RFR: 8257483: C2: Split immediate vector rotate from RotateLeftV and RotateRightV nodes [v5]

[Vladimir Ivanov]

On Wed, 9 Dec 2020 06:29:50 GMT, Dong Bo <dongbo at openjdk.org> wrote:

>> Currently, for all CPUs, if optimizing RotateLeftV and RotateRightV with match rules in AD files, we have to implement both immediate and variable versions.
>> 
>> On aarch64, with match rules for vector rotation, immediate vector rotatation can be optimized with shift+insert instructions (i.e. SLI/SRI, ~20% improvements with an initial implementation).
>> However there woule be performance regression for variable version, due to SLI/SRI have no register version in NEON intruction set and there is no register version for right shift neither.
>> The instructions for match rules of vector rotate variable should be:
>>     mov w9, 32
>>     dup v13.4s, w9
>>     sub  v20.4s, v13.4S, v19.4s
>>     # For a loop, default version only has code below,
>>     # the code above (loop invariants) are put outside of a loop.
>>     sshl v17.4s, v16.4s, v19.4s
>>     neg v18.16b, v20.16b       # on aarch64, vector right shift is implemented as left shift by negative shift count
>>     ushl v16.4s, v16.4s, v18.4s
>>     orr v16.16b, v17.16b, v16.16b
>> 
>> With this patch, immediate vector rotation can be matched alone and optimized on CPUs like aarch64.
>> 
>> Verified with linux-x86_64-server-fastdebug tier1-3 and passed.
>> Also added immediate vector rotation tests to micro `test/micro/org/openjdk/bench/java/lang/RotateBenchmark.java`.
>> Tested the micro on a x86_64/aarch64 server and witnessed no regressions.
>
> Dong Bo has refreshed the contents of this pull request, and previous commits have been removed. The incremental views will show differences compared to the previous content of the PR.

src/hotspot/cpu/x86/x86.ad line 1817:

> 1815: }
> 1816: 
> 1817: bool Matcher::supports_vector_variable_rotates(VectorNode *n) {

Please, turn it into a capability check (just `bool Matcher::supports_vector_variable_rotates(void)`, no argument).
There's no need to wrap `Matcher::match_rule_supported_vector` since you already check it:
(in(2)->is_Con() && !Matcher::supports_vector_variable_rotates(this)) ||
!Matcher::match_rule_supported_vector(Op_RotateLeftV, vlen, bt)) {

Otherwise, looks good.

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PR: https://git.openjdk.java.net/jdk/pull/1532