[google/gcc-4_7, trunk] Fix problem with -fdebug-types-section and template instantiations

[Cary Coutant]

This patch is for trunk and the google/gcc-4_7 branch.

When a class template instantiation is moved into a separate type unit,
it can bring along a lot of other referenced types into the type unit,
especially if the template is derived from another (large) type that
does not have an actually have a type definition in a type unit of its
own. When there are many instantiations of the same template, we get
a lot of duplication, and in the worst case (a template with several
parameters, instantiated multiple times along each dimension), GCC
can end up taking a long time and exhausting available memory. Because
instantiations typically happen in .cc files, and the resulting type
definition is unlikely to be useful as a comdat type unit, this patch
avoids the problem by choosing not to move template instantiations
into type units.

Bootstraps and passes regression tests. Also tested with a large
internal test case that previously resulted in out-of-memory during
compilation.

Google ref b/7041390.


2012-08-25   Cary Coutant  <ccout...@google.com>

gcc/
        * dwarf2out.c (is_template_instantiation): New function.
        (should_move_die_to_comdat): Reject types that are template
        instantiations.


Index: gcc/dwarf2out.c
===================================================================
--- gcc/dwarf2out.c     (revision 190681)
+++ gcc/dwarf2out.c     (working copy)
@@ -7277,6 +7277,21 @@ contains_subprogram_definition (dw_die_r
   return 0;
 }
 
+/* Return non-zero if this DIE represents a template instantiation.  */
+
+static int
+is_template_instantiation (dw_die_ref die)
+{
+  dw_die_ref c;
+
+  FOR_EACH_CHILD (die, c,
+                 if (c->die_tag == DW_TAG_template_type_param
+                     || c->die_tag == DW_TAG_template_value_param
+                     || c->die_tag == DW_TAG_GNU_template_template_param)
+                   return 1);
+  return 0;
+}
+
 /* Return non-zero if this is a type DIE that should be moved to a
    COMDAT .debug_types section.  */
 
@@ -7294,6 +7309,7 @@ should_move_die_to_comdat (dw_die_ref di
       if (is_declaration_die (die)
           || get_AT (die, DW_AT_abstract_origin)
           || is_nested_in_subprogram (die)
+         || is_template_instantiation (die)
          || contains_subprogram_definition (die))
         return 0;
       return 1;