RFR: 8339576: Speed up raw bytecode processing in ClassFile API

[Shaojin Wen]

On Thu, 5 Sep 2024 13:40:51 GMT, Claes Redestad <redestad at openjdk.org> wrote:

>> C2 needs 10000 calls to inline this method, so wenshao is worried. However, this method call is almost always followed by a huge switch to handle different opcode, so I doubt how much of a difference inlining brings.
>> 
>> But wenshao discovered that this method has too many field gets; I should indeed convert them to local variable access if possible.
>
> Yes, things like storing `endBci()` to a local variable can be great if it both reduces code size and improves interpreter/C1 speed - but don't over-do it as it's likely never-ending work for a kind of optimizations leyden might make pointless.

It is not necessary to use RawBytecodeHelper in the StackMapGenerator#detectFrameOffsets method. It may be better to operate directly on the `byte[] bytecode`.

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PR Review Comment: https://git.openjdk.org/jdk/pull/20863#discussion_r1745608455