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Optimise away a memory copy for returned structs in simple cases

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Brian Carroll 2021-09-17 21:49:21 +01:00
parent 4f55b7a56e
commit 52a56bfa27
2 changed files with 12 additions and 6 deletions
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10
compiler/gen_wasm/src/backend.rs
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@ -192,9 +192,15 @@ impl<'a> WasmBackend<'a> {
fn build_stmt(&mut self, stmt: &Stmt<'a>, ret_layout: &Layout<'a>) -> Result<(), String> {
match stmt {
// This pattern is a simple optimisation to get rid of one local and two instructions per proc.
// If we are just returning the expression result, then don't SetLocal and immediately GetLocal
// Simple optimisation: if we are just returning the expression, we don't need a local
Stmt::Let(let_sym, expr, layout, Stmt::Ret(ret_sym)) if let_sym == ret_sym => {
let wasm_layout = WasmLayout::new(layout);
if let WasmLayout::StackMemory { .. } = wasm_layout {
// Map this symbol to the first argument (pointer into caller's stack)
// Saves us from having to copy it later
let storage = SymbolStorage(LocalId(0), wasm_layout);
self.symbol_storage_map.insert(*let_sym, storage);
}
self.build_expr(let_sym, expr, layout)?;
self.instructions.push(Return);
Ok(())