[cfe-dev] [llvm-dev] generate vectorized code

Rail Shafigulin via cfe-dev cfe-dev at lists.llvm.org
Fri Mar 18 14:17:02 PDT 2016


On Fri, Mar 18, 2016 at 2:03 PM, Rail Shafigulin <rail at esenciatech.com>
wrote:

> On Fri, Mar 18, 2016 at 1:53 PM, Mehdi Amini <mehdi.amini at apple.com>
> wrote:
>
>>
>> On Mar 18, 2016, at 1:47 PM, Rail Shafigulin <rail at esenciatech.com>
>> wrote:
>>
>> Yes this IR does not build or shuffle any vector. Try to write a function
>>> that takes 8 ints and a pointer to a <4xi32>, builds two vectors with the 8
>>> ints,
>>>
>>
>> This might sound like a dumb question, but how does one build a vector of
>> ints out of regular ints in IR?
>>
>>
>> See: http://llvm.org/docs/LangRef.html#vector-operations
>>
>> In short, the IR has "insertelement", which maps to "INSERT_VECTOR_ELT"
>> in SDAG and "extractelement", which maps to "EXTRACT_VECTOR_ELT" in SDAG.
>>
>> I usually find good example by grepping in the lit tests. Another way is
>> to write the function in clang, and run it with -O3 -emit-llvm -S to get a
>> good starting point.
>>
> I tried using clang test.c -O3 -emit-llvm -S, but the only I didn't see
> any of the insertvectorelt or extractvectorelt. I'm wondering how does one
> trigger vector operations?
>
> Below is the test.c file. It seemed to me like a good candidate for
> vectorization, however nothing happened. I would really appreciate  if you
> could point me in the right
> direction with respect to vector generation.
>
> Any help is appreciated.
>
>
>>
>> --
>> Mehdi
>>
>
>
>
> --
> Rail Shafigulin
> Software Engineer
> Esencia Technologies
>

Forgot to attach a C file. Here it is:

#define N 32

int main () {

  int  a[N], b[N];
  int c[N];

  for (int i = 0; i < N; ++i)
       c[i] = a[i] + b[i];

  int sum=0;
  for (int i = 0; i < N; ++i)
       sum += c[i];

  return sum;
}


-- 
Rail Shafigulin
Software Engineer
Esencia Technologies
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