RFR: 8287555: Tighten G1 G1BlockOffsetTable::block_start() code

[Kim Barrett]

On Fri, 24 Jun 2022 08:38:04 GMT, Thomas Schatzl <tschatzl at openjdk.org> wrote:

>> I had something like that, but the "not observable" part was not that clear in my results (i.e. during garbage collection; "not clear" as in it seems to be slower) so I only optimized the part where this can be statically determined for now.
>
> CPU resources like branch prediction/speculative execution aren't free either, and this is a very performance sensitive area of code.
> I'm planning to revisit this again for the card scanning code which in 99% of cases takes the aligned path.

Then why not just card-align addr and always use the fast path code?

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PR: https://git.openjdk.org/jdk/pull/9059