32MB was just slightly too large for PowerPC immediate call instructions
to span, and 16MB matches the JIT executable memory area we use in
compile.cpp.
We now create a unique thunk for each vtable position so as to avoid
relying on using the return address to determine what method is to be
compiled and invoked, since we will not have the correct return address
in the case of a tail call. This required refactoring how executable
memory is allocated in order to keep AOT compilation working. Also, we
must always use the same register to hold the class pointer when
compiling virtual calls, and ensure that the pointer stays there until
the call instruction is executed so we know where to find it in the
thunk.
bootimage.cpp
This is useful for debugging the compiler, since it allows you to
compile one method in particular if that's where a bug manifests itself.
