RFR: 8255720: Optimize bci_to_dp/-data by enabling iteration over raw DataLayouts

[Tobias Hartmann]

On Sun, 1 Nov 2020 22:50:39 GMT, Claes Redestad <redestad at openjdk.org> wrote:

> MethodData::bci_to_dp and ciMethodData::bci_to_data show up in startup/warmup profiles - much of the overhead allocating resource objects when iterating over ProfileData objects (next_data)
> 
> Providing a means to iterate over the raw DataLayout objects allow us to avoid explicitly allocating resource objects for purposes of calculating the next DataLayout address for the most common types. 
> 
> This patch reduces overhead of MethodData::bci_to_dp and ciMethodData::bci_to_data by 80% or more in profiles and has a measurable impact on simple startup tests, e.g. ~250k instruction (~0.2% of total) reduction on Hello World.
> 
> Testing: tier1-3 passed

Looks good to! Some of the code formatting could be improved though (missing new lines between method definitions).

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Marked as reviewed by thartmann (Reviewer).

PR: https://git.openjdk.java.net/jdk/pull/988