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Re: [patch] Fix PR tree-optimization/49771
On Mon, Jul 25, 2011 at 12:52 PM, Ira Rosen <ira.rosen@linaro.org> wrote:
> On 25 July 2011 12:39, Richard Guenther <richard.guenther@gmail.com> wrote:
>> On Mon, Jul 25, 2011 at 11:10 AM, Ulrich Weigand <uweigand@de.ibm.com> wrote:
>>> Richard Guenther wrote:
>>>> On Sun, Jul 24, 2011 at 2:02 PM, Ira Rosen <ira.rosen@linaro.org> wrote:
>>>> > On 21 July 2011 15:19, Ira Rosen <ira.rosen@linaro.org> wrote:
>>>> >> I reproduced the failure. It occurs without Richard's
>>>> >> (http://gcc.gnu.org/ml/gcc-patches/2011-07/msg01022.html) and this
>>>> >> patches too. Obviously the vectorized loop is executed, but at the
>>>> >> moment I don't understand why. I'll have a better look on Sunday.
>>>> >
>>>> > Actually it doesn't choose the vectorized code. But the scalar version
>>>> > gets optimized in a harmful way for SPU, AFAIU.
>>>> > Here is the scalar loop after vrp2
>>>> >
>>>> > <bb 8>:
>>>> > ?# ivtmp.42_50 = PHI <ivtmp.42_59(3), ivtmp.42_45(10)>
>>>> > ?D.4593_42 = (void *) ivtmp.53_32;
>>>> > ?D.4520_33 = MEM[base: D.4593_42, offset: 0B];
>>>> > ?D.4521_34 = D.4520_33 + 1;
>>>> > ?MEM[symbol: a, index: ivtmp.42_50, offset: 0B] = D.4521_34;
>>>> > ?ivtmp.42_45 = ivtmp.42_50 + 4;
>>>> > ?if (ivtmp.42_45 != 16)
>>>> > ? ?goto <bb 10>;
>>>> > ?else
>>>> > ? ?goto <bb 5>;
>>>> >
>>>> > and the load is changed by dom2 to:
>>>> >
>>>> > <bb 4>:
>>>> > ?...
>>>> > ?D.4520_33 = MEM[base: vect_pa.9_19, offset: 0B];
>>>> > ? ...
>>>> >
>>>> > where vector(4) int * vect_pa.9;
>>>> >
>>>> > And the scalar loop has no rotate for that load:
>>>>
>>>> Hum. ?This smells like we are hiding sth from the tree optimizers?
>>>
>>> Well, the back-end assumes a pointer to vector type is always
>>> naturally aligned, and therefore the data it points to can be
>>> accessed via a simple load, with no extra rotate needed.
>>
>> I can't see any use of VECTOR_TYPE in config/spu/, and assuming
>> anything about alignment just because of the kind of the pointer
>> is bogus - the scalar code does a scalar read using that pointer.
>> So the backend better should look at the memory operation, not
>> at the pointer type. ?That said, I can't find any code that looks
>> suspicious in the spu backend.
>>
>>> It seems what happened here is that somehow, a pointer to int
>>> gets replaced by a pointer to vector, even though their alignment
>>> properties are different.
>>
>> No, they are not. ?They get replaced if they are value-equivalent
>> in which case they are also alignment-equivalent. ?But well, the
>> dump snippet wasn't complete and I don't feel like building a
>> SPU cross to verify myself.
>
> I am attaching the complete file.
The issue seems to be that the IV in question, vect_pa.9_19, is
defined as
vect_pa.9_19 = (vector(4) int *) ivtmp.53_32;
but ivtmp.53_32 does not have a definition at all.
Richard.
>
> Thanks,
> Ira
>
>
>
>>
>>> This vector pointer must originate somehow in the vectorizer,
>>> however, since the original C source does not contain any
>>> vector types at all ...
>>
>> That's for sure true, it must be the initial pointer we then increment
>> in the vectorized loop.
>>
>> Richard.
>>
>>> Bye,
>>> Ulrich
>>>
>>> --
>>> ?Dr. Ulrich Weigand
>>> ?GNU Toolchain for Linux on System z and Cell BE
>>> ?Ulrich.Weigand@de.ibm.com
>>>
>>
>