Re: [patch] Fix PR tree-optimization/49771

[Ira Rosen <ira dot rosen at linaro dot org>]

On 25 July 2011 13:57, Richard Guenther <richard.guenther@gmail.com> wrote:
> 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.
>

I am sorry, it's my fault, resending the file.

Sorry,
Ira

> 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
>>>>
>>>
>>
>

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