RFR: 8321648: Integral gather optimized mask computation.

[Jatin Bhateja]

On Mon, 11 Dec 2023 10:33:05 GMT, Jatin Bhateja <jbhateja at openjdk.org> wrote:

>> While you are at it, you can change the `address` operand of these to only accept no-index ones, removing the need of the `lea` instruction.
>
>> While you are at it, you can change the `address` operand of these to only accept no-index ones, removing the need of the `lea` instruction.
> 
> Hi @merykitty ,  Memory patterns fold address generation components (base , index, scale) into instruction encoding thus eliminating a need to emit explicit ADD, MUL instruction sequence to compute address, saving lea may prevent folding memory patterns and may prove to be costly.

> @jatin-bhateja Could you elaborate on what the failure mode for the incorrect instruction attribution would look like? Is this just inefficient execution or would it lead to a crash?

Hi @TobiHartmann , These gather instruction are strictly applicable for AVX2 targets and will always be VEX encoded, instruction patterns corresponding to them operate on legacy vector register mask operands. Thus, this looks more of a typo error to set VL as true. Other change is for strength reduction and replacing a memory operand instruction.

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PR Comment: https://git.openjdk.org/jdk/pull/17048#issuecomment-1853497698