http://gcc.gnu.org/bugzilla/show_bug.cgi?id=54419
--- Comment #47 from Dominique d'Humieres <dominiq at lps dot ens.fr>
2012-09-06 16:01:09 UTC ---
The test in comment #20 is
/* end confdefs.h. */
int
main ()
{
void f(void){asm("rdrand %eax");}
;
return 0;
}
I have compiled it with clang 1.7 and gcc 4.4.6, 4.5.3, 4.6.3, 4.7.1, and 4.8.0
r191013 with
'-O0 -fdump-tree-all rdrand.c -save-temps'.
clang gives
In file included from rdrand.c:1:
rdrand.c:6:13: error: expected ';' at end of declaration
void f(void){asm("rdrand %eax");}
^
;
1 error generated.
gcc 4.4 and 4.5 gives
rdrand.c:6:no such instruction: `rdrand %eax'
and "grep rdrand rdrand.c.*"
rdrand.c.001t.tu:@2761 function_decl name: @2768 type: @2769 srcp:
rdrand.c:4
rdrand.c.001t.tu: srcp: rdrand.c:6 link:
static
rdrand.c.001t.tu:@2800 result_decl type: @3 scpe: @2761 srcp:
rdrand.c:4
rdrand.c.003t.original: __asm__ __volatile__("rdrand %eax"::);
rdrand.c.004t.gimple: __asm__ __volatile__("rdrand %eax");
rdrand.c.005t.nested: __asm__ __volatile__("rdrand %eax");
rdrand.c.008t.omplower: __asm__ __volatile__("rdrand %eax");
rdrand.c.009t.lower: __asm__ __volatile__("rdrand %eax");
rdrand.c.011t.eh: __asm__ __volatile__("rdrand %eax");
rdrand.c.012t.cfg: __asm__ __volatile__("rdrand %eax");
rdrand.c.013t.veclower: __asm__ __volatile__("rdrand %eax");
rdrand.c.021t.cleanup_cfg: __asm__ __volatile__("rdrand %eax");
rdrand.c.023t.ssa: __asm__ __volatile__("rdrand %eax");
rdrand.c.024t.einline2: __asm__ __volatile__("rdrand %eax");
rdrand.c.040t.release_ssa: __asm__ __volatile__("rdrand %eax");
rdrand.c.135t.cplxlower0: __asm__ __volatile__("rdrand %eax");
rdrand.c.140t.optimized: __asm__ __volatile__("rdrand %eax");
(with a bunch of additional hit in rdrand.c.001t.tu for 4.4).
For gcc 4.6 and above the test compiles without error and "grep rdrand
rdrand.c.*" gives
rdrand.c.001t.tu: srcp: rdrand.c:4 link:
extern
rdrand.c.001t.tu: srcp: rdrand.c:6 link:
static
rdrand.c.001t.tu:@2807 result_decl type: @3 scpe: @2768 srcp:
rdrand.c:4
rdrand.c.003t.original: __asm__ __volatile__("rdrand %eax"::);
rdrand.c.005t.nested: __asm__ __volatile__("rdrand %eax");
i.e., "f(void){asm("rdrand %eax");}" is discarded after rdrand.c.005t.nested.
If someone thinks it is a [4.6/4.7/4.8 Regression] or a new undocumented
feature, please read the end of comment #33!
I have tried to bootstrap 191018 with the patch in comment #20 and gcc 4.4
(which fails the test for rdrand) and it failed with "no such instruction:
`rdrand %eax'". I think this answer the concern expressed by Marc in comment
#29: the bootstrapping compiler is not used for the tests in
libstdc++-v3/configure (am I wrong to assume that they use the new built one?).
