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CodeBuilder doc comments

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Brian Carroll 2021-10-10 17:23:46 +01:00
parent 041e26e807
commit 58549bdf07
1 changed files with 21 additions and 5 deletions
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26
compiler/gen_wasm/src/code_builder.rs
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@ -14,11 +14,12 @@ pub enum VirtualMachineSymbolState {
NotYetPushed,
/// Value has been pushed onto the VM stack but not yet popped
/// Remember which instruction pushed it, in case we need it
/// Remember where it was pushed, in case we need to insert another instruction there later
Pushed { pushed_at: usize },
/// Value has been pushed and popped. If we want to use it again, we will
/// have to go back and insert an instruction where it was pushed
/// Value has been pushed and popped, so it's not on the VM stack any more.
/// If we want to use it again later, we will have to create a local for it,
/// by going back to insert a local.tee instruction at pushed_at
Popped { pushed_at: usize },
}
@ -28,7 +29,7 @@ pub struct CodeBuilder {
code: Vec<Instruction>,
/// Extra instructions to insert at specific positions during finalisation
/// (Mainly to go back and set locals when we realise we need them)
/// (Go back and set locals when we realise we need them)
insertions: BTreeMap<usize, Instruction>,
/// Our simulation model of the Wasm stack machine
@ -51,6 +52,7 @@ impl CodeBuilder {
self.vm_stack.clear();
}
/// Add an instruction
pub fn add_one(&mut self, inst: Instruction) {
let (pops, push) = get_pops_and_pushes(&inst);
let new_len = self.vm_stack.len() - pops as usize;
@ -64,6 +66,7 @@ impl CodeBuilder {
self.code.push(inst);
}
/// Add many instructions
pub fn add_many(&mut self, instructions: &[Instruction]) {
let old_len = self.vm_stack.len();
let mut len = old_len;
@ -86,6 +89,8 @@ impl CodeBuilder {
self.code.extend_from_slice(instructions);
}
/// Special-case method to add a Call instruction
/// Specify the number of arguments the function pops from the VM stack, and whether it pushes a return value
pub fn add_call(&mut self, function_index: u32, pops: usize, push: bool) {
let stack_depth = self.vm_stack.len();
if pops > stack_depth {
@ -107,6 +112,7 @@ impl CodeBuilder {
self.code.push(inst);
}
/// Finalize a function body by copying all instructions into a vector
pub fn finalize_into(&mut self, final_code: &mut Vec<Instruction>) {
let mut insertions_iter = self.insertions.iter();
let mut next_insertion = insertions_iter.next();
@ -130,6 +136,8 @@ impl CodeBuilder {
self.code.len() + self.insertions.len()
}
/// Set the Symbol that is at the top of the VM stack right now
/// We will use this later when we need to load the Symbol
pub fn set_top_symbol(&mut self, sym: Symbol) -> VirtualMachineSymbolState {
let len = self.vm_stack.len();
let pushed_at = self.code.len();
@ -166,6 +174,13 @@ impl CodeBuilder {
true
}
/// Load a Symbol that is stored in the VM stack
/// If it's already at the top of the stack, no code will be generated.
/// Otherwise, local.set and local.get instructions will be inserted, using the LocalId provided.
///
/// If the return value is `Some(s)`, `s` should be stored by the caller, and provided in the next call.
/// If the return value is `None`, the Symbol is no longer stored in the VM stack, but in a local.
/// (In this case, the caller must remember to declare the local in the function header.)
pub fn load_symbol(
&mut self,
symbol: Symbol,
@ -182,7 +197,8 @@ impl CodeBuilder {
match top {
Some(top_symbol) if top_symbol == symbol => {
// We're lucky, the symbol is already on top of the VM stack
// No code to generate, just let the caller know what happened
// No code to generate! (This reduces code size by up to 25% in tests.)
// Just let the caller know what happened
Some(Popped { pushed_at })
}
_ => {