[llvm-dev] Invoke loop vectorizer

[Xiaochu Liu via llvm-dev]

Hi Daniel,

I increased the size of your test to be 128 but -stats still shows no loop
optimized...

Xiaochu

On Aug 12, 2016 11:11 AM, "Daniel Berlin" <dberlin at dberlin.org> wrote:

> It's not possible to know that A and B don't alias in this example.  It's
> almost certainly not profitable to add a runtime check given the size of
> the loop.
>
>
> try
>
> #define SIZE 8
>
> void bar(int *restrict A, int* restrict B,int K) {
>
>   #pragma clang loop vectorize(enable) vectorize_width(2) unroll_count(8)
>
>   for (int i = 0; i < SIZE; ++i)
>
>     A[i] += B[i] + K;
>
> }
>
> (i don't remember if llvm also does runtime alias checks, but if it does,
> you'd probably need to increase size to get it to vectorize)
>
> On Fri, Aug 12, 2016 at 11:08 AM, Xiaochu Liu via llvm-dev <
> llvm-dev at lists.llvm.org> wrote:
>
>> Hi Andrey,
>>
>> Thanks. I found even when loop vectorizer and SLP vectorizer are enabled,
>> my simple test still not get optimized. I also tried clang pragma in my
>> test to force vectorization. What do you think is the problem?
>>
>> Test:
>>
>> #define SIZE 8
>>
>> void bar(int *A, int* B,int K) {
>>
>>   #pragma clang loop vectorize(enable) vectorize_width(2) unroll_count(8)
>>
>>   for (int i = 0; i < SIZE; ++i)
>>
>>     A[i] += B[i] + K;
>>
>> }
>>
>> Thanks,
>> Xiaochu
>>
>> On Aug 12, 2016 4:06 AM, "Andrey Bokhanko" <andreybokhanko at gmail.com>
>> wrote:
>>
>>> Hi Xiaochu,
>>>
>>> Clang uses -O0 by default, that doesn't run any optimizations. Try
>>> supplying -O1 or higher.
>>>
>>> Yours,
>>> Andrey
>>>
>>>
>>> On Fri, Aug 12, 2016 at 1:04 AM, Xiaochu Liu via llvm-dev <
>>> llvm-dev at lists.llvm.org> wrote:
>>>
>>>> Hi there ,
>>>>
>>>> I use clang-cl /Qvec test.c to compile the code. But the pass
>>>> LoopVectorizer is never invoked.
>>>>
>>>> I was wondering if this is sufficient to enable auto vectorizer?
>>>>
>>>> Thanks,
>>>> Xiaochu
>>>>
>>>> _______________________________________________
>>>> LLVM Developers mailing list
>>>> llvm-dev at lists.llvm.org
>>>> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>>>>
>>>>
>>>
>> _______________________________________________
>> LLVM Developers mailing list
>> llvm-dev at lists.llvm.org
>> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>>
>>
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.llvm.org/pipermail/llvm-dev/attachments/20160812/d555cb15/attachment.html>