[llvm] Fix potential Out-of-order Evaluation in DebugInfo

[NaiveWang]

In DebugTypeInfoRemoval, DenseMap Replacements's assignment's rvalue is a recursive function that may access Replacements itself. Since C++17 such an "right to left" order cannot get guaranteed. This change is to separate 1 line into 2, avoid such a case.

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[llvmbot]

@llvm/pr-subscribers-debuginfo

@llvm/pr-subscribers-llvm-ir

Author: Elvin Wang (NaiveWang)

Changes

In DebugTypeInfoRemoval, DenseMap Replacements's assignment's rvalue is a recursive function that may access Replacements itself. Since C++17 such an "right to left" order cannot get guaranteed. This change is to separate 1 line into 2, avoid such a case.

---

Full diff: https://github.com/llvm/llvm-project/pull/124385.diff

1 Files Affected:

• (modified) llvm/lib/IR/DebugInfo.cpp (+2-1)

diff --git a/llvm/lib/IR/DebugInfo.cpp b/llvm/lib/IR/DebugInfo.cpp
index 4ce518009bd3ea..f4080ce532ef38 100644
--- a/llvm/lib/IR/DebugInfo.cpp
+++ b/llvm/lib/IR/DebugInfo.cpp
@@ -798,7 +798,8 @@ class DebugTypeInfoRemoval {
 
       return getReplacementMDNode(N);
     };
-    Replacements[N] = doRemap(N);
+    auto value = doRemap(N);
+    Replacements[N] = value;
   }
 
   /// Do the remapping traversal.

[dwblaikie]

Perhaps add a comment so someone doesn't undo this too easily in the future?

[dwblaikie]

In the comment, maybe clarify that doRemap can recurse back into remap (& so modify Replacements, etc)

[NaiveWang]

@dwblaikie I will draft another formal upstream patch using corp account when everything's ready, thanks for the review, closing this one.