[cfe-dev] [llvm-dev] vectorization for X86

Mehdi Amini via cfe-dev cfe-dev at lists.llvm.org
Wed Mar 16 14:34:45 PDT 2016


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
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