dustincampbell/ifvm

ifvm's Issues

It should be possible to set the memory size smaller than the current size

The Glulx spec states that it is allowable for memory size to be set to a value smaller the current size, so long as it isn't smaller than the initial size. At the moment, this isn't possible. The memory size can only grow.

Optimization: Constant folding

Arithmetic operations involving constants can be pre-computed. Consider the following set of instructions.

local_4 <- read.4(1c600 + 14)
write.4(1c600 + 14) <- read.4(1c600 + 10)
write.4(1c600 + 10) <- local_1
local_5 <- read.4(1c600 + 18)

The arithmetic operations can be pre-computed like so:

local_4 <- read.4(1c614)
write.4(1c614) <- read.4(1c610)
write.4(1c610) <- local_1
local_5 <- read.4(1c618)

Optimization: Minimize stack usage

Often, instructions will be created to push several values onto the stack just to immediately pop them off again.

For example:

push 0
push 1
push (local_8 - 4)
push (local_9 + 4)
push 43
local_4 <- call 114fe (pop, pop, pop, pop, pop)

Can be rewritten to not use the stack at all:

local_4 <- call 114fe (43, local_9 + 4, local_8 - 4, 1, 0)