[Bug c/25230] New: __sync_add_and_fetch cannot use condition flags from subl

["bcrl at kvack dot org" <gcc-bugzilla at gcc dot gnu dot org>]

The program below should generate code that looks something like:

fput:
 addl $-1,(%rdi)
 jne .L4
 jmp release
.L4:
 ret

But instead generates:

fput:
        movl    $-1, %eax
        lock
        xaddl   %eax, (%rdi)
        decl    %eax
        jne     .L4
        jmp     release
        .p2align 4,,7
.L4:
        rep ; ret

test program:
struct file {
        int counter;
};

void release(struct file *file);

void fput(struct file *file)
{
        if (__sync_add_and_fetch(&file->counter, -1) == 0)
                release(file);
}


-- 
           Summary: __sync_add_and_fetch cannot use condition flags from
                    subl
           Product: gcc
           Version: 4.2.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: bcrl at kvack dot org
 GCC build triplet: x86_64-unknown-linux
  GCC host triplet: x86_64-unknown-linux
GCC target triplet: x86_64-unknown-linux


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=25230