[llvm-dev] Jacobi 5 Point Stencil Code not Vectorizing

[hameeza ahmed via llvm-dev]

further i modified the code to the following;

#include <stdio.h>
#define N 100351

// This function computes 2D-5 point Jacobi stencil
void stencil(int a[restrict][N], int b[restrict][N])
{
   int i, j, k;
   for (k = 0; k < N; k++) {
       for (i = 1; i <= N-2; i++)
           for (j = 1; j <= N-2; j++)
        b[i][j] = 0.25 * (a[i][j] + a[i-1][j] + a[i+1][j] + a[i][j-1] +
a[i][j+1]);

for (i = 1; i <= N-2; i++)
for (j = 1; j <= N-2; j++)
 a[i][j] = b[i][j];

}
}

   but still no vectorization in IR. Also, when I set vector width
explicitly to 64, it gives the following error:

remark: <unknown>:0:0: loop not vectorized: call instruction cannot be
vectorized
remark: <unknown>:0:0: loop not vectorized: value that could not be
identified as reduction is used outside the loop

I need serious help on this. Please guide me.

On Sun, Jul 2, 2017 at 1:54 AM, hameeza ahmed <hahmed2305 at gmail.com> wrote:

> Does it happen due to loop carried dependence? if yes what is the solution
> to vectorize such codes?
>
>
> please reply. i m waiting.
>
> On Jul 1, 2017 12:30 PM, "hameeza ahmed" <hahmed2305 at gmail.com> wrote:
>
>> I even tried polly but still my llvm IR does not contain vector
>> instructions. i used the following command;
>>
>> clang  -S -emit-llvm stencil.c -march=knl -O3 -mllvm -polly -mllvm
>> -polly-vectorizer=stripmine -o stencil_poly.ll
>>
>> Please specify what is wrong with my code?
>>
>>
>> On Sat, Jul 1, 2017 at 4:08 PM, hameeza ahmed <hahmed2305 at gmail.com>
>> wrote:
>>
>>> Hello,
>>>
>>> I am trying to vectorize following stencil code;
>>>
>>> #include <stdio.h>
>>> #define N 100351
>>>
>>> // This function computes 2D-5 point Jacobi stencil
>>> void stencil(int a[restrict][N])
>>> {
>>>    int i, j, k;
>>>    for (k = 0; k < 100; k++)
>>>      {  for (i = 1; i <= N-2; i++)
>>>          {  for (j = 1; j <= N-2; j++)
>>>         { a[i][j] = 0.25 * (a[i][j] + a[i-1][j] + a[i+1][j] + a[i][j-1]
>>> + a[i][j+1]);
>>>               }
>>> }
>>> }}
>>>
>>> I have used the following commands
>>>
>>> clang  -S -emit-llvm stencil.c -march=knl -O3 -mllvm
>>> -disable-llvm-optzns -o stencil.ll
>>>
>>> opt  -S -O3 stencil.ll -o stencil_o3.ll
>>>
>>> llc -x86-asm-syntax=intel stencil_o3.ll -o stencil.s
>>>
>>> But the code is not vectorized. It still uses the scalar instructions;
>>>
>>> Please correct me.
>>>
>>> Thank You
>>>
>>>
>>>
>>>
>>>
>>
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