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Date: Wed, 30 Dec 2009 12:57:00 -0000
Subject: [Bug target/42553]  New: wrong code with -O1
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current trunk/branches on x86_64-linux-gnu. return values with different
compilers and different optimizations:

         -O0  -O1  -O2  -O3
gcc-4.1   0    2    2    2
gcc-4.3   0    2    2    2
gcc-4.4   2    0    0    0
gcc-4.5   0    1    0    0

  Matthias

#include <stdbool.h>
#include <stdio.h>

static bool atomic_test_and_reset_bit(unsigned long *v,unsigned long bit) {
  bool res;

  __asm__ __volatile__( "btr %2,%1\n"
                        "adc $0,%0\n"
                        :"=r"(res), "=m"(*v)
                        :"r"(bit), "r"(0)) ;
  return res ? 1 : 0;
}

int main(void)
{
  unsigned long flags = 0;
  int j;

  j = atomic_test_and_reset_bit(&flags, 2);

  printf("%d\n", j);

  return 0;
}


-- 
           Summary: wrong code with -O1
           Product: gcc
           Version: 4.4.3
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: target
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: debian-gcc at lists dot debian dot org
GCC target triplet: x86_64-linux-gnu


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=42553