Re: optimization/7005: Sibling and tail recursive calls optimisation with -fomit-frame-pointer: strange code generated.

Re: optimization/7005: Sibling and tail recursive calls optimisation with -fomit-frame-pointer: strange code generated.

[rth]

Synopsis: Sibling and tail recursive calls optimisation with -fomit-frame-pointer: strange code generated.

State-Changed-From-To: open->closed
State-Changed-By: rth
State-Changed-When: Fri Jun 14 16:31:12 2002
State-Changed-Why:
    x86 silliness fixed for 3.2.
    ppc backend doesn't support sibcalls.

http://gcc.gnu.org/cgi-bin/gnatsweb.pl?cmd=view%20audit-trail&database=gcc&pr=7005

Re: optimization/7005: Sibling and tail recursive calls optimisation with -fomit-frame-pointer: strange code generated.

[Andrew Pinski]

The following reply was made to PR optimization/7005; it has been noted by GNATS.

From: Andrew Pinski <pinskia@physics.uc.edu>
To: fshvaige@cisco.com
Cc: gcc-gnats@gcc.gnu.org
Subject: Re: optimization/7005: Sibling and tail recursive calls optimisation with -fomit-frame-pointer: strange code generated.
Date: Wed, 12 Jun 2002 09:36:09 -0400 (EDT)

 This has been fixed in gcc version 3.2 20020607 (experimental) at least for the i686 version.
 I did not check the ppc-eabi version but I do not think that the PowerPC version can be changed because the abi specifies this.
 
 Thanks,
 Andrew Pinski
 
 
 > >Description:
 > File test2.c:
 > 
 > int f1 (void);
 > int f2 (void) {
 >   return f1 ();
 > }
 > 
 > i686 -Os (best code):
 > 
 > f2:
 >   jmp     f1
 > 
 > i686 -O2/-O3 (Ooops):
 > 
 > f2:
 >   subl  $12, %esp
 >   addl  $12, %esp
 >   jmp f1
 > 
 > PowerPC -Os/-O2/-O3 (Ooops):
 > 
 > f2:
 >   stwu 1,-8(1)
 >   mflr 0
 >   stw 0,12(1)
 >   bl f1 
 >   lwz 0,12(1)
 >   addi 1,1,8 
 >   mtlr 0
 >   blr   
 > >How-To-Repeat:
 > gcc -S -Os test2.c -Wall -fomit-frame-pointer
 > gcc -S -O2 test2.c -Wall -fomit-frame-pointer
 > gcc -S -O3 test2.c -Wall -fomit-frame-pointer
 > ppc-eabi-gcc -S -Os test2.c -Wall -fomit-frame-pointer
 > ppc-eabi-gcc -S -O2 test2.c -Wall -fomit-frame-pointer
 > ppc-eabi-gcc -S -O3 test2.c -Wall -fomit-frame-pointer
 

optimization/7005: Sibling and tail recursive calls optimisation with -fomit-frame-pointer: strange code generated.

[fshvaige]

>Number:         7005
>Category:       optimization
>Synopsis:       Sibling and tail recursive calls optimisation with -fomit-frame-pointer: strange code generated.
>Confidential:   no
>Severity:       non-critical
>Priority:       medium
>Responsible:    unassigned
>State:          open
>Class:          pessimizes-code
>Submitter-Id:   net
>Arrival-Date:   Wed Jun 12 06:16:04 PDT 2002
>Closed-Date:
>Last-Modified:
>Originator:     fshvaige@cisco.com
>Release:        3.1 and 3.1 20020510 (prerelease)
>Organization:
>Environment:

>Description:
File test2.c:

int f1 (void);
int f2 (void) {
  return f1 ();
}

i686 -Os (best code):

f2:
  jmp     f1

i686 -O2/-O3 (Ooops):

f2:
  subl  $12, %esp
  addl  $12, %esp
  jmp f1

PowerPC -Os/-O2/-O3 (Ooops):

f2:
  stwu 1,-8(1)
  mflr 0
  stw 0,12(1)
  bl f1 
  lwz 0,12(1)
  addi 1,1,8 
  mtlr 0
  blr   
>How-To-Repeat:
gcc -S -Os test2.c -Wall -fomit-frame-pointer
gcc -S -O2 test2.c -Wall -fomit-frame-pointer
gcc -S -O3 test2.c -Wall -fomit-frame-pointer
ppc-eabi-gcc -S -Os test2.c -Wall -fomit-frame-pointer
ppc-eabi-gcc -S -O2 test2.c -Wall -fomit-frame-pointer
ppc-eabi-gcc -S -O3 test2.c -Wall -fomit-frame-pointer
>Fix:

>Release-Note:
>Audit-Trail:
>Unformatted: