RFR: 8279508: Auto-vectorize Math.round API [v9]

[Sandhya Viswanathan]

On Sat, 26 Feb 2022 01:06:21 GMT, Sandhya Viswanathan <sviswanathan at openjdk.org> wrote:

>> Jatin Bhateja has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   8279508: Adding descriptive comments.
>
> src/hotspot/cpu/x86/x86.ad line 7263:
> 
>> 7261:     __ vector_round_float_avx($dst$$XMMRegister, $src$$XMMRegister, $xtmp1$$XMMRegister,
>> 7262:                               $xtmp2$$XMMRegister, $xtmp3$$XMMRegister, $xtmp4$$XMMRegister,
>> 7263:                               ExternalAddress(vector_float_signflip()), new_mxcsr, $scratch$$Register, vlen_enc);
> 
> The vector_float_signflip() here should be replaced by vector_all_bits_set().
> cvtps2dq description:
> If a converted result cannot be represented in the destination
> format, the floating-point invalid exception is raised, and if this exception is masked, the indefinite integer value
> (2w-1, where w represents the number of bits in the destination format) is returned.

Clarification, the number in my comments above is (2^w  - 1). This is from Intel SDM (https://www.intel.com/content/www/us/en/developer/articles/technical/intel-sdm.html).
Also you will need to take care when the valid unoverflowed result is -1 i.e. 0xFFFFFFFF (2^32 - 1).

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PR: https://git.openjdk.java.net/jdk/pull/7094