RFR: 8353686: Optimize Math.cbrt for x86 64 bit platforms [v3]

[Mohamed Issa]

On Tue, 27 May 2025 22:30:17 GMT, Sandhya Viswanathan <sviswanathan at openjdk.org> wrote:

>> Mohamed Issa has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   Add new set of cbrt micro-benchmarks
>
> src/hotspot/cpu/x86/macroAssembler_x86.hpp line 1251:
> 
>> 1249:   void movapd(XMMRegister dst, Address src) { Assembler::movapd(dst, src); }
>> 1250:   void movapd(XMMRegister dst, AddressLiteral src, Register rscratch = noreg);
>> 1251: 
> 
> You could write it as:
> using Assembler::movapd;
> void movapd(XMMRegister dst, AddressLiteral src, Register rscratch = noreg);

Ok, this is updated now.

> src/hotspot/cpu/x86/macroAssembler_x86.hpp line 1323:
> 
>> 1321:   void unpckhpd(XMMRegister dst, XMMRegister src) { Assembler::unpckhpd(dst, src); }
>> 1322:   void unpcklpd(XMMRegister dst, XMMRegister src) { Assembler::unpcklpd(dst, src); }
>> 1323: 
> 
> Do we need these declarations here?

No, they were superfluous as cbrt stub generator could already access them. I removed them now.

> src/hotspot/cpu/x86/stubGenerator_x86_64_cbrt.cpp line 43:
> 
>> 41: //
>> 42: // Special cases:
>> 43: //  cbrt(NaN) = quiet NaN, and raise invalid exception
> 
> No exception is raised so the comment needs to be corrected.

This is corrected now.

> src/hotspot/cpu/x86/stubGenerator_x86_64_cbrt.cpp line 226:
> 
>> 224:   __ andl(rcx, 248);
>> 225:   __ lea(r8, ExternalAddress(rcp_table));
>> 226:   __ movsd(xmm4, Address(r8, rcx, Address::times_1));
> 
> This address and other instructions using similar address could be written as  Address(rcx, r8, Address::times_1).

Ok, I have changed the order, so rcx is viewed as base and r8 is viewed as index now.

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PR Review Comment: https://git.openjdk.org/jdk/pull/24470#discussion_r2112516974
PR Review Comment: https://git.openjdk.org/jdk/pull/24470#discussion_r2112518997
PR Review Comment: https://git.openjdk.org/jdk/pull/24470#discussion_r2112520793
PR Review Comment: https://git.openjdk.org/jdk/pull/24470#discussion_r2112520486