[Bug target/53040] New: nested functions may trash floating point registers

[Bug target/53040] New: nested functions may trash floating point registers

[amodra at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=53040

             Bug #: 53040
           Summary: nested functions may trash floating point registers
    Classification: Unclassified
           Product: gcc
           Version: 4.8.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: target
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: amodra@gmail.com


compile with -m32 -Os -fno-inline
void ws_f (void)
{
  char b[10];
  void ns_f (void)
  {
    char a[33];
    __asm __volatile ("#%0 %1" : "=m" (a), "=m" (b) : : "fr28", "fr31");
  }
  ns_f ();
}

results in

ns_f.2345:
        stwu 1,-96(1)
        mflr 0
        stfd 28,64(1)
        stw 0,100(1)
        stfd 31,88(1)
[snip]
        addi 11,1,96
        b _restfpr_28_x

_restfpr_28_x will restore fr29 and fr30 from uninitialised stack.

[Bug target/53040] nested functions may trash floating point registers

[amodra at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=53040

--- Comment #1 from Alan Modra <amodra at gmail dot com> 2012-04-19 15:24:30 UTC ---
Created attachment 27191
  --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=27191
obvious fix

[Bug target/53040] nested functions may trash floating point registers

[amodra at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=53040

Alan Modra <amodra at gmail dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |ASSIGNED
   Last reconfirmed|                            |2012-04-19
     Ever Confirmed|0                           |1

[Bug target/53040] nested functions may trash floating point registers

[amodra at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=53040

--- Comment #2 from Alan Modra <amodra at gcc dot gnu.org> 2012-04-20 09:33:23 UTC ---
Author: amodra
Date: Fri Apr 20 09:33:19 2012
New Revision: 186616

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=186616
Log:
    PR target/53040
    * config/rs6000/rs6000.c (rs6000_savres_strategy): When using
    static chain, set REST_INLINE_FPRS too.


Modified:
    trunk/gcc/ChangeLog
    trunk/gcc/config/rs6000/rs6000.c

[Bug target/53040] nested functions may trash floating point registers

[amodra at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=53040

Alan Modra <amodra at gmail dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|ASSIGNED                    |RESOLVED
         Resolution|                            |FIXED

--- Comment #3 from Alan Modra <amodra at gmail dot com> 2013-02-06 02:39:54 UTC ---
Fixed.  Not a regression so not applying to FSF branches.

[Bug target/53040] nested functions may trash floating point registers

[amodra at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=53040

--- Comment #4 from Alan Modra <amodra at gcc dot gnu.org> 2013-02-06 02:46:24 UTC ---
Author: amodra
Date: Wed Feb  6 02:46:13 2013
New Revision: 195778

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=195778
Log:
    PR target/53040
    * config/rs6000/rs6000.c (rs6000_savres_strategy): When using
    static chain, set REST_INLINE_FPRS too.


Modified:
    branches/ibm/gcc-4_7-branch/gcc/ChangeLog.ibm
    branches/ibm/gcc-4_7-branch/gcc/config/rs6000/rs6000.c

[Bug target/53040] nested functions may trash floating point registers

[ebotcazou at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=53040

Eric Botcazou <ebotcazou at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |ebotcazou at gcc dot
                   |                            |gnu.org

--- Comment #5 from Eric Botcazou <ebotcazou at gcc dot gnu.org> 2013-02-06 11:49:59 UTC ---
Can you reconsider?  If that's an obvious fix for an annoying target problem,
then it should be put at least on the 4.7 branch.  There are plenty of
precedents for other targets (x86, SPARC, ARM, etc).

[Bug target/53040] nested functions may trash floating point registers

[amodra at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=53040

--- Comment #6 from Alan Modra <amodra at gmail dot com> 2013-02-06 13:31:45 UTC ---
This one is hardly an annoying bug.  You need
a) nested functions,
b) using floating point,
c) with an unusual set of callee saved fprs,
d) and -Os.

I found the bug only because I wrote a fairly complete test for
prologue/epilogue code.

OTOH, the patch is quite obvious and completely safe..

[Bug target/53040] nested functions may trash floating point registers

[ebotcazou at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=53040

--- Comment #7 from Eric Botcazou <ebotcazou at gcc dot gnu.org> 2013-02-06 16:45:44 UTC ---
> This one is hardly an annoying bug.  You need
> a) nested functions,
> b) using floating point,
> c) with an unusual set of callee saved fprs,
> d) and -Os.

a) + b) + d) is pretty much standard e.g. for embedded Ada on PowerPC/VxWorks.

> OTOH, the patch is quite obvious and completely safe..

Then I think it's a good candidate for a backport onto the 4.7 branch.

[Bug target/53040] nested functions may trash floating point registers

[dje at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=53040

David Edelsohn <dje at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |dje at gcc dot gnu.org

--- Comment #8 from David Edelsohn <dje at gcc dot gnu.org> 2013-02-06 22:25:21 UTC ---
Go ahead and backport it to 4.7 branch.

[Bug target/53040] nested functions may trash floating point registers

[amodra at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=53040

--- Comment #9 from Alan Modra <amodra at gcc dot gnu.org> 2013-02-07 01:39:29 UTC ---
Author: amodra
Date: Thu Feb  7 01:39:21 2013
New Revision: 195834

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=195834
Log:
    PR target/53040
    * config/rs6000/rs6000.c (rs6000_savres_strategy): When using
    static chain, set REST_INLINE_FPRS too.


Modified:
    branches/gcc-4_7-branch/gcc/ChangeLog
    branches/gcc-4_7-branch/gcc/config/rs6000/rs6000.c