[Bug target/39148] -Os increase code size when stack is aligned

[hjl dot tools at gmail dot com]

--- Comment #7 from hjl dot tools at gmail dot com  2009-02-12 02:37 ---
(In reply to comment #6)
> So simply enable ACCUMULATE_OUTGOING_ARGS for stack realign isn't be the best
> option for all cases either.
> 

OK. I am closing as WONTFIX.


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hjl dot tools at gmail dot com changed:

   What|Removed |Added

 Status|UNCONFIRMED |RESOLVED
 Resolution||WONTFIX


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=39148

[Bug target/39148] -Os increase code size when stack is aligned

[Joey dot ye at intel dot com]

--- Comment #6 from Joey dot ye at intel dot com  2009-02-12 02:33 ---
(In reply to comment #5)
> If ACCUMULATE_OUTGOING_ARGS is off, ECX will be used
> for stack alignment and it may lead to code size
> increase due to register spill since ia32 has very
> few registers.
The code increase resulted from stack realign are mainly from prologue
increase. ECX is only used as hard register in prologue/epilogue and the impact
to function body is low.

If ACCUMULATE_OUTGOING_ARGS does increase code size, then for big functions,
benefit of !ACCUMULATE_OUTGOING_ARGS will offset increase of prologue/epilogue.

So simply enable ACCUMULATE_OUTGOING_ARGS for stack realign isn't be the best
option for all cases either.


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=39148

[Bug target/39148] -Os increase code size when stack is aligned

[hjl dot tools at gmail dot com]

--- Comment #5 from hjl dot tools at gmail dot com  2009-02-12 00:44 ---
I tried -maccumulate-outgoing-args on 2.6 kernel:

   textdata bss dec hex filename
5136786  600084 1003520 6740390  66d9a6 vmlinux
5086759  600084 1003520 6690363  66163b /tmp/vmlinux.old

It does increase binary size. Should we consider to
turn on ACCUMULATE_OUTGOING_ARGS when stack is aligned?
If ACCUMULATE_OUTGOING_ARGS is off, ECX will be used
for stack alignment and it may lead to code size
increase due to register spill since ia32 has very
few registers.


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=39148

[Bug target/39148] -Os increase code size when stack is aligned

[hjl dot tools at gmail dot com]

--- Comment #4 from hjl dot tools at gmail dot com  2009-02-11 17:16 ---
(In reply to comment #3)
> If you mean setting ACCUMULATE_OUTGOING_ARGS to true, I bet that could help

Oops. Yes, I meant setting ACCUMULATE_OUTGOING_ARGS to true when stack
alignment is needed.

> very small functions that need dynamic realignment, but certainly for larger
> functions !ACCUMULATE_OUTGOING_ARGS results in smaller code, even if
> realignment is done.
> 

Joey and Xuepeng are running

http://www.inf.u-szeged.hu/csibe/

to see how ACCUMULATE_OUTGOING_ARGS affects code size.


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=39148

[Bug target/39148] -Os increase code size when stack is aligned

[jakub at gcc dot gnu dot org]

--- Comment #3 from jakub at gcc dot gnu dot org  2009-02-11 17:11 ---
If you mean setting ACCUMULATE_OUTGOING_ARGS to true, I bet that could help
very small functions that need dynamic realignment, but certainly for larger
functions !ACCUMULATE_OUTGOING_ARGS results in smaller code, even if
realignment is done.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=39148

[Bug target/39148] -Os increase code size when stack is aligned

[hjl dot tools at gmail dot com]

--- Comment #2 from hjl dot tools at gmail dot com  2009-02-11 15:54 ---
One way to fix this is to set ACCUMULATE_OUTGOING_ARGS to false
when we need stack alignment.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=39148

[Bug target/39148] -Os increase code size when stack is aligned

[hjl dot tools at gmail dot com]

--- Comment #1 from hjl dot tools at gmail dot com  2009-02-10 20:46 ---
The problem is

static rtx
ix86_get_drap_rtx (void)
{
  if (ix86_force_drap || !ACCUMULATE_OUTGOING_ARGS)
crtl->need_drap = true; 


-Os turns off ACCUMULATE_OUTGOING_ARGS, which turns on DRAP. Does
ACCUMULATE_OUTGOING_ARGS really increase code size?


-- 

hjl dot tools at gmail dot com changed:

   What|Removed |Added

 CC||jh at suse dot cz, ubizjak
   ||at gmail dot com


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=39148

[Bug target/39148] -Os increase code size when stack is aligned

[hjl dot tools at gmail dot com]

-- 

hjl dot tools at gmail dot com changed:

   What|Removed |Added

   Target Milestone|--- |4.4.0


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=39148