olahiuj / misri

NJU irsim in rust

misri

Fast NJU IRsim written in rust, with slight modifications in instruction usage.

Up to 70x performance gains compared to the obsolete python version.

Command	Mean [s]	Min [s]	Max [s]	Relative
python ../simulator/irsim.py opt-out.ir > mine.log	6.296 ± 0.232	5.943	6.614	71.80 ± 10.64
./misri -f opt-out.ir > std.log	0.088 ± 0.013	0.070	0.101	1.00

Build & Test & Run

cargo build --release
cargo test
./misri --help

TODO

• A simple debugger
• JIT?

IR spec

This section will briefly introduce IR instructions that differ with the reference manual and the reasons for modifications.

A valid program consists of a list of functions. Each function owns a list of instructions as its body. Functions with identical names are not allowd.

FUNCTION <name> :

Variables

The reference manual requires that all variables shouldn't have the same names, while misri allows different variables from different functions to have identical names.

Arithmetic

ASSIGN

<x> := <y>

Assign the value of <y> to <x>.

BINARY

<x> := <y> <binOp> <z>

Calculate the value of <y> <binOp> <z> according to <binOp>, and stores the result to <x>.

Note

1. The behavior of a division-by-zero scenario is undefined.
2. Integer divisions always round towards zero.

Memory

DEC

DEC <x> <size>

DEC instructions are used to allocate on-stack memories, especially for arrays and structs.

The reference manual implies that <x> will hold the value of the first four bytes allocated by this instruction. For example, executing DEC x 8 results in {{x = 0}}.

This is a bit of annoying since we expect the allocation to yield a pointer to the first address of that contiguous space. Thus misri changes this behavior. DEC will return the address of the allocated memories, with the hope of simplifying subsequent procedures to handle memory accesses.

An alternative choice to achieve this could be:

DEC tmp 114  // tmp holds the first 4 bytes of 114 allocated bytes 
x := &tmp       // x now points to the starting address of the 114 bytes

DEREF

<x> := &<y>

DEREF instructions takes the address of <y>, and stores it to <x>.

The reference manual is quiet about taking the addresses of regular variables (i.e. variables that are not parts of memories allocated by DEC).

misri actually ignores dereferencing, and will perform a normal assignment. If <y> is already a pointer, <x> := &<y> will be equivalent to <x> := <y>.