RFR: 8343933: Add a MemorySegment::fill benchmark with varying sizes

[Per Minborg]

On Mon, 11 Nov 2024 13:59:38 GMT, Francesco Nigro <duke at openjdk.org> wrote:

> Thanks @minborg for this :) Please remember to add the misprediction count if you can and avoid the bulk methods by having a `nextMemorySegment()` benchmark method which make a single fill call site to observe the different segments (types).
> 
> Having separate call-sites which observe always the same type(s) "could" be too lucky (and gentle) for the runtime (and CHA) and would favour to have a single address entry (or few ones, if we include any optimization for the fill size) in the Branch Target Buffer of the cpu.

I've added a "mixed" benchmark. I am not sure I understood all of your comments but given my changes, maybe you could elaborate a bit more?

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PR Comment: https://git.openjdk.org/jdk/pull/22010#issuecomment-2468362180