https://gcc.gnu.org/g:205591919214cb5610e9c3b2394f05a3cfaa7f68

commit r15-5919-g205591919214cb5610e9c3b2394f05a3cfaa7f68
Author: Jakub Jelinek <ja...@redhat.com>
Date:   Wed Dec 4 10:54:41 2024 +0100

    c++: Fix up erroneous template error recovery ICE [PR117826]
    
    The testcase in the PR (which can't be easily reduced and is
    way too large and has way too many errors) results in an ICE,
    because the erroneous_templates hash_map holds trees of erroneous
    templates across ggc_collect and some of the templates in there
    could be removed, so the later lookup can crash on comparison of
    already freed and reused trees.
    
    The following patch makes the hash_map GTY((cache)) marked.
    The cp-tree.h changes before the erroneous_template declaration
    are needed to make gengtype happy, it didn't like using
    directive nor using a template-id as a template parameter.
    
    It is marked cache because if a decl would be solely referenced from
    the erroneous_templates hash_map, then nothing would look it up.
    
    2024-12-04  Jakub Jelinek  <ja...@redhat.com>
    
            PR c++/117826
            * cp-tree.h (struct decl_location_traits): New type.
            (erroneous_templates_t): Change using into typedef.
            (erroneous_templates): Add GTY((cache)).
            * error.cc (cp_adjust_diagnostic_info): Use
            hash_map_safe_get_or_insert<true> rather than
            hash_map_safe_get_or_insert<false> for erroneous_templates.

Diff:
---
 gcc/cp/cp-tree.h | 7 ++++---
 gcc/cp/error.cc  | 4 ++--
 2 files changed, 6 insertions(+), 5 deletions(-)

diff --git a/gcc/cp/cp-tree.h b/gcc/cp/cp-tree.h
index 0d6fce0f08b8..29f28d5e3833 100644
--- a/gcc/cp/cp-tree.h
+++ b/gcc/cp/cp-tree.h
@@ -7222,9 +7222,10 @@ extern location_t location_of                   (tree);
 extern void qualified_name_lookup_error                (tree, tree, tree,
                                                 location_t);
 
-using erroneous_templates_t
-  = hash_map<tree, location_t, simple_hashmap_traits<tree_decl_hash, 
location_t>>;
-extern erroneous_templates_t *erroneous_templates;
+struct decl_location_traits
+  : simple_cache_map_traits<tree_decl_hash, location_t> { };
+typedef hash_map<tree, location_t, decl_location_traits> erroneous_templates_t;
+extern GTY((cache)) erroneous_templates_t *erroneous_templates;
 
 extern bool cp_seen_error ();
 #define seen_error() cp_seen_error ()
diff --git a/gcc/cp/error.cc b/gcc/cp/error.cc
index 10d7f46346a8..ce8d5b15ac04 100644
--- a/gcc/cp/error.cc
+++ b/gcc/cp/error.cc
@@ -237,8 +237,8 @@ cp_adjust_diagnostic_info (diagnostic_context *context,
 
        bool existed;
        location_t &error_loc
-         = hash_map_safe_get_or_insert<false> (erroneous_templates,
-                                               tmpl, &existed);
+         = hash_map_safe_get_or_insert<true> (erroneous_templates,
+                                              tmpl, &existed);
        if (!existed)
          /* Remember that this template had a parse-time error so
             that we'll ensure a hard error has been issued upon

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