RFR: 8315771: [JVMCI] Resolution of bootstrap methods with int[] static arguments [v9]

[Paul Sandoz]

On Thu, 14 Sep 2023 12:48:13 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:
> 
>   Update getStaticArguments documentation example and update TestDynamicConstant to test the new functionality

Some general comments:

- Consider also running `TestDynamicConstant` with the `-XX:UseBootstrapCallInfo=3`. This will stress test the lazy resolution, so it is always lazy. See https://github.com/openjdk/jdk/blob/master/src/hotspot/share/interpreter/bootstrapInfo.cpp#L130 for more details.

- In the default case, lazy resolution of bootstrap args will only occur when a condy refers to another condy, it is not specific to primitive constants. This is to avoid an edge case of infinite recursion in HotSpot (see test https://github.com/openjdk/jdk/blob/master/test/jdk/java/lang/invoke/condy/CondyNestedTest.java)

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PR Comment: https://git.openjdk.org/jdk/pull/15588#issuecomment-1721757452