llvm dev - Mar 2016 - vectorization for X86

I'm trying to vectorize a simple C code. My problem is that I don't
quite
understand the relationship between clang --target option and the cores
mentioned in X86.td as well as other X86 related options (such as -mtune).
Below are the command and the code that I'm trying to vectorize. The code
compiles but I don't see any vectors. What am I doing wrong? Any help is
appreciated.

clang -S x.c --target=x86_64-pc-gnu -mtune=core-avx2 -o x.x86.s -fvectorize
-fno-lax-vector-conversions -fslp-vectorize-aggressive -fslp-vectorize

#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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You need to enable an optimization level, this vectorizes for me:

clang -S x.c --target=x86_64-pc-gnu -mtune=core-avx2  -O3 -S -o -

-- 
Mehdi
> On Mar 16, 2016, at 2:29 PM, Rail Shafigulin via llvm-dev <llvm-dev at
lists.llvm.org> wrote:
> 
> I'm trying to vectorize a simple C code. My problem is that I don't
quite understand the relationship between clang --target option and the cores
mentioned in X86.td as well as other X86 related options (such as -mtune). Below
are the command and the code that I'm trying to vectorize. The code compiles
but I don't see any vectors. What am I doing wrong? Any help is appreciated.
> 
> clang -S x.c --target=x86_64-pc-gnu -mtune=core-avx2 -o x.x86.s -fvectorize
-fno-lax-vector-conversions -fslp-vectorize-aggressive -fslp-vectorize
> 
> #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
> _______________________________________________
> LLVM Developers mailing list
> llvm-dev at lists.llvm.org
> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev

On Wed, Mar 16, 2016 at 2:34 PM, Mehdi Amini <mehdi.amini at apple.com>
wrote:
> You need to enable an optimization level, this vectorizes for me:
>
> clang -S x.c --target=x86_64-pc-gnu -mtune=core-avx2  -O3 -S -o -
>
> --
> Mehdi

Thanks. It worked!

-- 
Rail Shafigulin
Software Engineer
Esencia Technologies
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Hi. I don't know how llvm works internally, but I guess the code you wrote
don't need any vectorization.
It's probably because its completely memory bound and hardware prefetch will
do the job for you.
You can force vectorization using some pragmas (I don't remember which). 
Regis
Altimesh

-----Message d'origine-----
De : "Rail Shafigulin via cfe-dev" <cfe-dev at lists.llvm.org>
Envoyé : ‎16/‎03/‎2016 23:00
À : "llvm-dev" <llvm-dev at lists.llvm.org>; "cfe-dev at
lists.llvm.org" <cfe-dev at lists.llvm.org>
Objet : [cfe-dev] vectorization for X86

I'm trying to vectorize a simple C code. My problem is that I don't
quite understand the relationship between clang --target option and the cores
mentioned in X86.td as well as other X86 related options (such as -mtune). Below
are the command and the code that I'm trying to vectorize. The code compiles
but I don't see any vectors. What am I doing wrong? Any help is appreciated.


clang -S x.c --target=x86_64-pc-gnu -mtune=core-avx2 -o x.x86.s -fvectorize
-fno-lax-vector-conversions -fslp-vectorize-aggressive -fslp-vectorize



#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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