------- Comment #3 from m dot rosellini at f5 dot com 2009-07-09 20:29 -------
OK, maybe some assembly will make the issue clearer. Or perhaps you just want
to close this bug if you're not fixing bugs in the 4.1 compiler. I verified
that the problem does occur with 4.1 and that it does not occur with 4.2. The
relevant built-ins seem not to exist in 4.0.
Below is the output from a 4.1 compiler and a 4.2 compiler. I have annotated
the relevant instructions with "<<<". In the first example, from a 4.1
compiler, you can see that there is a constant of "0" passed to adcl (which is
incorrect), whereas in the second example, from a 4.2 compiler, there is a
constant of "-1" passed to adcl (which is correct).
seapddev(catalan) ~/ 503$ cat t.c
int
main(int ac, char **av)
{
volatile long long x;
__sync_fetch_and_add(&x, -1);
return x;
}
seapddev(catalan) ~/ 504$ gcc --version
gcc (GCC) 4.1.2 20080704 (Red Hat 4.1.2-44)
Copyright (C) 2006 Free Software Foundation, Inc.
This is free software; see the source for copying conditions. There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
seapddev(catalan) ~/ 505$ gcc -march=pentium t.c
seapddev(catalan) ~/ 506$ cat t.s
.file "t.c"
.text
.globl main
.type main, @function
main:
leal 4(%esp), %ecx
andl $-16, %esp
pushl -4(%ecx)
pushl %ebp
movl %esp, %ebp
pushl %edi
pushl %esi
pushl %ebx
pushl %ecx
subl $40, %esp
leal -24(%ebp), %eax
movl %eax, -36(%ebp)
movl -36(%ebp), %edx
movl (%edx), %eax
movl 4(%edx), %edx
movl %eax, -48(%ebp)
movl %edx, -44(%ebp)
.L2:
movl -48(%ebp), %eax
movl -44(%ebp), %edx
movl %eax, -56(%ebp)
movl %edx, -52(%ebp)
movl -56(%ebp), %ecx
movl -52(%ebp), %ebx
addl $-1, %ecx
adcl $0, %ebx <<<
movl %ecx, %esi
movl %ebx, %ecx
movl -36(%ebp), %edi
movl -56(%ebp), %eax
movl -52(%ebp), %edx
movl %esi, %ebx
lock
cmpxchg8b (%edi)
movl %eax, -48(%ebp)
movl %edx, -44(%ebp)
jne .L2
movl -24(%ebp), %eax
movl -20(%ebp), %edx
addl $40, %esp
popl %ecx
popl %ebx
popl %esi
popl %edi
popl %ebp
leal -4(%ecx), %esp
ret
.size main, .-main
.ident "GCC: (GNU) 4.1.2 20080704 (Red Hat 4.1.2-44)"
.section .note.GNU-stack,"",@progbits
seapddev(catalan) ~/ 507$
wayward ~/ 537$ cat t.c
int
main(int ac, char **av)
{
volatile long long x;
__sync_fetch_and_add(&x, -1);
return x;
}
wayward ~/ 538$ gcc-4.2 --version
i686-apple-darwin9-gcc-4.2.1 (GCC) 4.2.1 (Apple Inc. build 5574)
Copyright (C) 2007 Free Software Foundation, Inc.
This is free software; see the source for copying conditions. There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
wayward ~/ 539$ rm t.s
rm: t.s: No such file or directory
wayward ~/ 540$ gcc-4.2 -march=pentium -S t.c
wayward ~/ 541$ cat t.s
.text
.globl _main
_main:
pushl %ebp
movl %esp, %ebp
pushl %edi
pushl %esi
subl $64, %esp
leal -16(%ebp), %eax
movl %eax, -28(%ebp)
movl -28(%ebp), %edi
movl (%edi), %esi
movl 4(%edi), %edi
movl %esi, -40(%ebp)
movl %edi, -36(%ebp)
L2:
movl -40(%ebp), %eax
movl -36(%ebp), %edx
movl %eax, -64(%ebp)
movl %edx, -60(%ebp)
movl -64(%ebp), %esi
movl -60(%ebp), %edi
addl $-1, %esi
adcl $-1, %edi <<<
movl %esi, -44(%ebp)
movl %edi, %ecx
movl -28(%ebp), %esi
movl -64(%ebp), %eax
movl -60(%ebp), %edx
movl -44(%ebp), %edi
xchgl %ebx, %edi
lock
cmpxchg8b (%esi)
xchgl %ebx, %edi
movl %eax, -40(%ebp)
movl %edx, -36(%ebp)
jne L2
movl -16(%ebp), %eax
movl -12(%ebp), %edx
addl $64, %esp
popl %esi
popl %edi
popl %ebp
ret
.subsections_via_symbols
wayward ~/ 542$
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=40693
