[Bug rtl-optimization/24414] New: Old-style asms don't clobber memory

[rth at gcc dot gnu dot org]

#include <signal.h>
#include <unistd.h>

int test;

void handler (int sig)
{
  test = 1;
}

int main()
{
  signal (SIGALRM, handler);
  alarm (1);
  while (test == 0)
    asm("");
  return 0;
}

Results in an infinite loop with -O2.  The load of test in main should not
be hoisted out of the loop.  A more x86-specific example (but without relying
on unix syscalls might be

int test;
int main()
{
  int x = test;
  asm("movl $1,test");
  if (x + test != 1)
    __builtin_trap ();
  return 0;
}

It also wouldn't surprise me if the two tests have different culprits...


-- 
           Summary: Old-style asms don't clobber memory
           Product: gcc
           Version: 4.0.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: rtl-optimization
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: rth at gcc dot gnu dot org


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=24414