rrthomas / mijit-beetle Goto Github PK

Caused by rust-lang/compiler-builtins#443, fixed in Rust 1.59 (with a bit of luck!).

Importing from Mijit #5.

The code() method of vm::machine::Machine has unnecessary complexity in a number of ways:

• The code for Lshift and Rshift differs only in one BinaryOp.

• The following code sequence is common, and could be abbreviated:

  b.load_global(<reg>, <global>);
  b.const_binary(<op>, <reg>, <reg>, <constant>);
  b.store_global(<reg>, <global>);
  

  Usually, <op> is Add and <constant> is cell_bytes(<int>).

• The following code sequence is common, and could be abbreviated:

  b.const_binary(Add, <reg>, <value>, cell_bytes(<n>));
  b.load(RD, <reg>);
  

• Code to increment B_EP and jump to Root is common. It occurs in: Qbranch, Loop.

• The code for Ploopp and Ploopm appears to be identical.

• The code for Ploopip and Ploopim appears to be identical.

• The code for Ploop and Ploopi differs only in the States they jump to.

• The difference between instructions and their i variant are very small and could be parametrized. This occurs in: Qbranch, Loop, Ploop.

• The difference between 0, 1, -1, CELL and -CELL could be parametrized.

• The difference between the various unary operators could be parametrized.

• The difference between the various binary operators could be parametrized.

• The difference between the various item op constant operators could be parametrized.

• The difference between the various constant op item operators could be parametrized.

• The difference between the various <reg>@ operators could be parametrized.

• The difference between the various <reg>! operators could be parametrized.

Currently Mijit Beetle can be used as a stand-alone virtual machine. However, it is limited and possibly buggy, and nobody is using it that way. Maybe in the future we will want to write Rust Beetle, but for now the main use of Mijit Beetle is as part of C Beetle. Therefore, focus on that use case.

1. Delete main.rs.
2. Pass M0 and the pointer to the register struct as extra arguments to mijit_beetle_run() or mijit_beetle_init().
3. Delete struct AllRegisters (leaving only struct Registers) and use three extra Globals e.g. as follows:
   • Global(1) is M0.
   • Global(2) is R2.
   • Global(3) is R3.
4. Remove the dependency of lib.rs on struct VM, by reimplementing it in terms of machine directly. This basically involves inlining the methods of VM into their callers.
5. Reverse the nesting of mod vm and mod machine and annotate mod vm with #[cfg(test)].