[llvm] [llvm] Avoid out-of-order evaluation in DebugInfo (PR #125116)

[via llvm-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-debuginfo

Author: Elvin Wang (elvinw-intel)

<details>
<summary>Changes</summary>

This is an upstream proposal from https://github.com/intel/intel-graphics-compiler/commit/e60884cb98c4332a0eecff8396eb353c5b86cd35 
We observed malfunctioning StripNonLineTableDebugInfo during debugging and it's caused by out-of-order evaluation, this is a C++ level semantic ambiguity issue, refer https://en.cppreference.com/w/cpp/language/eval_order
Solution is simply separating one line into two.

---
Full diff: https://github.com/llvm/llvm-project/pull/125116.diff


1 Files Affected:

- (modified) llvm/lib/IR/DebugInfo.cpp (+5-1) 


``````````diff
diff --git a/llvm/lib/IR/DebugInfo.cpp b/llvm/lib/IR/DebugInfo.cpp
index 4ce518009bd3ea..ea1d79d436041f 100644
--- a/llvm/lib/IR/DebugInfo.cpp
+++ b/llvm/lib/IR/DebugInfo.cpp
@@ -798,7 +798,11 @@ class DebugTypeInfoRemoval {
 
       return getReplacementMDNode(N);
     };
-    Replacements[N] = doRemap(N);
+    // Seperate recursive doRemap and operator [] into 2 lines to avoid
+    // out-of-order evaluations since both of them can access the same memory
+    // location in map Replacements.
+    auto Value = doRemap(N);
+    Replacements[N] = Value;
   }
 
   /// Do the remapping traversal.

``````````

</details>


https://github.com/llvm/llvm-project/pull/125116