On Mon, Apr 9, 2012 at 7:02 PM, Richard Guenther
<[email protected]> wrote:
> On Mon, Apr 9, 2012 at 8:00 AM, Bin.Cheng <[email protected]> wrote:
>> On Fri, Mar 30, 2012 at 5:43 PM, Bin.Cheng <[email protected]> wrote:
>>
>> Hi Richard,
>> I am testing a patch to sink load of memory to proper basic block.
>> Everything goes fine except auto-vectorization, sinking of load sometime
>> corrupts the canonical form of data references. I haven't touched auto-vec
>> before and cannot tell whether it's good or bad to do sink before auto-vec.
>> For example, the slp-cond-1.c
>>
>> <bb 3>:
>> # i_39 = PHI <i_32(11), 0(2)>
>> D.5150_5 = i_39 * 2;
>> D.5151_10 = D.5150_5 + 1;
>> D.5153_17 = a[D.5150_5];
>> D.5154_19 = b[D.5150_5];
>> if (D.5153_17 >= D.5154_19)
>> goto <bb 9>;
>> else
>> goto <bb 4>;
>>
>> <bb 9>:
>> d0_6 = d[D.5150_5]; <-----this is sunk from bb3
>> goto <bb 5>;
>>
>> <bb 4>:
>> e0_8 = e[D.5150_5]; <-----this is sunk from bb3
>>
>> <bb 5>:
>> # d0_2 = PHI <d0_6(9), e0_8(4)>
>> k[D.5150_5] = d0_2;
>> D.5159_26 = a[D.5151_10];
>> D.5160_29 = b[D.5151_10];
>> if (D.5159_26 >= D.5160_29)
>> goto <bb 10>;
>> else
>> goto <bb 6>;
>>
>>
>> <bb 10>:
>> d1_11 = d[D.5151_10]; <-----this is sunk from bb3
>> goto <bb 7>;
>>
>> <bb 6>:
>> e1_14 = e[D.5151_10]; <-----this is sunk from bb3
>>
>> <bb 7>:
>> .......
>>
>> I will look into auto-vect but not sure how to handle this case.
>>
>> Any comments? Thanks very much.
>
> Simple - the vectorizer expects empty latch blocks. So simply
> never sink stuff into latch-blocks - I think the current code already
> tries to avoid that for regular computations.
Seems not the story. The sinkto basic block is not latch basic block at all.
The problem is about if-conversion, code of the case in slp-cond-1.c is like:
__attribute__((noinline, noclone)) void
f4 (void)
{
int i;
for (i = 0; i < N/2; ++i)
{
int d0 = d[2*i], e0 = e[2*i];
int d1 = d[2*i+1], e1 = e[2*i+1];
k[2*i] = a[2*i] >= b[2*i] ? d0 : e0; <------example
k[2*i+1] = a[2*i+1] >= b[2*i+1] ? d1 : e1;
}
}
It is strictly formed in conditional operations, just like the output
of if-conversion pass before auto-vec.
Now sink pass sinks load of d0/e0 into then/else branch, since they
are partial dead code in the opposite branch, which corrupts the
canonical form.
Ideally, if-conversion pass should handle the sinked code and collapse
if-then-else into conditional operations.
But as showed by dump of if-conversion pass before auto-vect:
<bb 3>:
# i_39 = PHI <i_32(10), 0(2)>
# ivtmp.137_41 = PHI <ivtmp.137_38(10), 16(2)>
D.5150_5 = i_39 * 2;
D.5151_10 = D.5150_5 + 1;
D.5153_17 = a[D.5150_5];
D.5154_19 = b[D.5150_5];
if (D.5153_17 >= D.5154_19)
goto <bb 4>;
else
goto <bb 5>;
<bb 4>:
d0_6 = d[D.5150_5];
goto <bb 6>;
<bb 5>:
e0_8 = e[D.5150_5];
<bb 6>:
# d0_2 = PHI <d0_6(4), e0_8(5)>
k[D.5150_5] = d0_2;
It does not work as expected.
So I think sink pass is fine for this case, it is the if-conversion
pass need further investigation.
Comments? Thanks.
--
Best Regards.
