Re: [PR48866] three alternative fixes

[Alexandre Oliva <aoliva at redhat dot com>]

On Apr  9, 2012, Alexandre Oliva <aoliva@redhat.com> wrote:

> On Jun  2, 2011, Alexandre Oliva <aoliva@redhat.com> wrote:
>> On May 30, 2011, Alexandre Oliva <aoliva@redhat.com> wrote:
>>> On May 30, 2011, Alexandre Oliva <aoliva@redhat.com> wrote:

>>>> I have 3 different, mutually exclusive patches that fix PR 48866.  The
>>>> problem is exponential time while dealing with an expression that
>>>> resulted from a long chain of replaceable insns with memory accesses
>>>> moved past the debug insns referring to their results.

>>>> 1. emit debug temps for replaceable DEFs that end up being referenced in
>>>> debug insns.  We already have some code to try to deal with this, but it
>>>> emits the huge expressions we'd rather avoid, and it may create
>>>> unnecessary duplication.  This new approach emits a placeholder instead
>>>> of skipping replaceable DEFs altogether, and then, if the DEF is
>>>> referenced in a debug insn (perhaps during the late debug re-expasion of
>>>> some other placeholder), it is expanded.  Placeholders that end up not
>>>> being referenced are then throw away.

>>> This is my favorite option, for it's safest: it doesn't change
>>> executable code at all (or should I say it *shouldn't* change it, for I
>>> haven't verified that it doesn't), retaining any register pressure
>>> benefits from TER.

>> This revised and retested version records expansions in an array indexed
>> on SSA version rather than a pointer_map, as suggested by Matz.

> Updated to deal with debug source bind stmts, added an assertion in
> var-tracking to make sure we don't get unexpected kinds of decls in
> VAR_LOCATION insns.  Regstrapped on x86_64-linux-gnu and i686-linux-gnu.
> Ok to install?

> for  gcc/ChangeLog
> from  Alexandre Oliva  <aoliva@redhat.com>

> 	PR debug/48866
> 	* cfgexpand.c (DEBUG_INSN_TOEXPAND): New.
> 	(def_expansions): New.
> 	(def_expansions_init): New.
> 	(def_expansions_remove_placeholder, def_expansions_fini): New.
> 	(def_get_expansion_ptr): New.
> 	(expand_debug_expr): Create debug temps as needed.
> 	(expand_debug_insn): New, split out of...
> 	(expand_debug_locations): ... this.
> 	(gen_emit_debug_insn): New, split out of...
> 	(expand_gimple_basic_block): ... this.  Simplify expansion of
> 	debug stmts.  Emit placeholders for replaceable DEFs, rather
> 	than debug temps at last non-debug uses.
> 	(gimple_expand_cfg): Initialize and finalize expansions cache.
> 	* var-tracking.c (use_type): Check for acceptable var decls in
> 	var_locations.

Ping?  http://gcc.gnu.org/ml/gcc-patches/2012-04/msg00413.html

-- 
Alexandre Oliva, freedom fighter    http://FSFLA.org/~lxoliva/
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