[llvm] [CodeLayout] Fixing initialization of empty ranges (PR #68917)

[via llvm-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-llvm-transforms

Author: None (spupyrev)

<details>
<summary>Changes</summary>

Fixing libc++'s consistency checks, by eliminating ranges of singular iterators.

---
Full diff: https://github.com/llvm/llvm-project/pull/68917.diff


1 Files Affected:

- (modified) llvm/lib/Transforms/Utils/CodeLayout.cpp (+6-3) 


``````````diff
diff --git a/llvm/lib/Transforms/Utils/CodeLayout.cpp b/llvm/lib/Transforms/Utils/CodeLayout.cpp
index 057a5e86c04aca1..6a789e5187f1310 100644
--- a/llvm/lib/Transforms/Utils/CodeLayout.cpp
+++ b/llvm/lib/Transforms/Utils/CodeLayout.cpp
@@ -476,13 +476,16 @@ void ChainT::mergeEdges(ChainT *Other) {
 }
 
 using NodeIter = std::vector<NodeT *>::const_iterator;
+static std::vector<NodeT *> EmptyList;
 
 /// A wrapper around three chains of nodes; it is used to avoid extra
 /// instantiation of the vectors.
 struct MergedChain {
-  MergedChain(NodeIter Begin1, NodeIter End1, NodeIter Begin2 = NodeIter(),
-              NodeIter End2 = NodeIter(), NodeIter Begin3 = NodeIter(),
-              NodeIter End3 = NodeIter())
+  MergedChain(NodeIter Begin1, NodeIter End1,
+              NodeIter Begin2 = EmptyList.begin(),
+              NodeIter End2 = EmptyList.end(),
+              NodeIter Begin3 = EmptyList.begin(),
+              NodeIter End3 = EmptyList.end())
       : Begin1(Begin1), End1(End1), Begin2(Begin2), End2(End2), Begin3(Begin3),
         End3(End3) {}
 

``````````

</details>


https://github.com/llvm/llvm-project/pull/68917