[llvm-branch-commits] [libcxx] 337beb7 - [libc++] Add _LIBCPP_NO_UNIQUE_ADDRESS to flat_{, multi}map::value_compare (#137594)

[Tom Stellard via llvm-branch-commits]

Author: Nikolas Klauser
Date: 2025-06-12T11:29:59-07:00
New Revision: 337beb73abfe05c2db1158f211042eb8763165ea

URL: https://github.com/llvm/llvm-project/commit/337beb73abfe05c2db1158f211042eb8763165ea
DIFF: https://github.com/llvm/llvm-project/commit/337beb73abfe05c2db1158f211042eb8763165ea.diff

LOG: [libc++] Add _LIBCPP_NO_UNIQUE_ADDRESS to flat_{,multi}map::value_compare (#137594)

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.

(cherry picked from commit ed0aa9961caa177098e9b7e69e98034d676f192e)

Added: 
    

Modified: 
    libcxx/include/__flat_map/flat_map.h
    libcxx/include/__flat_map/flat_multimap.h

Removed: 
    


################################################################################
diff  --git a/libcxx/include/__flat_map/flat_map.h b/libcxx/include/__flat_map/flat_map.h
index a0594ed9dc411..9cc39c0a1e067 100644
--- a/libcxx/include/__flat_map/flat_map.h
+++ b/libcxx/include/__flat_map/flat_map.h
@@ -113,7 +113,7 @@ 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;