Implement support for indirect calls via dynexec/procref

[bitwalker]

Now that 0xPolygonMiden/miden-vm#1078 is merged (which introduces dynexec), the groundwork for supporting indirect calls in Miden Assembly is there. Before we can make use of it though, we need the proposed procref instruction, which would push the hash of a specified function name on the stack. This is done prior to dynexec, which requires that hash in order to execute the indirect call. We need procref because we don't know the hash of the function until after compilation, which procref solves by relying on the Miden assembler to expand it into push.HASH as it knows the hashes of all the functions.

Once that is implemented, we can make use of it to implement indirect calls in the IR:

Tasks

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1. Add a new call.indirect opcode, to be paired with the PrimOp instruction type
2. Add a new Type variant, Type::Function(Box<FunctionType>) which will be used in conjunction with Type::Ptr to represent function pointers
3. Add a new data segment to Program which represents every function in the compiled program as a table of hashes. Initialize this table at runtime using procref
4. Wasm tables and call_indirect op translation #133
   0 of 3
   frontend wasm +2
   
5. Lower indirect calls to MASM by treating the function pointer operand as an index into the function table, load the callee hash, and then dispatch via dynexec. Indexing beyond the bounds of the table should trap.

[bobbinth]

It might also be good to wait for 0xPolygonMiden/miden-vm#1091 - but, of course, not necessary.

[bitwalker]

Agreed, I think it is beneficial to wait for those changes, though we can at least lay the groundwork for indirect calls without supporting them in codegen. If it turns out that we reach a point where we have procref but not the changes proposed in that issue, we can experiment with what's there now, but I don't anticipate doing that unless indirect calls turn out to be more important than initially thought when compiling from Rust.

[greenhat]

@bitwalker While translating the basic wallet Wasm component example PR I found a case where table is used as a parameter for module instantiation and I want to make sure we capture these semantics in the IR.

The gist of it is that the table is defined (but not initialized) and used in module A in call_indirect ops and this table is exported from module A. Then, module B which has a table import is supplied with module A's exported table as an argument on instantiation and initializes it with references to its own (module B) imported functions (component imports). So, call_indirect op in module A is calling functions from module B's imports.

A table argument (other module's export) to a module instantiation for the module's import is concatenated on module allocation to the module's defined(local) tables.
All tables in Wasm are stored in a global store (see module instantiation) which acts as a global state (see store).

I believe we can capture these semantics in the IR by storing tables in IR Component and using their references in whatever modules they are used in after resolving all import/export relations. However, since we support the core Wasm module compilation without the Wasm component model, we need to decide how we store tables in this case. Now, Wasm core module is translated into an IR Module. I think for the sake of unification, we could wrap such IR Module with an empty Component and store tables in it.