RFR: 8341141: Optimize DirectCodeBuilder [v23]

[Chen Liang]

On Sat, 5 Oct 2024 16:33:50 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 one additional commit since the last revision:
> 
>   fix merge error

Everything else looks good.

src/java.base/share/classes/jdk/internal/classfile/impl/DirectCodeBuilder.java line 78:

> 76:     private static final LocalVariableType[] EMPTY_LOCAL_VARIABLE_TYPE_ARRAY = new LocalVariableType[0];
> 77:     private static final AbstractPseudoInstruction.ExceptionCatchImpl[] EMPTY_HANDLER_ARRAY = new AbstractPseudoInstruction.ExceptionCatchImpl[0];
> 78:     private static final DeferredLabel[] EMPTY_DEFERRED_LABEL_ARRAY = new DeferredLabel[0];

You used `{}` for conciseness in `DirectClassBuilder`. Maybe use `{}` here as well?

src/java.base/share/classes/jdk/internal/classfile/impl/DirectCodeBuilder.java line 507:

> 505:         } else {
> 506:             bytecodesBufWriter.writeU1U1U2(WIDE, bytecode, slot);
> 507:         }

Can we do:

        if ((slot & ~0xFF) == 0)
            bytecodesBufWriter.writeU1U1(bytecode, slot);
        else if ((slot & ~0xFFFF) == 0)
            bytecodesBufWriter.writeU1U1U2(WIDE, bytecode, slot);
        else
            throw BytecodeHelpers.slotOutOfBounds(slot);

src/java.base/share/classes/jdk/internal/classfile/impl/DirectCodeBuilder.java line 989:

> 987:     @Override
> 988:     public CodeBuilder aload(int slot) {
> 989:         if (slot >= 0 && slot <= 3) {

Should we use `if ((slot & ~3) != 0)` for shorter bytecode? #21367

-------------

PR Review: https://git.openjdk.org/jdk/pull/21243#pullrequestreview-2352814559
PR Review Comment: https://git.openjdk.org/jdk/pull/21243#discussion_r1790792835
PR Review Comment: https://git.openjdk.org/jdk/pull/21243#discussion_r1790810567
PR Review Comment: https://git.openjdk.org/jdk/pull/21243#discussion_r1790804586