RFR: 8339205: Optimize StackMapGenerator$Frame

[Shaojin Wen]

On Wed, 28 Aug 2024 22:38:11 GMT, Chen Liang <liach at openjdk.org> wrote:

>> A small optimization to reduce the code size of StackMapGenerator.Frame's pushStack and setLocalsFromArg methods
>> 
>> Below is the compiler log of C2
>> 
>> 
>> # baseline
>> jdk.internal.classfile.impl.StackMapGenerator$Frame::pushStack (27 bytes)   failed to inline: callee uses too much stack
>> jdk.internal.classfile.impl.StackMapGenerator$Frame::pushStack (46 bytes)   failed to inline: callee is too large
>> jdk.internal.classfile.impl.StackMapGenerator$Frame::pushStack (183 bytes)   failed to inline: callee is too large
>> jdk.internal.classfile.impl.StackMapGenerator$Frame::setLocalsFromArg (367 bytes)   failed to inline: callee is too large
>> 
>> # current
>> jdk.internal.classfile.impl.StackMapGenerator$Frame::pushStack (26 bytes)   inline
>> jdk.internal.classfile.impl.StackMapGenerator$Frame::pushStack (37 bytes)   failed to inline: callee is too large
>> jdk.internal.classfile.impl.StackMapGenerator$Frame::pushStack (82 bytes)
>> jdk.internal.classfile.impl.StackMapGenerator$Frame::setLocalsFromArg (255 bytes)   failed to inline: callee is too large
>
> src/java.base/share/classes/jdk/internal/classfile/impl/StackMapGenerator.java line 1060:
> 
>> 1058:                 if (desc == CD_void) throw new AssertionError("Should not reach here");
>> 1059:                 Type type;
>> 1060:                 if (desc instanceof PrimitiveClassDescImpl) {
> 
> Can we use `desc.isPrimitive()`?

I have tried isPrimitive(). The codeSize of the virtual function call isPrimitive() is 2 bytes larger than instanceof. The performance of instanceof should be better. But isPrimitive() is a public API and easier to understand. If you think isPrimitive is better, I think it's OK too.

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PR Review Comment: https://git.openjdk.org/jdk/pull/20756#discussion_r1735374088