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Date: Tue, 18 Jun 2002 08:56:00 -0000
From: fshvaige@cisco.com
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Subject: optimization/7067: -Os with -mcpu=powerpc optimizes for speed (?) instead of space
X-SW-Source: 2002-06/txt/msg00420.txt.bz2
List-Id: <gcc-prs.sourceware.org>


>Number:         7067
>Category:       optimization
>Synopsis:       -Os with -mcpu=powerpc optimizes for speed (?) instead of space
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    unassigned
>State:          open
>Class:          pessimizes-code
>Submitter-Id:   net
>Arrival-Date:   Tue Jun 18 08:06:13 PDT 2002
>Closed-Date:
>Last-Modified:
>Originator:     fshvaige@cisco.com
>Release:        3.1 20020510 (prerelease)
>Organization:
>Environment:
../gcc-3.1/configure --with-gcc-version-trigger=/home/install/gcc-3.1/gcc/version.c --host=i686-pc-linux-gnu --with-newlib --enable-target-optspace --target=ppc-eabi --prefix=/home/crossGCC/ppc-eabi --with-local-prefix=/home/crossGCC/ppc-eabi --program-prefix=ppc-eabi- --enable-languages=c,c++ -v --norecursion
>Description:
File test4.c:
unsigned f (unsigned v) {
  return v * 10;
}

Command line:
ppc-eabi-gcc -S -Os test4.c

Produced code (right, space optimized):
f:
  mulli 3,3,10
  blr

Command line:
ppc-eabi-gcc -S -Os -mcpu=powerpc test4.c

Produced code (wrong, probably speed optimized ?):
f:
  mr 0,3
  slwi 3,3,2
  add 3,3,0
  slwi 3,3,1
  blr

Note: instruction "mulli" present in powerpc and even used by the same compiler and same command line for the very alike function, so problem is somewhere in optimization.

File test4a.c:
unsigned f (unsigned v) {
  return v * 11;
}

Command line:
ppc-eabi-gcc -S -Os -mcpu=powerpc test4a.c

Produced code (right):
f:
  mulli 3,3,11
  blr
>How-To-Repeat:
ppc-eabi-gcc -S -Os test4.c
ppc-eabi-gcc -S -Os -mcpu=powerpc test4.c
ppc-eabi-gcc -S -Os -mcpu=powerpc test4a.c
>Fix:

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