[llvm] MemoryDependenceAnalysis: Consider a pointer clobbered if it is saved (PR #142096)

[via llvm-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-llvm-analysis

Author: YunQiang Su (wzssyqa)

<details>
<summary>Changes</summary>

In MemoryDependenceResults::getSimplePointerDependencyFrom, when we find the instruction that a LoadInst depends, if we find an store instruction that save the pointer used by LoadInst, we consider the pointer may be clobbered.

---
Full diff: https://github.com/llvm/llvm-project/pull/142096.diff


1 Files Affected:

- (modified) llvm/lib/Analysis/MemoryDependenceAnalysis.cpp (+5) 


``````````diff
diff --git a/llvm/lib/Analysis/MemoryDependenceAnalysis.cpp b/llvm/lib/Analysis/MemoryDependenceAnalysis.cpp
index f062189bac6a0..00f36b9e088ad 100644
--- a/llvm/lib/Analysis/MemoryDependenceAnalysis.cpp
+++ b/llvm/lib/Analysis/MemoryDependenceAnalysis.cpp
@@ -564,6 +564,11 @@ MemDepResult MemoryDependenceResults::getSimplePointerDependencyFrom(
         if (!QueryInst || QueryInst->isVolatile())
           return MemDepResult::getClobber(SI);
 
+      // If we store the pointer of QueryInst, it is danger due to that the address
+      // may be modified with other reference.
+      if (QueryInst && QueryInst->getOperand(0) == SI->getOperand(0))
+        return MemDepResult::getClobber(SI);
+
       // If alias analysis can tell that this store is guaranteed to not modify
       // the query pointer, ignore it.  Use getModRefInfo to handle cases where
       // the query pointer points to constant memory etc.

``````````

</details>


https://github.com/llvm/llvm-project/pull/142096