This is reproduceable with gcc 4.0.0 and gcc SVN, but not with gcc 3.4.6.
I still don't really know what's the problem, but I think it may be that not
enough registers are available for output, and gcc is using the same register
for 2 different outputs.
gccs were built with:
--prefix=/usr --enable-languages=c --program-suffix=-{svn,4.0.0}
file was compiled with:
gcc-{svn,4.0.0} -v -save-temps -O3 -c regs.c
The corresponding inline asm that triggers the error is the following, when
used many times in a function inside many ifs:
asm volatile (
"cmpl %0, %3\n\t"
"cmovl %3, %0\n\t"
"cmovl %4, %1\n\t"
"cmovl %5, %2\n\t"
: "+r" (dmin), "+r" (dx), "+r" (dy)
: "r" (d), "r" (val1), "r" (val2)
);
The problem can be seen at the end of the assembly file:
# 47 "regs.c" 1
cmpl %edx, %esi
cmovl %esi, %edx
cmovl %edi, %eax
cmovl %ecx, %eax
# 0 "" 2
#NO_APP
movl %eax, %ebx
movl %eax, %edi
movl %eax, -36(%ebp)
movl %eax, -24(%ebp)
movl %edx, dmin
eax is used twice, both for dx and dy.
Test code minimized from motion_est.c from FFmpeg. Could be minimized further.
--
Summary: wrong registers used in cmov instruction
Product: gcc
Version: 4.3.0
Status: UNCONFIRMED
Severity: minor
Priority: P3
Component: inline-asm
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: ramiro at lisha dot ufsc dot br
GCC build triplet: i686-pc-linux-gnu
GCC host triplet: i686-pc-linux-gnu
GCC target triplet: i686-pc-linux-gnu
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=31386
