[11] RFR(M) 8201193: Use XMM/YMM for objects initialization

[John Rose]

On Jun 11, 2018, at 1:57 PM, Vladimir Kozlov <vladimir.kozlov at oracle.com> wrote:
> 
> AMD processors don't have ERMS (Enhanced REP MOVSB/STOSB) support. To have good performance it is suggested to use SSE/AVX wide registers stores instead of 'rep stosq'. It shows better performance on AMD cpus.
> 
> Tested with jdk-tier1, hs-tier1, hs-tier2, hs-precheckin-comp (-Xcomp), hs-graal on all x86 OSs. And using '-XX:-UseFastStosb -XX:+UseXMMForObjInit' flags combination to force new code generation.

Good stuff.  I have one suggestion:  If possible, let's use
macroassembler to generate the code from the AD files.
It is a maintainability problem to have three copies of
the same algorithm.  I notice in particular that the AD
file versions don't support UseAVX==1 while the assembler
does.  That's going to give some maintainer nightmares
in a few years.

— John
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