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

[hameeza ahmed via llvm-dev]

but now it works fine with mentioned code.

On Sun, Jul 2, 2017 at 1:28 PM, Hal Finkel <hfinkel at anl.gov> wrote:

>
> On 07/01/2017 05:33 PM, hameeza ahmed wrote:
>
> I am able to vectorize it with the following code;
>
> #include <stdio.h>
> #define N 100351
>
> // This function computes 2D-5 point Jacobi stencil
> void stencil(int a[][N], int b[][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];
>
> }
> }
>
> I removed restrict over here.
>
>
> That seems odd. Can you please file a bug report?
>
>  -Hal
>
>
>
> On Sun, Jul 2, 2017 at 3:11 AM, hameeza ahmed <hahmed2305 at gmail.com>
> wrote:
>
>> 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
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>
>>>>
>>
>
> --
> Hal Finkel
> Lead, Compiler Technology and Programming Languages
> Leadership Computing Facility
> Argonne National Laboratory
>
>
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