Hi all:
Under studio 12.1, the following code snippet produces unexpected results when
compiled with optimization in 64-bit mode (code seems to work fine in 32-bit
mode, or without optimization):
#include <stdio.h>
#define rdtsc() \
({ unsigned long long __cycles; __asm__ __volatile__( \
"rdtsc" \
: "=A" (__cycles) ); __cycles; })
void
foo(unsigned a, unsigned b, unsigned c, unsigned d)
{
unsigned long long tsc;
tsc = rdtsc();
printf("%d\n", a * b * c * d);
}
int
main(int argc, char **argv)
{
unsigned a, b, c, d;
a = b = c = d = 1;
foo(a, b, c, d);
}
psg-solaris-01$ cc -V -m64 -O -o foo foo.c
cc: Sun C 5.10 SunOS_i386 2009/06/03
acomp: Sun C 5.10 SunOS_i386 Patch 142363-01 2009/07/15
iropt: Sun Compiler Common 12.1 SunOS_i386 Patch 141858-03 2009/09/21
ir2hf: Sun Compiler Common 12.1 SunOS_i386 Patch 141858-03 2009/09/21
ube: Sun Compiler Common 12.1 SunOS_i386 Patch 141858-03 2009/09/21
as: Sun Compiler Common 12.1 SunOS_i386 Patch 141858-03 2009/09/21
ld: Software Generation Utilities - Solaris Link Editors: 5.11-1.1685
psg-solaris-01$ ./foo
964055
It appears that the compiler is not recognizing that %eax/%edx will be
clobbered in this case. If I explicitly add those registers to the asm clobber
list, things work fine:
#define rdtsc() \
({ unsigned long long __cycles; __asm__ __volatile__( \
"rdtsc" \
: "=A" (__cycles) : : "%eax","%edx" ); __cycles; })
psg-solaris-01$ cc -V -m32 -O -o foo foo.c
cc: Sun C 5.10 SunOS_i386 2009/06/03
acomp: Sun C 5.10 SunOS_i386 Patch 142363-01 2009/07/15
iropt: Sun Compiler Common 12.1 SunOS_i386 Patch 141858-03 2009/09/21
ir2hf: Sun Compiler Common 12.1 SunOS_i386 Patch 141858-03 2009/09/21
ube: Sun Compiler Common 12.1 SunOS_i386 Patch 141858-03 2009/09/21
as: Sun Compiler Common 12.1 SunOS_i386 Patch 141858-03 2009/09/21
ld: Software Generation Utilities - Solaris Link Editors: 5.11-1.1685
psg-solaris-01$ ./foo
1
Is this correct behavior, or is this a bug that should be reported? My
understanding of the A constraint is that it is an alias for %eax/%edx.
thanks
Mark
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