[C++ Patch] PR 71464 ("[6/7/8 Regression] ICE on invalid code (with redeclared constructor) at -Os: Segmentation fault")

[Paolo Carlini]

Hi,

this error recovery ICE happens only with -Os and is just a P5 - on the 
other hand I would argue the reproducer isn't that exotic! - but seems 
fixable easily and safely: cdtor_comdat_group immediately calls 
DECL_ASSEMBLER_NAME on both arguments and of course crashes if they are 
null. Tested x86_64-linux.

Thanks, Paolo.

//////////////////

/cp
2018-03-02  Paolo Carlini  <paolo.carl...@oracle.com>

        PR c++/71464
        * optimize.c (maybe_thunk_body): When HAVE_COMDAT_GROUP is true,
        bail out immediately if either fns[1] or fns[0] is null.

/testsuite
2018-03-02  Paolo Carlini  <paolo.carl...@oracle.com>

        PR c++/71464
        * g++.dg/torture/pr71464.C: New.
Index: cp/optimize.c
===================================================================
--- cp/optimize.c       (revision 258151)
+++ cp/optimize.c       (working copy)
@@ -276,6 +276,9 @@ maybe_thunk_body (tree fn, bool force)
     {
       /* At eof, defer creation of mangling aliases temporarily.  */
       bool save_defer_mangling_aliases = defer_mangling_aliases;
+      if (!fns[1] || !fns[0])
+       /* Can happen during error recovery (c++/71464).  */
+       return 0;
       defer_mangling_aliases = true;
       tree comdat_group = cdtor_comdat_group (fns[1], fns[0]);
       defer_mangling_aliases = save_defer_mangling_aliases;
Index: testsuite/g++.dg/torture/pr71464.C
===================================================================
--- testsuite/g++.dg/torture/pr71464.C  (nonexistent)
+++ testsuite/g++.dg/torture/pr71464.C  (working copy)
@@ -0,0 +1,7 @@
+struct A {}; 
+
+struct B : virtual A
+{
+  B () {};
+  B () {};  // { dg-error "cannot be overloaded" }
+};