RFR: 8338532: Speed up the ClassFile API MethodTypeDesc#ofDescriptor

[Chen Liang]

On Fri, 16 Aug 2024 08:53:38 GMT, Shaojin Wen <duke at openjdk.org> wrote:

> The current implementation of ofDescriptor puts return type and parameter types together in an ArrayList, and then splits them into return type and array of parameter types. This ArrayList creation is unnecessary, considering most descriptors only have few parameter types.
> 
> By splitting return type and parameter types separately and scanning the descriptor first to get the number of parameters, we can just allocate an exact, trusted array for the resulting MethodTypeDesc without copy.

src/java.base/share/classes/jdk/internal/constant/ConstantUtils.java line 297:

> 295:         String objectDesc = "Ljava/lang/Object;";
> 296:         if (len == objectDesc.length() && descriptor.regionMatches(start, objectDesc, 0, len)) {
> 297:             return ReferenceClassDescImpl.CD_Object;

Is there a reason we cannot use `ConstantDescs.CD_Object` and have to redefine it in `ReferenceClassDescImpl`? I see no dependency in initialization order, and the field in RCDI can be removed.

src/java.base/share/classes/jdk/internal/constant/MethodTypeDescImpl.java line 129:

> 127:         var returnType = resolveClassDesc(descriptor, rightBracket + 1, retTypeLength);
> 128:         if (length == 3 && returnType == CD_void) {
> 129:             return (MethodTypeDescImpl) java.lang.constant.ConstantDescs.MTD_void;

Please import instead of fully qualify ConstantDescs for this field.

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PR Review Comment: https://git.openjdk.org/jdk/pull/20611#discussion_r1722374908
PR Review Comment: https://git.openjdk.org/jdk/pull/20611#discussion_r1722375904