This is a general m68k code generation regression. Starting with revision
150588 GCC for m68k generates "surprising" code for auto increments, eg.
for a strlcpy implementation. Compiling this code with the 4.5.0 snapshot
from 20100107 yields:
-- 4.5.0 --
_strlcpy:
movel d3,s...@-
movel d2,s...@-
movel sp@(16),d0
movel sp@(20),d1
jeq L7
movel d0,a0
movel sp@(12),a1
L3:
movel a0,d2
subql #1,d1
jeq L11
moveb a...@+,d2
moveb d2,a...@+
movel a0,d3 | <--
tstb d2 | <--
jne L3
L4:
subl d3,d0
notl d0
movel s...@+,d2
movel s...@+,d3
rts
L7:
movel d0,d2
movel d2,a0
L6:
moveb a...@+,d1
movel a0,d3 | <--
tstb d1 | <--
jeq L4
moveb a...@+,d1
movel a0,d3 | <--
tstb d1 | <--
jne L6
jra L4
L11:
clrb a1@
movel d2,a0
jra L6
-- cut --
Suddenly GCC inserts "useless" moves and because of these moves has also
to generate explicit tst instructions. Older GCC versions generated better
code by using tst.b incrementing an address register without extra move
instructions, i.e. 4.4.0:
-- 4.4.0 (release) --
_strlcpy:
movel d2,s...@-
movel sp@(8),a1
movel sp@(12),d0
movel sp@(16),d1
jne L2
movel d0,a0
L8:
tstb a...@+
jne L8
L5:
subl a0,d0
notl d0
movel s...@+,d2
rts
L2:
movel d0,a0
subql #1,d1
jeq L11
L6:
moveb a...@+,d2
moveb d2,a1@
jeq L5
addql #1,a1
subql #1,d1
jne L6
L11:
clrb a1@
tstb a...@+
jne L8
jra L5
-- cut --
Environment:
System: FreeBSD 6.3-STABLE #0: Sat Mar 1 11:12:32 CET 2008
r...@sirius:/usr/obj/usr/src/sys/SIRIUS i386
host: i386-unknown-freebsd6.3
build: i386-unknown-freebsd6.3
target: m68k-unknown-amigaos
configured with: ../gcc-4.5-gg/configure --disable-nls --disable-libssp
--enable-languages=c --with-gmp=/usr/local --disable-tls --target=m68k-amigaos
How-To-Repeat:
Compiling the following code with
gcc-4.5.0 -O2 -fomit-frame-pointer strlcpy.c -o -
demonstrates the problem. FWIW, m68k-elf exhibits the very same problem!
-- cut --
typedef unsigned long size_t;
size_t
strlcpy(char *dst, const char *src, size_t n)
{ const char *s = src;
if (n) {
while (--n)
if ((*dst++ = *s++) == '\0')
goto out;
*dst = '\0';
}
while (*s++ != '\0')
continue;
out:
return ~(src - s);
}
-- cut --
------- Comment #1 from gnikl at users dot sourceforge dot net 2010-01-25
19:34 -------
Fix:
Reverting rev 150588 restores the previous behaviour.
--
Summary: [4.5] Regression whith auto increments
Product: gcc
Version: 4.5.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: middle-end
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: gnikl at users dot sourceforge dot net
GCC build triplet: i386-unknown-freebsd6.3
GCC host triplet: i386-unknown-freebsd6.3
GCC target triplet: m68k-unknown-amigaos
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=42863
