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Re: varpool alias reorg
> On Sat, Jun 18, 2011 at 7:19 AM, H.J. Lu <hjl.tools@gmail.com> wrote:
> > On Sat, Jun 18, 2011 at 1:32 AM, Jan Hubicka <hubicka@ucw.cz> wrote:
> >> Hi,
> >> this patch makes symetric changes to varpool as did the prevoius series to cgraph.
> >> Basically the aliases are now represented as separate varpool nodes with alias reference
> >> to the variable they refer to, with some infrastructure to walk the alias references
> >> as needed.
> >>
> >> Bootstrapped/regtested x86_64-linux, comitted.
> >>
> >> Honza
> >>
> >> ? ? ? ?* lto-symtab.c (lto_varpool_replace_node): Remove code handling
> >> ? ? ? ?extra name aliases.
> >> ? ? ? ?(lto_symtab_resolve_can_prevail_p): Likewise.
> >> ? ? ? ?(lto_symtab_merge_cgraph_nodes): Update alias_of pointers..
> >> ? ? ? ?* cgraphbuild.c (record_reference): Remove extra body alias code.
> >> ? ? ? ?(mark_load): Likewise.
> >> ? ? ? ?(mark_store): Likewise.
> >> ? ? ? ?* cgraph.h (varpool_node): Remove extra_name filed;
> >> ? ? ? ?add alias_of and extraname_alias.
> >> ? ? ? ?(varpool_create_variable_alias, varpool_for_node_and_aliases): Declare.
> >> ? ? ? ?(varpool_alias_aliased_node): New inline function.
> >> ? ? ? ?(varpool_variable_node): New function.
> >> ? ? ? ?* cgraphunit.c (handle_alias_pairs): Handle also variable aliases.
> >> ? ? ? ?* ipa-ref.c (ipa_record_reference): Allow aliases on variables.
> >> ? ? ? ?* lto-cgraph.c (lto_output_varpool_node): Update streaming.
> >> ? ? ? ?(input_varpool_node): Likewise.
> >> ? ? ? ?* lto-streamer-out.c (produce_symtab): Remove extra name aliases.
> >> ? ? ? ?(varpool_externally_visible_p): Remove extra body alias code.
> >> ? ? ? ?(function_and_variable_visibility): Likewise.
> >> ? ? ? ?* tree-ssa-structalias.c (associate_varinfo_to_alias_1): New function.
> >> ? ? ? ?(ipa_pta_execute): Use it.
> >> ? ? ? ?* varpool.c (varpool_remove_node): Remove extra name alias code.
> >> ? ? ? ?(varpool_mark_needed_node): Likewise.
> >> ? ? ? ?(varpool_analyze_pending_decls): Analyze aliases.
> >> ? ? ? ?(assemble_aliases): New functoin.
> >> ? ? ? ?(varpool_assemble_decl): Use it.
> >> ? ? ? ?(varpool_create_variable_alias): New function.
> >> ? ? ? ?(varpool_extra_name_alias): Rewrite.
> >> ? ? ? ?(varpool_for_node_and_aliases): New function.
> >
> > This caused:
> >
> > http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49463
> >
>
> This patch is incorrect as shown in the PR above.
The builtins/strstr-asm.c is the same issue as I patched some time ago in
http://gcc.gnu.org/ml/gcc-patches/2010-12/msg00031.html
just in this case the problem remained hidden until now.
Again the problem needs plugin to manifest.
There are two problems here
1) We do not stream builtin decls and merge them outside lto-symtab (by just
streaming references to builtins with their asm names). There is at least
one extra PR related to this and on my TODO is to simply remove the code.
2) Aliases within single unit works only when both the alias and the target use
asm name. This is because internally we store mangled DECL_ASSEMBLER_NAME and the
alias_pair code.
With LTO this breaks existing code simply because what used to be multiple units
and thus safe is now single LTO unit.
Dave Korn fixed part of the problem by introducing mangling code into lto-symtab
His code solve similar problems with aliases from the asm code, but it
did not solve the problem with aliases from LTO units, like here, simply
because alias pair code bypass the lto-symtab. One of goals of the incorrect patch
above is to make lto-symtab to do the merging and thus fix this issue (for now at
all decls except for builtins).
Still it would be good to solve the problem on non-LTO compilation, too.
We discussed introduction of proper symbol table into GCC at the GCC gathering last
weekend. It is where I am heading but it will take some time.
Until that happens, I suggest fixing the testcase same was as we already fixed
the memops-asm-lib.c in 4.6 timeframe.
Bootstrapped/regtested x86_64-linux, OK?
Index: strstr-asm-lib.c
===================================================================
--- strstr-asm-lib.c (revision 175183)
+++ strstr-asm-lib.c (working copy)
@@ -7,6 +7,7 @@
extern int inside_main;
extern const char *p;
+__attribute__ ((used))
char *
my_strstr (const char *s1, const char *s2)
{