[gcc r15-3744] c++: CWG 2789 and reversed operator candidates

[Patrick Palka via Gcc-cvs]

https://gcc.gnu.org/g:1f70503232d4183b4b58f2910c460569d05907b9

commit r15-3744-g1f70503232d4183b4b58f2910c460569d05907b9
Author: Patrick Palka <ppa...@redhat.com>
Date:   Fri Sep 20 15:41:42 2024 -0400

    c++: CWG 2789 and reversed operator candidates
    
    As a follow-up to r15-3741-gee3efe06c9c49c, which was specifically
    concerned with usings, it seems the CWG 2789 refinement should also
    compare contexts of a reversed vs non-reversed (member) candidate
    during operator overload resolution.
    
            DR 2789
    
    gcc/cp/ChangeLog:
    
            * call.cc (cand_parms_match): Check for matching class contexts
            even in the reversed case.
    
    gcc/testsuite/ChangeLog:
    
            * g++.dg/cpp2a/concepts-memfun4.C: Adjust expected result
            involving reversed candidate.
    
    Reviewed-by: Jason Merrill <ja...@redhat.com>

Diff:
---
 gcc/cp/call.cc                                | 11 +++++++----
 gcc/testsuite/g++.dg/cpp2a/concepts-memfun4.C |  6 +++---
 2 files changed, 10 insertions(+), 7 deletions(-)

diff --git a/gcc/cp/call.cc b/gcc/cp/call.cc
index f2ce50857ece..70783baac242 100644
--- a/gcc/cp/call.cc
+++ b/gcc/cp/call.cc
@@ -12865,10 +12865,6 @@ cand_parms_match (z_candidate *c1, z_candidate *c2, 
pmatch match_kind)
        }
     }
 
-  else if (reversed)
-    return (reversed_match (c1, c2)
-           && reversed_match (c2, c1));
-
   tree parms1 = TYPE_ARG_TYPES (TREE_TYPE (fn1));
   tree parms2 = TYPE_ARG_TYPES (TREE_TYPE (fn2));
 
@@ -12880,6 +12876,10 @@ cand_parms_match (z_candidate *c1, z_candidate *c2, 
pmatch match_kind)
       if (base1 != base2)
        return false;
 
+      if (reversed)
+       return (reversed_match (c1, c2)
+               && reversed_match (c2, c1));
+
       /* Use object_parms_correspond to simplify comparing iobj/xobj/static
         member functions.  */
       if (!object_parms_correspond (fn1, fn2, base1))
@@ -12897,6 +12897,9 @@ cand_parms_match (z_candidate *c1, z_candidate *c2, 
pmatch match_kind)
       parms1 = skip_parms (fn1, parms1);
       parms2 = skip_parms (fn2, parms2);
     }
+  else if (reversed)
+    return (reversed_match (c1, c2)
+           && reversed_match (c2, c1));
   return compparms (parms1, parms2);
 }
 
diff --git a/gcc/testsuite/g++.dg/cpp2a/concepts-memfun4.C 
b/gcc/testsuite/g++.dg/cpp2a/concepts-memfun4.C
index cf7f13c007d1..d849e9129a3b 100644
--- a/gcc/testsuite/g++.dg/cpp2a/concepts-memfun4.C
+++ b/gcc/testsuite/g++.dg/cpp2a/concepts-memfun4.C
@@ -91,7 +91,7 @@ namespace N1 {
 
   A<> a;
   B<> b;
-  // when comparing the A op== to the reversed B op==, we compare them in
-  // reverse order, so they match, and we choose the more constrained.
-  static_assert (a == b);
+  // A op== and B op== are defined in different classes so constraints
+  // aren't considered, and the tie is broken via reversedness.
+  static_assert (!(a == b));
 }