[libcxx-commits] [libcxx] [libc++] Add _LIBCPP_NO_UNIQUE_ADDRESS to flat_{, multi}map::value_compare (PR #137594)

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llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-libcxx

Author: Nikolas Klauser (philnik777)

<details>
<summary>Changes</summary>

This breaks the ABI of `flat_{,multi}map::value_compare`, but this type has only been introduced in LLVM 20, so it should be very unlikely that we break anybody if we back-port this now.


---
Full diff: https://github.com/llvm/llvm-project/pull/137594.diff


2 Files Affected:

- (modified) libcxx/include/__flat_map/flat_map.h (+1-1) 
- (modified) libcxx/include/__flat_map/flat_multimap.h (+1-1) 


``````````diff
diff --git a/libcxx/include/__flat_map/flat_map.h b/libcxx/include/__flat_map/flat_map.h
index f5abfd0985280..f5e9756ff6a60 100644
--- a/libcxx/include/__flat_map/flat_map.h
+++ b/libcxx/include/__flat_map/flat_map.h
@@ -114,7 +114,7 @@ class flat_map {
 
   class value_compare {
   private:
-    key_compare __comp_;
+    _LIBCPP_NO_UNIQUE_ADDRESS key_compare __comp_;
     _LIBCPP_HIDE_FROM_ABI value_compare(key_compare __c) : __comp_(__c) {}
     friend flat_map;
 
diff --git a/libcxx/include/__flat_map/flat_multimap.h b/libcxx/include/__flat_map/flat_multimap.h
index ea77fb5d79bd2..15fcd7995ad0a 100644
--- a/libcxx/include/__flat_map/flat_multimap.h
+++ b/libcxx/include/__flat_map/flat_multimap.h
@@ -115,7 +115,7 @@ class flat_multimap {
 
   class value_compare {
   private:
-    key_compare __comp_;
+    _LIBCPP_NO_UNIQUE_ADDRESS key_compare __comp_;
     _LIBCPP_HIDE_FROM_ABI value_compare(key_compare __c) : __comp_(__c) {}
     friend flat_multimap;
 

``````````

</details>


https://github.com/llvm/llvm-project/pull/137594