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* [Bug c/36134]  New: GCC creates suboptimal ASM : usage of ADDA.L where LEA could be used
@ 2008-05-05 13:51 gunnar at greyhound-data dot com
  2008-05-07 19:34 ` [Bug target/36134] " rguenth at gcc dot gnu dot org
                   ` (7 more replies)
  0 siblings, 8 replies; 9+ messages in thread
From: gunnar at greyhound-data dot com @ 2008-05-05 13:51 UTC (permalink / raw)
  To: gcc-bugs

+++ This bug was initially created as a clone of Bug #36133 +++

Hello,

The ASM code created by GCC 4.2.1 for 68k/Coldfire platform is not optimal.
Comparing ASM output created by GCC 2.9 with GCC 4.2,
the generated code got partially much worse with GCC 4.


One problem that was visible a lot was that GCC used ADDA.L instead using the
shorter LEA instruction.

Please see the below example for details.
In line 28 and 2E you can see that two times the ADDA.L instructions was used,
where instead the shorter LEA instruction could have been used.



Example: C-source
Code:
void * copy_32x4a(void *destparam, const void *srcparam, size_t size)
{
        int *dest = destparam;
        const int *src = srcparam;
        int size32;
        size32 = size / 16;
        for (; size32; size32--) {
                *dest++ = *src++;
                *dest++ = *src++;
                *dest++ = *src++;
                *dest++ = *src++;
        }
}

Compile option: m68k-linux-gnu-gcc -mcpu=54455 -msoft-float -o example -Os
-fomit-frame-pointer example.c

Code generated by GCC 4.2:
04:       202f 000c       movel %sp@(12),%d0
08:       226f 0004       moveal %sp@(4),%a1
0c:       206f 0008       moveal %sp@(8),%a0
10:       e888            lsrl #4,%d0
12:       6022            bras 36
14:       2290            movel %a0@,%a1@
16:       2368 0004 0004  movel %a0@(4),%a1@(4)
1c:       2368 0008 0008  movel %a0@(8),%a1@(8)
22:       2368 000c 000c  movel %a0@(12),%a1@(12)
28:       d3fc 0000 0010  addal #16,%a1
2e:       d1fc 0000 0010  addal #16,%a0
34:       5380            subql #1,%d0
36:       4a80            tstl %d0
38:       66da            bnes 14
3a:       4e75            rts    

For comparison here is code that you would expect:
04:       202f 000c       movel %sp@(12),%d0
08:       226f 0004       moveal %sp@(4),%a1
0c:       206f 0008       moveal %sp@(8),%a0
10:       e888            lsrl #4,%d0
12:       6022            beq 20
14:       20d9            movel %a1@+,%a0@+
16:       20d9            movel %a1@+,%a0@+
18:       20d9            movel %a1@+,%a0@+
1a:       20d9            movel %a1@+,%a0@+
1c:       5380            subql #1,%d0
1e:       66da            bnes 14
20:       4e75            rts 

Compiler used:
m68k-linux-gnu-gcc -v
Using built-in specs.
Target: m68k-linux-gnu
Configured with: /scratch/shinwell/cf-fall-linux-lite/src/gcc-4.2/configure
--build=i686-pc-linux-gnu --host=i686-pc-linux-gnu --target=m68k-linux-gnu
--enable-threads --disable-libmudflap --disable-libssp --disable-libgomp
--disable-libstdcxx-pch --with-arch=cf --with-gnu-as --with-gnu-ld
--enable-languages=c,c++ --enable-shared --enable-symvers=gnu
--enable-__cxa_atexit --with-pkgversion=Sourcery G++ Lite 4.2-47
--with-bugurl=https://support.codesourcery.com/GNUToolchain/ --disable-nls
--prefix=/opt/freescale/usr/local/gcc-4.2.47-eglibc-2.5.47/m68k-linux
--with-sysroot=/opt/freescale/usr/local/gcc-4.2.47-eglibc-2.5.47/m68k-linux/m68k-linux-gnu/libc
--with-build-sysroot=/scratch/shinwell/cf-fall-linux-lite/install/m68k-linux-gnu/libc
--enable-poison-system-directories
--with-build-time-tools=/scratch/shinwell/cf-fall-linux-lite/install/m68k-linux-gnu/bin
--with-build-time-tools=/scratch/shinwell/cf-fall-linux-lite/install/m68k-linux-gnu/bin
Thread model: posix
gcc version 4.2.1 (Sourcery G++ Lite 4.2-47)


I hope that this report help you to improve the quality of GCC.

Kind regards

Gunnar von Boehn
--
P.S. I put the noticed issues in indivitual tivkets for easier tracking. I hope
that this is helpfull.


-- 
           Summary: GCC creates suboptimal ASM : usage of ADDA.L where LEA
                    could be used
           Product: gcc
           Version: 4.2.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: gunnar at greyhound-data dot com
 GCC build triplet: i686-pc-linux-gnu
  GCC host triplet: i686-pc-linux-gnu
GCC target triplet: m68k-linux-gnu


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=36134


^ permalink raw reply	[flat|nested] 9+ messages in thread
end of thread, other threads:[~2008-11-14 10:55 UTC | newest]

Thread overview: 9+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2008-05-05 13:51 [Bug c/36134] New: GCC creates suboptimal ASM : usage of ADDA.L where LEA could be used gunnar at greyhound-data dot com
2008-05-07 19:34 ` [Bug target/36134] " rguenth at gcc dot gnu dot org
2008-05-28 16:20 ` gunnar at greyhound-data dot com
2008-05-29 12:51 ` gunnar at greyhound-data dot com
2008-06-02 22:37 ` schwab at suse dot de
2008-06-10 15:24 ` gunnar at greyhound-data dot com
2008-06-12 14:27 ` gunnar at greyhound-data dot com
2008-11-14 10:51 ` ams at gcc dot gnu dot org
2008-11-14 10:55 ` ams at gcc dot gnu dot org

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