[gcc r16-9552] c++: Fix ICE during explanation of failed __has_unique_object_representation [PR126867]

https://gcc.gnu.org/g:5e7fa6dbae546cdc07857be19cf3aa2375e9edad

commit r16-9552-g5e7fa6dbae546cdc07857be19cf3aa2375e9edad
Author: Jakub Jelinek <[email protected]>
Date:   Tue Aug 18 20:15:45 2026 +0200

    c++: Fix ICE during explanation of failed __has_unique_object_representation [PR126867]
    
    The following testcase ICEs since r16-5520 added explain
    arguments to type_has_unique_obj_representations and
    record_has_unique_obj_representations.  Most of the location_t
    arguments in that change look correct, either DECL_SOURCE_LOCATION
    of some FIELD_DECL or in type_has_unique_obj_representations use
    loc, which is initialized to
      location_t loc = input_location;
      if (tree m = TYPE_MAIN_DECL (t))
        loc = DECL_SOURCE_LOCATION (m);
    But in record_has_unique_obj_representations we don't have
    a variable like that and t at that point is the RECORD_TYPE
    or UNION_TYPE, so using DECL_SOURCE_LOCATION on it will surely ICE
    in a checking compiler.
    location_of call does the above dances, so it seems easiest to
    call it rather than duplicate it by hand.
    
    2026-08-18  Jakub Jelinek  <[email protected]>
    
            PR c++/126867
            * tree.cc (record_has_unique_obj_representations): Use
            location_of (const_cast <tree> (t)) rather than
            DECL_SOURCE_LOCATION (t).
    
            * g++.dg/cpp1z/has-unique-obj-representations6.C: New test.
    
    Reviewed-by: Jason Merrill <[email protected]>
    (cherry picked from commit 318e6a4640420d5cc213df779bf751485fa56063)

Diff:
---
 gcc/cp/tree.cc                                               |  2 +-
 gcc/testsuite/g++.dg/cpp1z/has-unique-obj-representations6.C | 10 ++++++++++
 2 files changed, 11 insertions(+), 1 deletion(-)

diff --git a/gcc/cp/tree.cc b/gcc/cp/tree.cc
index f2ecc2df0d77..084dfd70f6bd 100644
--- a/gcc/cp/tree.cc
+++ b/gcc/cp/tree.cc
@@ -5247,7 +5247,7 @@ record_has_unique_obj_representations (const_tree t, const_tree sz,
 	    inform (DECL_SOURCE_LOCATION (last_named_field),
 		    "padding occurs after %qD", last_named_field);
 	  else
-	    inform (DECL_SOURCE_LOCATION (t),
+	    inform (location_of (const_cast <tree> (t)),
 		    "%qT has padding and no data fields", t);
 	}
       return false;
diff --git a/gcc/testsuite/g++.dg/cpp1z/has-unique-obj-representations6.C b/gcc/testsuite/g++.dg/cpp1z/has-unique-obj-representations6.C
new file mode 100644
index 000000000000..431b55ade522
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp1z/has-unique-obj-representations6.C
@@ -0,0 +1,10 @@
+// PR c++/126867
+// { dg-do compile { target c++17 } }
+
+template <class T>
+constexpr bool U = __has_unique_object_representations (T);
+
+struct S {};		// { dg-message "'S' does not have unique object representations, because" }
+			// { dg-message "'S' has padding and no data fields" "" { target *-*-* } .-1 }
+
+static_assert (U <S>);	// { dg-error "static assertion failed" }