[PATCH] c++: Fix ICE with -Wmismatched-tags [PR93869]

[Marek Polacek]

This is a crash in cp_parser_check_class_key:
  tree type_decl = TYPE_MAIN_DECL (type);
  tree name = DECL_NAME (type_decl); // HERE
because TYPE_MAIN_DECL of type was null as it's not a class type.
Instead of checking CLASS_TYPE_P we should simply check class_key
a bit earlier (in this case it was typename_type).

Bootstrapped/regtested on x86_64-linux, ok for trunk?

2020-02-21  Marek Polacek  <pola...@redhat.com>

        PR c++/93869 - ICE with -Wmismatched-tags.
        * parser.c (cp_parser_check_class_key): Check class_key earlier.

        * g++.dg/warn/Wmismatched-tags-2.C: New test.
---
 gcc/cp/parser.c                                | 14 +++++++-------
 gcc/testsuite/g++.dg/warn/Wmismatched-tags-2.C |  6 ++++++
 2 files changed, 13 insertions(+), 7 deletions(-)
 create mode 100644 gcc/testsuite/g++.dg/warn/Wmismatched-tags-2.C

diff --git a/gcc/cp/parser.c b/gcc/cp/parser.c
index ee534b5db21..d5f2c14d951 100644
--- a/gcc/cp/parser.c
+++ b/gcc/cp/parser.c
@@ -30987,6 +30987,13 @@ cp_parser_check_class_key (cp_parser *parser, 
location_t key_loc,
   if (!warn_mismatched_tags && !warn_redundant_tags)
     return;
 
+  /* Only consider the true class-keys below and ignore typename_type,
+     etc. that are not C++ class-keys.  */
+  if (class_key != class_type
+      && class_key != record_type
+      && class_key != union_type)
+    return;
+
   tree type_decl = TYPE_MAIN_DECL (type);
   tree name = DECL_NAME (type_decl);
   /* Look up the NAME to see if it unambiguously refers to the TYPE
@@ -30995,13 +31002,6 @@ cp_parser_check_class_key (cp_parser *parser, 
location_t key_loc,
   tree decl = cp_parser_lookup_name_simple (parser, name, input_location);
   pop_deferring_access_checks ();
 
-  /* Only consider the true class-keys below and ignore typename_type,
-     etc. that are not C++ class-keys.  */
-  if (class_key != class_type
-      && class_key != record_type
-      && class_key != union_type)
-    return;
-
   /* The class-key is redundant for uses of the CLASS_TYPE that are
      neither definitions of it nor declarations, and for which name
      lookup returns just the type itself.  */
diff --git a/gcc/testsuite/g++.dg/warn/Wmismatched-tags-2.C 
b/gcc/testsuite/g++.dg/warn/Wmismatched-tags-2.C
new file mode 100644
index 00000000000..00193f02f61
--- /dev/null
+++ b/gcc/testsuite/g++.dg/warn/Wmismatched-tags-2.C
@@ -0,0 +1,6 @@
+// PR c++/93869 - ICE with -Wmismatched-tags.
+// { dg-do compile }
+// { dg-options "-Wmismatched-tags" }
+
+namespace N { typedef int T; }
+typename N::T x;

base-commit: dbfba41e95d1d93b17e907b7f516b52ed3a3c415
-- 
Marek Polacek • Red Hat, Inc. • 300 A St, Boston, MA