A continuation of my exploration of the reverse linear scan regalloc algorithm (SSRA).

This project parses a program, uses my sample implementation of SSRA in the regalloc2 (https://github.com/d-sonuga/regalloc2) crate for register allocation, and outputs the program rewritten to use the physical registers.

The input program must be in the form of the sample programs in sample/.

Accepts a program:

• block to indicate blocks and block parameters.
• Virtual registers of form vn where n is the register number.
• goto for unconditional branches, with the block parameters listed in front.
• if ... goto ... else goto ... for conditional branches with 2 targets.
• Outputs output [virtual register] (Meaning read virtual register and output its value, so the operand is an early use).
• Inputs: [virtual register] = input (Meaning accept input and store it in virtual register, so the operand is a late def).
• Operations: [virtual-register] = [command] [virtual-register | constant] [virtual-register | constant], where command is a string, the virtual registers/constants following are early use operands and the virtual register on the left side of the equals sign is
• Each instruction is either a return with no arguments, an unconditional branch, a conditional branch, an output, an input, or an operation.
• Each block must end in a branch or return.
• Branches and returns must not be in the middle of a block.
• There must be no critical edges.

All values are assumed to be integers.

For example, a sample program with 8 virtual registers and 2 blocks:

block 0
    v0 = input
    v1 = input
    v2 = add v0 v1
    v3 = add v2 v1
    v4 = add v0 v3
    goto 1 v0

block 1 v5
    v6 = input
    v7 = add v5 v6
    return

A sample output with only 2 physical registers:

block 0
    p0i = input
    p1i = input
    move p0i to stack1
    p0i = add p0i p1i 
    p0i = add p0i p1i 
    move stack1 to p1i
    move p1i to stack0
    p1i = add p1i p0i 
    goto Block(1) 

block 1
    move stack0 to p1i
    p0i = input
    p1i = add p1i p0i 
    return

To run:

cargo run [input path] [no of registers]

With a sample input:

cargo run sample/input3.txt 2