+++ 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 [EMAIL PROTECTED],[EMAIL PROTECTED]
16: 20d9 movel [EMAIL PROTECTED],[EMAIL PROTECTED]
18: 20d9 movel [EMAIL PROTECTED],[EMAIL PROTECTED]
1a: 20d9 movel [EMAIL PROTECTED],[EMAIL PROTECTED]
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
