Project

Directory Structure

test repository contains test code

Project progress

• Evaluation by register and stack - done
• Optimization to detect which register cost - not started

Temporary Register State

The states of registers for temporary values are no longer important in the following situation.

1. Between instructions.
2. Between each argument of a function call.

Implementation

The call to tr_expr means to evaluate the expresion begining from the first register. we call tr_expr at tr_instr.

For the argument evaluation, we call aux 0 arg for each argument, which is equivlent.

Mixing Registers and the Stack

Strategy

In mips.ml, expression_registers defines available registers for temporary values, they are $t2 ~ $t7.

There's a function t: int -> register to simplify the access, so (t 0) will give us $t2.

Register $t0 and $t1 are preserved to

1. hold intermiedirea values from stack while evaluate a binary operation.
2. other occasional values.

No assupetions on these 2 registers.

Implemation

Within the tr_expr function, there are 2 functions, aux and aux_stack.

Function aux_stack translates expression only by stack, the detail will be explain later.

Function aux is responsible for implementation of registers manage and call for aux_stack when no register available. The return of aux is a tuple: (code, count), code contains mips code, count is the number of register comsumed for this expression. aux calls itself for sub-expressions.

Binary expression

Strategy

While evaluate binary expression, the register for the first operand will be used for the final result, so that each a binary operation consumes 2 registers instead of 3.

While using the stack, $t0 and $t1 are for intermediare value.

Implementation

the Binop branch of aux function

Register state among function call.

Strategy

While enconter a function call:

1. push all used registers ($t2 ~ $t7) to stack.
2. push arguments, make the call.
3. retrive return value from (t 0), save to $t0.
4. clear argument.
5. restore used registers.
6. put return value to the register for current expression.

Implementation

the Call branch of aux function.

When registers are full

Strategy

when no registers availables, all intermediare data will be store to the stack.

The function call becomes simpler in this situation, as the value of each argument is already in the stack after evaluation.

Implementation

Function aux_stack is responsible for the implmentation, it will be called by aux when there are no register available.