[jdk18] RFR: 8278508: Enable X86 maskAll instruction pattern for 32 bit JVM. [v2]

[Jatin Bhateja]

On Sat, 18 Dec 2021 00:16:35 GMT, Sandhya Viswanathan <sviswanathan at openjdk.org> wrote:

>> Jatin Bhateja has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   8278508: Review comments resolution.
>
> src/hotspot/cpu/x86/c2_MacroAssembler_x86.cpp line 4281:
> 
>> 4279:     if (mask_len > 32) {
>> 4280:       kmovql(dst, src);
>> 4281:       kshiftrql(dst, dst, 64 - mask_len);
> 
> Here masklen is 64, so kshiftrql is not needed here?

src operand carry either a 0 (false mask) or 0XFFFFFFFFFFFFFFFF  (true mask) value. Thus a right shift here ensures that destination bits whose size matches with mask_len are set.

I have introduced special case handling when mask_len is  64, 32 and 16.

> src/hotspot/cpu/x86/c2_MacroAssembler_x86.cpp line 4299:
> 
>> 4297:   kshiftlql(dst, tmp, 32);
>> 4298:   korql(dst, dst, tmp);
>> 4299:   kshiftrql(dst, dst, 64 - mask_len);
> 
> Do we need the kshiftrql here? The masklen is 64 here.
> You could alternatively use:
>    kmovdl dst, src
>    kunpckdq dst, dst, dst

DONE

> src/hotspot/cpu/x86/x86.ad line 9457:
> 
>> 9455:   predicate(Matcher::vector_length(n) <= 32);
>> 9456:   match(Set dst (MaskAll cnt));
>> 9457:   effect(TEMP dst, TEMP tmp);
> 
> TEMP dst is not needed here.

dst is both read and written to in macro assembly routine.

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PR: https://git.openjdk.java.net/jdk18/pull/24