[llvm-dev] Invoke loop vectorizer

[Xiaochu Liu via llvm-dev]

I'm not compiling it to x86. Should loop optimizer something independent of
the target? If so, should the vectorized code on IR level?

On Aug 12, 2016 11:39 AM, "Daniel Berlin" <dberlin at dberlin.org> wrote:

> cat > test.c
>
> #define SIZE 128
>
> 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;
>
> }
>
> [dannyb at dannyb-macbookpro3 11:37:20] ~ :) $ clang -O3  test.c -c
> -save-temps
> [dannyb at dannyb-macbookpro3 11:38:28] ~ :) $ pcregrep -i "^\s*p"
> test.s|less
>         pushq   %rbp
>         pshufd  $68, %xmm0, %xmm0       ## xmm0 = xmm0[0,1,0,1]
>         pslldq  $8, %xmm1               ## xmm1 =
> zero,zero,zero,zero,zero,zero,zero,zero,xmm1[0,1,2,3,4,5,6,7]
>         pshufd  $68, %xmm3, %xmm3       ## xmm3 = xmm3[0,1,0,1]
>         paddq   %xmm1, %xmm3
>         pshufd  $78, %xmm3, %xmm4       ## xmm4 = xmm3[2,3,0,1]
>         punpckldq       %xmm5, %xmm4    ## xmm4 =
> xmm4[0],xmm5[0],xmm4[1],xmm5[1]
>         pshufd  $212, %xmm4, %xmm4      ## xmm4 = xmm4[0,1,1,3]
>
>
>
> Note:
> It also vectorizes at SIZE=8.
>
> Not sure what the exact translation of options from clang-cl to clang is.
> Maybe try adding /O3?
>
>
>
>
> On Fri, Aug 12, 2016 at 11:23 AM, Xiaochu Liu <xiaochu1122 at gmail.com>
> wrote:
>
>> 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
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>>>>
>>>>
>>>
>
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