curlywas/src/constfold.rs

use crate::ast;

pub fn fold_script(script: &mut ast::Script) {
    for func in &mut script.functions {
        fold_expr(&mut func.body);
    }
}

fn fold_mem_location(mem_location: &mut ast::MemoryLocation) {
    fold_expr(&mut mem_location.left);
    fold_expr(&mut mem_location.right);
}

fn fold_expr(expr: &mut ast::Expression) {
    use ast::BinOp::*;
    match expr.expr {
        ast::Expr::Block { ref mut statements, ref mut final_expression} => {
            for stmt in statements {
                fold_expr(stmt);
            }
            if let Some(ref mut expr) = final_expression {
                fold_expr(expr);
            }        
        }
        ast::Expr::Let { ref mut value, .. } => {
            if let Some(ref mut expr) = value {
                fold_expr(expr);
            }
        }
        ast::Expr::Poke {
            ref mut mem_location,
            ref mut value,
            ..
        } => {
            fold_mem_location(mem_location);
            fold_expr(value);
        }
        ast::Expr::Peek(ref mut mem_location) => fold_mem_location(mem_location),
        ast::Expr::UnaryOp { op, ref mut value } => {
            fold_expr(value);
            let result = match (op, &value.expr) {
                (ast::UnaryOp::Negate, ast::Expr::I32Const(value)) => Some(ast::Expr::I32Const(-*value)),
                _ => None
            };
            if let Some(result) = result {
                expr.expr = result;
            }
        }
        ast::Expr::BinOp {
            ref mut left,
            op,
            ref mut right,
            ..
        } => {
            fold_expr(left);
            fold_expr(right);
            match (&left.expr, &right.expr) {
                (&ast::Expr::I32Const(left), &ast::Expr::I32Const(right)) => {
                    let result = match op {
                        Add => left.wrapping_add(right),
                        Sub => left.wrapping_sub(right),
                        Mul => left.wrapping_mul(right),
                        Div => {
                            if let Some(result) = left.checked_div(right) {
                                result
                            } else {
                                return;
                            }
                        }
                        Rem => {
                            if let Some(result) = left.checked_rem(right) {
                                result
                            } else {
                                return;
                            }
                        }
                        And => left & right,
                        Or => left | right,
                        Xor => left ^ right,
                        Eq => (left == right) as i32,
                        Ne => (left != right) as i32,
                        Lt => (left < right) as i32,
                        Le => (left <= right) as i32,
                        Gt => (left > right) as i32,
                        Ge => (left >= right) as i32,
                        Lsl => left << right,
                        Lsr => ((left as u32) >> right) as i32,
                        Asr => left >> right
                    };
                    expr.expr = ast::Expr::I32Const(result);
                }
                (&ast::Expr::F32Const(left), &ast::Expr::F32Const(right)) => {
                    use ast::Expr::*;
                    expr.expr = match op {
                        Add => F32Const(left + right),
                        Sub => F32Const(left - right),
                        Mul => F32Const(left * right),
                        Div => F32Const(left / right),
                        Rem | And | Or | Xor | Lsl | Lsr | Asr => return,
                        Eq => I32Const((left == right) as i32),
                        Ne => I32Const((left != right) as i32),
                        Lt => I32Const((left < right) as i32),
                        Le => I32Const((left <= right) as i32),
                        Gt => I32Const((left > right) as i32),
                        Ge => I32Const((left >= right) as i32),
                    };
                }
                _ => (),
            }
        }
        ast::Expr::I32Const(_) | ast::Expr::F32Const(_) | ast::Expr::Variable { .. } => (),
        ast::Expr::Assign { ref mut value, .. } => fold_expr(value),
        ast::Expr::LocalTee { ref mut value, .. } => fold_expr(value),
        ast::Expr::Loop { ref mut block, .. } => fold_expr(block),
        ast::Expr::Branch(_) => (),
        ast::Expr::BranchIf {
            ref mut condition, ..
        } => fold_expr(condition),
        ast::Expr::Cast { ref mut value, .. } => fold_expr(value),
        ast::Expr::FuncCall {
            ref name,
            ref mut params,
            ..
        } => {
            for param in params.iter_mut() {
                fold_expr(param);
            }
            use ast::Expr::*;
            let params: Vec<_> = params.iter().map(|e| &e.expr).collect();
            expr.expr = match (name.as_str(), params.as_slice()) {
                ("sqrt", [F32Const(v)]) if *v >= 0.0 => F32Const(v.sqrt()),
                _ => return,
            };
        }
        ast::Expr::Select {
            ref mut condition,
            ref mut if_true,
            ref mut if_false,
            ..
        } => {
            fold_expr(condition);
            fold_expr(if_true);
            fold_expr(if_false);
        }
        ast::Expr::If {
            ref mut condition, ref mut if_true, ref mut if_false
        } => {
            fold_expr(condition);
            fold_expr(if_true);
            if let Some(ref mut if_false) = if_false {
                fold_expr(if_false);
            }
        }
        ast::Expr::Return { value: Some(ref mut value) } => fold_expr(value),
        ast::Expr::Return { value: None } => (),
        ast::Expr::Error => unreachable!()
    }
}