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

[hameeza ahmed via llvm-dev]

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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