Struct WriteTransforming

pub struct WriteTransforming;

A pass to rewrite assignments to array accesses and struct accesses.

This pass makes variables for members of arrays and structs that are written to, changes assignments to those members into assignments to those variables, and, whenever the arrays or structs are accessed, reconstructs them from the variables. So code like this:

let s = S { a: 1u8, b: [2u8, 3u8] }; s.a = 1u8; s.b[0u8] = 4u8; return s;

will be changed into something like this:

let s_a = 1u8; let s_b_0 = 2u8; let s_b_1 = 3u8; s_b_1 = 4u8; return S { a: s_a, b: [s_b_0, s_b_1] };

The pass requires that the AST is in SSA form (so that sub-expressions are always variables or literals) and that tuples have been destructured. Since the pass will create new assignments, SsaForming must be run again afterwards.

A note on the semantics of the language as implemented by this pass: assignments and definitions in essence copy structs and arrays. Thus if we do

let x = [0u8, 1u8];
let y = x;
y[0u8] = 12u8;

x is still [0u8, 1u8];

Trait Implementations

impl Pass for WriteTransforming

const NAME: &str = "WriteTransforming"

type Input = ()

type Output = ()

fn do_pass( _input: Self::Input, state: &mut CompilerState, ) -> Result<Self::Output>

Runs the compiler pass.