Use VM criteria for J2I Thunk Sharing in AOT Compiles

[dsouzai]

In a non-AOT compilation, the JIT generates J2I Thunks and stores them into a VM Hash Table using the j9ThunkNewSignature API; it looks up existing thunks using the j9ThunkLookupSignature API. In an AOT compilation, the JIT does not uses these APIs, but rather simply stores the Thunks into the SCC using the signature of the method as the key.

The VM API will share the thunks for two different methods if all of the following is true:

1. They have the same return type
2. They have the same primitive type arguments

Therefore, if two methods have different object types, they can still use the same thunk. For example, foo(IILMyObject;)V and bar(IILMyOtherObject;)V can share the same thunk, but baz(ILMyObject;I)V cannot.

Because AOT compiles only used the signature of the method as the key for the SCC entry, it resulted in thunks that could be shared not being shared. This is the root cause of the problem described in #16402.

This PR reuses the VM mechanism to encode the signature to generate the key to store the SCC entry. As such, the same sharing that occurs in a non-AOT compile will also occur in an AOT compile.

Fixes #16402

[dsouzai]

There is a future PR where findPersistentThunk will be cleaned up. At the moment, two different types of J2I thunks are stored using this, but they are maintained by completely different data structures. The future cleanup PR will address this.

[dsouzai]

@mpirvu could you please review.

@pshipton could you please review the changes in thunkcrt.c.

[mpirvu]

LGTM. I only have a couple of small requests regarding comments.
If you do any future cleanup (I saw a comment saying that you intend that) maybe it's worth creating a data structure for the thunk. I saw some magic where we get back by 8 bytes and then read the thunk code length stored on 4 bytes.

[mpirvu]

jenkins test sanity all jdk17

[mpirvu]

@dsouzai Some compilation errors:

11:03:31  /Users/jenkins/workspace/Build_JDK17_x86-64_mac_Personal/openj9/runtime/codert_vm/thunkcrt.c:584:59: error: passing 'U_8 *' (aka 'unsigned char *') to parameter of type 'const char *' converts between pointers to integer types with different sign [-Werror,-Wpointer-sign]
11:03:31          store = vm->sharedClassConfig->storeSharedData(vmThread, encodedSignature, encodedLength, &dataDescriptor);
11:03:31                                                                   ^~~~~~~~~~~~~~~~
11:03:31  /Users/jenkins/workspace/Build_JDK17_x86-64_mac_Personal/openj9/runtime/codert_vm/thunkcrt.c:608:50: error: passing 'U_8 *' (aka 'unsigned char *') to parameter of type 'const char *' converts between pointers to integer types with different sign [-Werror,-Wpointer-sign]
11:03:31          vm->sharedClassConfig->findSharedData(vmThread, encodedSignature, encodedLength, J9SHR_DATA_TYPE_AOTTHUNK, FALSE, &dataDescriptor, NULL);
11:03:31                                                          ^~~~~~~~~~~~~~~~
11:03:31  2 errors generated.

[dsouzai]

I guess some compilers don't like encodedSignature not getting cast to a const char * :(

[dsouzai]

Since tests were already kicked off, I'll wait to force push until they're done.

zLinux build failed because of #9758

[dsouzai]

jenkins test sanity all jdk17