RFR: 8315771: [JVMCI] Resolution of bootstrap methods with int[] static arguments [v11]

[Paul Sandoz]

On Tue, 19 Sep 2023 11:37:09 GMT, Sacha Coppey <duke at openjdk.org> wrote:

>> Currently, `jdk.vm.ci.meta.ConstantPool.lookupBootstrapMethodInvocation` does not support static arguments of type `int[]`.
>> 
>> Supporting those static arguments allows to correctly lookup the `BootstrapMethodInvocation` of some `InvokeDynamic` and `DynamicConstant`.
>> 
>> To lookup the constant at the index in the static arguments index list, a new class is introduced, allowing to lazily resolve the constant or obtain the constant pool index of the arguments:
>> 
>> 
>>     static class CachedBSMArgs extends AbstractList<JavaConstant> {
>>         private final JavaConstant[] cache;
>>         private final HotSpotConstantPool cp;
>>         private final int bssIndex;
>> 
>>         CachedBSMArgs(HotSpotConstantPool cp, int bssIndex, int size) {
>>             this.cp = cp;
>>             this.bssIndex = bssIndex;
>>             this.cache = new JavaConstant[size];
>>         }
>> 
>>         @Override
>>         public JavaConstant get(int index) {
>>             JavaConstant res = cache[index];
>>             if (res == null) {
>>                 int argCpi = compilerToVM().bootstrapArgumentIndexAt(cp, bssIndex, index);
>>                 res = compilerToVM().lookupConstantInPool(cp, argCpi, false);
>>                 if (res == null) {
>>                     res = JavaConstant.forInt(argCpi);
>>                 }
>>                 cache[index] = res;
>>             }
>>             return res;
>>         }
>> 
>>         @Override
>>         public int size() {
>>             return cache.length;
>>         }
>>     }
>
> Sacha Coppey has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Add an extra run configuration for TestDynamicConstant instead of replacing it

This generally looks good to me. I was initially confused about the reuse (or overload?) of `PrimitiveConstant` for a static argument that is the constant pool index to a `CONSTANT_Dynamic_info` entry, from which it can be resolved or it's `BootstrapMethodInvocation` obtained.

It's very subtle, and I wondering if using a new type would be better and more clearly distinguish between a primitive constant and an index in the constant pool. However, i am not an expert in JVMCI so do not know what repercussions that might have. It's as if you want to expose a lazily resolved constant.

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PR Comment: https://git.openjdk.org/jdk/pull/15588#issuecomment-1726691490