On 2012-08-31 05:48, Andrew MacLeod wrote:
> On 08/30/2012 07:04 PM, Richard Henderson wrote:
>> Actually, we already have a memory barrier feature in rtl:
>>
>> ALIAS_SET_MEMORY_BARRIER
>>
>> but since we already set that in get_builtin_sync_mem, we'll need
>> to figure out why that's no longer working.
>>
>> As far as I can tell from reading alias.c, we should already be
>> indicating that such memories alias...
>>
>> What was the testcase again? I seem to have lost the top of the thread...
>>
>>
>
> #include <atomic>
> using namespace std;
>
> atomic_uint a_8;
> int32_t g_70;
> int32_t g_141;
>
> int main (int, char *[]) {
> a_8.load () & a_8.load ();
> g_141 = g_70 != 0;
> }
>
> or equivalently
>
> int a_8;
> int g_70;
> int g_141;
>
> int main ()
> {
> __atomic_load_n (&a_8, __ATOMIC_SEQ_CST) & __atomic_load_n (&a_8,
> __ATOMIC_SEQ_CST);
> g_141 = g_70 != 0;
> }
Fixed as follows. This seems to be the only entry point in alias.c that didn't
take ALIAS_SET_MEMORY_BARRIER into account. Getting the above into a test case
is tricky, and I havn't figured out how to match it.
Full testing still underway, but I expect it to pass.
r~
* alias.c (read_dependence): Account for ALIAS_SET_MEMORY_BARRIER.
diff --git a/gcc/alias.c b/gcc/alias.c
index e9d701f..5848e75 100644
--- a/gcc/alias.c
+++ b/gcc/alias.c
@@ -2132,7 +2132,12 @@ memrefs_conflict_p (int xsize, rtx x, int ysize, rtx y,
HOST_WIDE_INT c)
int
read_dependence (const_rtx mem, const_rtx x)
{
- return MEM_VOLATILE_P (x) && MEM_VOLATILE_P (mem);
+ if (MEM_VOLATILE_P (x) && MEM_VOLATILE_P (mem))
+ return true;
+ if (MEM_ALIAS_SET (x) == ALIAS_SET_MEMORY_BARRIER
+ || MEM_ALIAS_SET (mem) == ALIAS_SET_MEMORY_BARRIER)
+ return true;
+ return false;
}
/* Returns nonzero if something about the mode or address format MEM1
