RFR: 8341141: Optimize DirectCodeBuilder [v25]

[Claes Redestad]

On Tue, 8 Oct 2024 09:57:43 GMT, Shaojin Wen <swen at openjdk.org> wrote:

>> Some DirectCodeBuilder related optimizations to improve startup and running performance:
>> 1. Merge calls, merge writeU1 and writeU2 into writeU3
>> 2. Merge calls, merge writeU1 and writeIndex operations
>> 3. Directly use writeU1 instead of writeBytecode
>> 4. Rewrite the implementation of load and store
>
> Shaojin Wen has updated the pull request incrementally with four additional commits since the last revision:
> 
>  - Fold opcode.bytecode() in writeLoadConstant
>  - A few missed places, U1U2U2 seem common enough too to be included
>  - Rename writeUtfEntry
>  - Fold TAG_UTF8 write into writeUTF

LGTM. 

I spotted places outside of the DirectCodeBuilder paths that could benefit from using these new coalescing writers, but write-only cases is a good focus point for now.

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Marked as reviewed by redestad (Reviewer).

PR Review: https://git.openjdk.org/jdk/pull/21243#pullrequestreview-2353954741