[llvm-dev] m32 flag disables vectorization

[Michael Zolotukhin via llvm-dev]

Hi,

I’d recommend using pass-remarks (add -pass-remarks=loop-vectorize to your opt invocation) - it might give some hints.

Michael

PS: For me it’s vectorized independently on using -m32:

> bin/clang -emit-llvm       -c -O0 1.c -o -  | bin/opt -mem2reg -loops -loop-simplify -loop-rotate -loop-vectorize -o /dev/null -pass-remarks=loop-vectorize
remark: <unknown>:0:0: vectorized loop (vectorization width: 4, interleaved count: 2)
remark: <unknown>:0:0: vectorized loop (vectorization width: 4, interleaved count: 2)

> bin/clang -emit-llvm -m32  -c -O0 1.c -o -  | bin/opt -mem2reg -loops -loop-simplify -loop-rotate -loop-vectorize -o /dev/null -pass-remarks=loop-vectorize
remark: <unknown>:0:0: vectorized loop (vectorization width: 4, interleaved count: 2)
remark: <unknown>:0:0: vectorized loop (vectorization width: 4, interleaved count: 2)

> bin/clang -v
clang version 4.0.0 (trunk 278549) (llvm/trunk 278569)
Target: x86_64-apple-darwin15.6.0
Thread model: posix

> On Jul 7, 2017, at 9:16 AM, Anastasiya Ruzhanskaya via llvm-dev <llvm-dev at lists.llvm.org> wrote:
> 
> Hello,
> 
> I have a simple loop,
> #include <stdio.h>
> #define N 200
> 
> int array[N];
> 
> int main() {
>     int result = 0;
>     int a, b, c;
>     for (b = 0; b < N; b++)
>         array[b] = b%3;
> 
> #pragma clang loop vectorize(enable)
>     for (a = 0; a < N; a++) {
>         result += array[a];
>     }
> 
>     return result;
> }
> 
> 
> I compile it like this:
> clang -emit-llvm -m32 -c -O0 myarray2.c -o myarray2.s
> opt -mem2reg -loops -loop-simplify -loop-rotate -loop-vectorize -S myarray2.s -o opt.s
> 
> and I don't see any effect of vectorization. When I delete m32 flag, vectorization is applied, Why does this happen?
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