nested_expr.rs

use crate::ast::parse_ast::*;
use global_counter::global_counter;

/*
This file is used to "flatten" every statement in the program.
Expr can currently be nested. Netlists cannot be nested, so the tree will need to be
flattened at some point. As it makes the tree simpler to process, it is better done
close to the beginning.
The functions in this file transform :
a = 1 + 0 * b + f(0)

in:
x = 0*b
y = 1 + x
z = f(0)
a = y + z

(the names x, y, z are actually generated using the # character,
which is a forbidden character for variables names to avoid conflicts, and a global counter.)
(the $ character will be used instead for funtion and automaton calls,
with tracking information embedded inside the name)
*/
//the global counter
global_counter!(FLATTEN_EXPR_COUNTER, u32, 0);

//wrapper function to call the other functions on every statement in the program
pub fn flatten(prog: &mut Program) {
    //statements in functions
    for (_, f) in prog.functions.iter_mut() {
        f.statements = f
            .statements
            .drain(..)
            .flat_map(|stat| {
                let (v, r) = (Some(flatten_statement(stat).into_iter().map(|s| s)), None);
                v.into_iter().flatten().chain(r)
            })
            .collect::<Vec<Statement>>();
    }
    //statements in automata
    for (_, m) in &mut prog.automata {
        for (_, state) in &mut m.states {
            let State {
                name,
                weak: _,
                statements,
                transitions,
            } = state;
            *statements = statements
                .drain(..)
                .flat_map(|stat| {
                    let (v, r) = (Some(flatten_statement(stat).into_iter().map(|s| s)), None);
                    v.into_iter().flatten().chain(r)
                })
                .collect::<Vec<Statement>>();
            //transition must be handled as well.
            //They are flattened into statements in the end of the state body
            *transitions = transitions
                .drain(..)
                .map(|transition| {
                    //important to avoid creating cycles by taking shared vars out of transitions.
                    if let Expr::Var(_) = transition.condition.unwrap_ref() {
                        return transition;
                    }
                    let pos = transition.condition.loc;
                    let (mut v, expr) = flatten_expr(
                        name,
                        Loc::new(
                            transition.condition.loc,
                            transition.condition.value.unwrap(),
                        ),
                    );
                    statements.append(&mut v);
                    let name = get_name(name);
                    statements.push(Statement::Assign(vec![VarAssign {
                        var: Loc::new(pos, name.clone()),
                        expr: Loc::new(pos, expr),
                    }]));
                    Transition {
                        condition: Loc::new(pos, TrCond::Expr(Expr::Var(Loc::new(pos, name)))),
                        ..transition
                    }
                })
                .collect::<Vec<Transition>>();
        }
    }
}
//transforms a statement with a potentially nested expression inside into multiple statements
fn flatten_statement(statement: Statement) -> Vec<Statement> {
    match statement {
        Statement::Assign(mut var_assign) => {
            let mut res = Vec::new();
            for assign in var_assign.drain(..) {
                let name = assign.var.value.clone();
                let expr_pos = assign.expr.loc;
                let (mut statements, expr_out) = flatten_expr(&name, assign.expr);
                res.append(&mut statements);
                res.push(Statement::Assign(vec![VarAssign {
                    expr: Loc::new(expr_pos, expr_out),
                    var: assign.var,
                }]))
            }
            res
        }
        Statement::If(IfStruct {
            condition,
            mut if_block,
            mut else_block,
        }) => {
            let v1 = if_block.drain(..).flat_map(|stat| {
                let (v, r) = (Some(flatten_statement(stat).into_iter().map(|s| s)), None);
                v.into_iter().flatten().chain(r)
            });
            let v2 = else_block.drain(..).flat_map(|stat| {
                let (v, r) = (Some(flatten_statement(stat).into_iter().map(|s| s)), None);
                v.into_iter().flatten().chain(r)
            });
            vec![Statement::If(IfStruct {
                condition: condition,
                if_block: v1.collect::<Vec<Statement>>(),
                else_block: v2.collect::<Vec<Statement>>(),
            })]
        }
        Statement::FnAssign(mut fn_assign) => {
            let pos = fn_assign.f.name.loc;
            let fn_name = fn_assign.f.name.value.clone();
            let mut res = Vec::new();
            fn_assign.f.args = Loc::new(
                pos,
                fn_assign
                    .f
                    .args
                    .drain(..)
                    .map(|a| {
                        let (mut stmts, e_out) = flatten_expr(&fn_name, a.clone());
                        res.append(&mut stmts);
                        Loc::new(a.loc, e_out)
                    })
                    .collect::<Vec<Loc<Expr>>>(),
            );
            res.push(Statement::FnAssign(fn_assign));
            res
        }
        Statement::ExtAutomaton(_) => {
            panic!("Should not happen: nested automaton after they are collapsed")
        }
    }
}

//generates a name
fn get_name(name: &String) -> String {
    let counter = FLATTEN_EXPR_COUNTER.get_cloned();
    FLATTEN_EXPR_COUNTER.inc();
    format!("{}#flatten#{}", name, counter)
}

//takes a variable name and an expression as an arg, returns a variable and statements,
//such that if the statements are computed first then the variable contains the value of the expr
fn flatten_expr(name: &String, expr: Loc<Expr>) -> (Vec<Statement>, Expr) {
    let mut res = Vec::new();
    let glob_pos = expr.loc;
    let e_ret = match expr.value {
        Expr::Const(_) | Expr::Var(_) => expr.value,
        Expr::Last(v) => {
            let name = Loc::new(v.loc, get_name(&v.value));
            res.push(Statement::Assign(vec![VarAssign {
                var: name.clone(),
                expr: Loc::new(glob_pos, Expr::Last(v)),
            }]));
            Expr::Var(name)
        }
        Expr::FnCall(mut fn_call) => {
            let name = Loc::new(glob_pos, get_name(name));
            let fn_name = fn_call.name.value.clone();
            fn_call.args = Loc::new(
                glob_pos,
                fn_call
                    .args
                    .drain(..)
                    .map(|a| {
                        let (mut stmts, e_out) = flatten_expr(&fn_name, a.clone());
                        res.append(&mut stmts);
                        Loc::new(a.loc, e_out)
                    })
                    .collect::<Vec<Loc<Expr>>>(),
            );
            res.push(Statement::FnAssign(FnAssign {
                vars: vec![name.clone()],
                f: fn_call,
            }));
            Expr::Var(name)
        }
        Expr::Not(e_in) => {
            let (mut v, e_out) = flatten_expr(name, Loc::new(expr.loc, *e_in));
            let name = Loc::new(expr.loc, get_name(name));
            res.append(&mut v);
            res.push(Statement::Assign(vec![VarAssign {
                var: name.clone(),
                expr: Loc::new(expr.loc, Expr::Not(Box::new(e_out))),
            }]));
            Expr::Var(name)
        }
        Expr::Slice(e_in, c1, c2) => {
            let pos = e_in.loc;
            let (mut v, e_out) = flatten_expr(name, *e_in);
            let name = Loc::new(expr.loc, get_name(name));
            res.append(&mut v);
            res.push(Statement::Assign(vec![VarAssign {
                var: name.clone(),
                expr: Loc::new(
                    expr.loc,
                    Expr::Slice(Box::new(Loc::new(pos, e_out)), c1, c2),
                ),
            }]));
            Expr::Var(name)
        }
        Expr::BiOp(op, e1, e2) => {
            let pos1 = e1.loc;
            let pos2 = e2.loc;
            let (mut v1, e_out1) = flatten_expr(name, *e1);
            let (mut v2, e_out2) = flatten_expr(name, *e2);
            let name = Loc::new(pos1, get_name(name));
            res.append(&mut v1);
            res.append(&mut v2);
            res.push(Statement::Assign(vec![VarAssign {
                var: name.clone(),
                expr: Loc::new(
                    pos1,
                    Expr::BiOp(
                        op,
                        Box::new(Loc::new(pos1, e_out1)),
                        Box::new(Loc::new(pos2, e_out2)),
                    ),
                ),
            }]));
            Expr::Var(name)
        }
        Expr::Mux(e1, e2, e3) => {
            let pos1 = e1.loc;
            let pos2 = e2.loc;
            let pos3 = e3.loc;
            let (mut v1, e_out1) = flatten_expr(name, *e1);
            let (mut v2, e_out2) = flatten_expr(name, *e2);
            let (mut v3, e_out3) = flatten_expr(name, *e3);
            let name = Loc::new(glob_pos, get_name(name));
            res.append(&mut v1);
            res.append(&mut v2);
            res.append(&mut v3);
            res.push(Statement::Assign(vec![VarAssign {
                var: name.clone(),
                expr: Loc::new(
                    glob_pos,
                    Expr::Mux(
                        Box::new(Loc::new(pos1, e_out1)),
                        Box::new(Loc::new(pos2, e_out2)),
                        Box::new(Loc::new(pos3, e_out3)),
                    ),
                ),
            }]));
            Expr::Var(name)
        }
        Expr::Reg(c, e_in) => {
            let (mut v, e_out) = flatten_expr(name, Loc::new(expr.loc, e_in.value));
            let name = Loc::new(e_in.loc, get_name(name));
            res.append(&mut v);
            res.push(Statement::Assign(vec![VarAssign {
                var: name.clone(),
                expr: Loc::new(expr.loc, Expr::Reg(c, Box::new(Loc::new(e_in.loc, e_out)))),
            }]));
            Expr::Var(name)
        }
        Expr::Ram(RamStruct {
            read_addr: e1,
            write_enable: e2,
            write_addr: e3,
            write_data: e4,
        }) => {
            let pos1 = e1.loc;
            let pos2 = e2.loc;
            let pos3 = e3.loc;
            let pos4 = e4.loc;
            let (mut v1, e_out1) = flatten_expr(name, *e1);
            let (mut v2, e_out2) = flatten_expr(name, *e2);
            let (mut v3, e_out3) = flatten_expr(name, *e3);
            let (mut v4, e_out4) = flatten_expr(name, *e4);
            let name = Loc::new(pos1, get_name(name));
            res.append(&mut v1);
            res.append(&mut v2);
            res.append(&mut v3);
            res.append(&mut v4);
            res.push(Statement::Assign(vec![VarAssign {
                var: name.clone(),
                expr: Loc::new(
                    pos1,
                    Expr::Ram(RamStruct {
                        read_addr: Box::new(Loc::new(pos1, e_out1)),
                        write_enable: Box::new(Loc::new(pos2, e_out2)),
                        write_addr: Box::new(Loc::new(pos3, e_out3)),
                        write_data: Box::new(Loc::new(pos4, e_out4)),
                    }),
                ),
            }]));
            Expr::Var(name)
        }
        Expr::Rom(RomStruct {
            word_size,
            read_addr,
        }) => {
            let pos = read_addr.loc;
            let (mut v, e_out) = flatten_expr(name, *read_addr);
            let name = Loc::new(pos, get_name(name));
            res.append(&mut v);
            res.push(Statement::Assign(vec![VarAssign {
                var: name.clone(),
                expr: Loc::new(
                    pos,
                    Expr::Rom(RomStruct {
                        read_addr: Box::new(Loc::new(pos, e_out)),
                        word_size,
                    }),
                ),
            }]));
            Expr::Var(name)
        }
    };
    (res, e_ret)
}