General

By mixed mode we mean that some oracle can decide if a method should be executed by the JIT (/AOT runtime) or interpreter. The default oracle is: If a method is available as AOT'd method, execute this, otherwise fall back to the interpreter. Example: On iOS we cannot JIT, therefore we have FullAOT. It can't handle System.Reflection.Emit (SRE) though, so those methods will be executed by the interpreter.

Oracles

AOT Oracle

The current supported mode works like this:

1. AOT compile assemblies with --aot=full,interp
2. execute runtime with --full-aot --interp

Currently, this isn't tested very well.

Hardcoded Oracle

We can force the interpreter with --interp=interp-only=SomeClassName for a specific class, or force the JIT with --interp=jit=SomeClassName the other way around. This is used by the mixed mode regression test:

We should extend this mode so that we can for example specify namespaces.

Hash Oracle

In order to stress test the mixed mode transitions, we should have a mode that decides seemingly randomly, but in a deterministic fashion. This can be achieved by using a hash-function for a method and a seed, for example:

gboolean use_interp = (hash(method) ^ seed) / (double)INT_MAX > 0.5

Plan for testing

• JIT (BCL) + interp with extended hardcoded oracle

  JIT + interp with hash oracle. Not sure yet if this will be suitable for CI, but definitely useful for stress testing locally.

  FullAOT (BCL) + interp with with default oracle

  FullAOT+LLVM (BCL) + interp with default oracle
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