[foreign-memaccess+abi] RFR: 8275647: Enable multi-register return values for optimized upcall stubs

[Jorn Vernee]

On Tue, 2 Nov 2021 19:07:45 GMT, Jorn Vernee <jvernee at openjdk.org> wrote:

> Hi,
> 
> After we've added multi-register return support to native invokers, this patch does the same for optimized upcall stubs. The strategy is very similar: the caller (in this case the upcall stub) allocates a return buffer in which the return values are stored, and then after the upcall shuffles the return values from the buffer into the right registers.
> 
> This patch also removes the buffered invocation strategy for upcalls, and all related code, such as BufferLayout.
> 
> ~Note, in it's current state this patch will disable regress AArch64 since optimized upcalls are not implemented there yet. i.e. this PR is blocked by: https://bugs.openjdk.java.net/browse/JDK-8275646~
> 
> Jorn

src/hotspot/cpu/x86/universalUpcallHandler_x86_64.cpp line 314:

> 312:   // skip receiver
> 313:   BasicType* in_sig_bt = out_sig_bt + 1;
> 314:   int total_in_args = total_out_args - 1;

I've moved this to the shared code in universalUpcallHanlder.cpp, since it can be shared between platforms.

src/hotspot/share/code/codeBlob.cpp line 759:

> 757:   JNIHandles::destroy_global(blob->receiver());
> 758:   BufferBlob::free(blob);
> 759: }

We were freeing upcall stubs using CodeCache::free, but this doesn't track memory usage. I've added this method to properly handle freeing upcall stubs.

src/jdk.incubator.foreign/share/classes/jdk/internal/foreign/abi/ProgrammableUpcallHandler.java line 143:

> 141: 
> 142:         // we handle returns first since IMR adds an extra parameter that needs to be specialized as well
> 143:         if (llReturn != void.class || callingSequence.needsReturnBuffer()) {

Note that the old code for handling return values is just moved from below the code that handles arguments (and then handling for mutli-reg returns added to that), since the return buffer argument also needs to be handle along with the rest of arguments.

src/jdk.incubator.foreign/share/classes/jdk/internal/foreign/abi/ProgrammableUpcallHandler.java line 203:

> 201:                                   CallingSequence callingSequence,
> 202:                                   Binding.VMStore[] retMoves,
> 203:                                   ABIDescriptor abi) {}

Same as with downcalls, I've bundled all the extra arguments into a record.

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PR: https://git.openjdk.java.net/panama-foreign/pull/608