Re: [omr-dev] ResolvedMethod question

["Mark Stoodley" <mstoodle@xxxxxxxxxx>]

DefineFunction is used by JitBuilder to
look up the target whenever you Call something. That can be anything with
a native entry point.

The OMR compiler and JitBuilder do not,
in and of themselves,"remember" targets that you have compiled
before, though they can handle a self-recursive function call. The code
is stored in the code cache, but the JIT "forgets" about the
entry point. That's not 100% ideal, though. In order to support "freeing"
a compiled code body, it probably should retain some meta-data about code
regions in the code cache, but it currently doesn't. 

To call something else, the OMR compiler
requires a ResolvedMethod describing the target that's able to answer simple
questions about it. The purpose of JitBuilder's DefineFunction API is to
create such ResolvedMethods for the targets of calls needed by the MethodBuilder
and to then hide the ResolvedMethods behind a name (C string) so Call can
look them up also using the simple string.

The JIT compiler does not typically
hang onto ResolvedMethods outside of a compilation. It's assumed there
are other data structures already maintaining that info (along with lots
of other stuff the JIT doesn't tend to care as much about). They are part
of the compiler specific data structures that provide a layer of indirection
across different language runtimes so that the JIT can compile code for
different runtimes even though they don't all use the same underlying structure
to represent "methods" (or functions or their equivalent concept
in other languages).

Mark Stoodley		8200 Warden Avenue
Senior Software Developer		Markham, L6G 1C7
IBM Runtime Technologies		Canada
Phone:	+1-905-413-5831
e-mail:	mstoodle@xxxxxxxxxx
We cannot solve our problems with the same thinking we used when we created them - Albert Einstein