RFR: 8275317: AArch64: Support some type conversion vectorization in SLP

[Jatin Bhateja]

On Fri, 12 Nov 2021 06:30:42 GMT, Fei Gao <duke at openjdk.java.net> wrote:

>> Current SLP vectorizer in C2 compiler doesn't support type conversion
>> operations. But AArch64 has vector type conversion instructions in
>> both NEON and SVE.
>> 
>> The type conversion involves two kinds of scenarios, conversion between
>> the same data sizes and conversion between different data sizes. If we
>> want to support casts between different data sizes, we need to amend
>> the code part for identifying adjacent memory references and the code
>> part for justifying if the combination is profitable. I suppose it
>> would be easier to review if we split the whole task to support type
>> conversion into two separate patches, one for the same data sizes and
>> the other one for different data sizes. The goal of this patch is just
>> to support conversions within the same data size, including:
>>   int -> float
>>   float -> int
>>   long -> double
>>   double -> long
>> 
>> A typical test case:
>> 
>> for (int i = start; i < limit; i++) {
>>     b[i] = (float) a[i];
>> }
>> 
>> To implement it, the patch completed the necessary instructions and
>> matching rules in the backend and added implementation for SLP in
>> the middle end.
>> 
>> The percentage of performance uplift on aarch64 system:
>> Mode: avgt
>> Cnt: 15
>> Metric: (ns/op)
>> 
>> benchmark                       percentage change  [(After-Before)/Before] 
>> VectorLoop.convertD2L      -48.46%	                 
>> VectorLoop.convertF2I        -55.67%
>> VectorLoop.convertI2F        -55.27%
>> VectorLoop.convertL2D       -48.75%
>
>> A second review would be good.
>> 
>> /reviewers 2
> 
> Thanks for your review, @TobiHartmann . Can I get a second review please?

Hi @fg1417 , Thanks for fixing this, I have X86 backend changes for missing same sized vector cast operations. Will push for review after this PR gets integrated.

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PR: https://git.openjdk.java.net/jdk/pull/6145