index b357587cc12394..946b562f39553e 100644
--- a/llvm/test/Transforms/FunctionAttrs/noundef.ll
+++ b/llvm/test/Transforms/FunctionAttrs/noundef.ll
@@ -143,3 +143,12 @@ define i32 @test_noundef_prop() {
   %ret = call i32 @test_ret_constant()
   ret i32 %ret
 }
+
+; Don't deduce noundef for functions with sanitize_memory.
+define i32 @test_ret_constant_msan() sanitize_memory {
+; CHECK-LABEL: define i32 @test_ret_constant_msan(
+; CHECK-SAME: ) #[[ATTR1:[0-9]+]] {
+; CHECK-NEXT:    ret i32 0
+;
+  ret i32 0
+}

``````````

</details>


https://github.com/llvm/llvm-project/pull/76691