[Bug tree-optimization/59479] New: Inlining of static function bloats code size when Os

[Bug tree-optimization/59479] New: Inlining of static function bloats code size when Os

[amker.cheng at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=59479

            Bug ID: 59479
           Summary: Inlining of static function bloats code size when Os
           Product: gcc
           Version: 4.9.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: amker.cheng at gmail dot com

Created attachment 31424
  --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=31424&action=edit
The preprocessed file for newlib/libc/stdio/findfp.c

Hi, for attached preprocessed code from newlib/libc/stdio/findfp.c, GCC inlines
static function `std' even when optimizing for Os.
With command line:
$ ./arm-none-eabi-gcc -Os -mthumb -mcpu=cortex-m0 -c -xc findfp.E -o findfp.o

The dumped symbols are like:
    21: 00000009    16 FUNC    GLOBAL DEFAULT    1 _cleanup_r
    ...
    29: 00000055   224 FUNC    GLOBAL DEFAULT    1 __sinit
    ...
    41: 000001d5    24 FUNC    GLOBAL DEFAULT    1 __fp_unlock_all

With command line:
$ ./arm-none-eabi-gcc -Os -mthumb -mcpu=cortex-m0 -c -xc findfp.E -o findfp.o
-fno-inline

The dumped symbols are like:
     9: 00000018     0 NOTYPE  LOCAL  DEFAULT    1 $t
    10: 00000019    72 FUNC    LOCAL  DEFAULT    1 std.isra.0
    ...
    24: 00000009    16 FUNC    GLOBAL DEFAULT    1 _cleanup_r
    ...
    36: 0000009d    80 FUNC    GLOBAL DEFAULT    1 __sinit

This occurs on trunk and 4_8 branch.

[Bug tree-optimization/59479] Inlining of static function bloats code size when Os

[rguenth at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=59479

Richard Biener <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |WAITING
   Last reconfirmed|                            |2013-12-13
     Ever confirmed|0                           |1

--- Comment #1 from Richard Biener <rguenth at gcc dot gnu.org> ---
I think you likely see a 2nd-order effect.  Inlining a once called function
should not increase code size.  But of course optimization opportunities
exposed by it may trigger optimizers that are not well tuned to honor -Os.

So, can you narrow down the issue a bit?

[Bug tree-optimization/59479] Inlining of static function bloats code size when Os

[amker.cheng at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=59479

--- Comment #2 from bin.cheng <amker.cheng at gmail dot com> ---
I will investigate it later.  Just clarifying, the function is called three
times by the caller, it would increase code size usually.

BTW, could you explain a little about "2nd-order effect"?  I am not familiar
with the concept.  Thanks in advance.

[Bug ipa/59479] Inlining of static function bloats code size when Os

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=59479

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |marxin at gcc dot gnu.org
          Component|tree-optimization           |ipa

--- Comment #3 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Is there a misunderstanding of what called once means?  Does it mean only
called from one other function rather than one time?

I see std is called three times from __sinit rather than once in that function.