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More optimizations.

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This commit is contained in:
Stephen Chung 2020-03-11 23:43:10 +08:00
parent 952932f64c
commit a02c0cfaa0
1 changed files with 95 additions and 57 deletions
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146
src/optimize.rs
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@ -1,27 +1,28 @@
use crate::engine::KEYWORD_DUMP_AST;
use crate::parser::{Expr, Stmt};
fn optimize_stmt(stmt: Stmt, changed: &mut bool) -> Stmt {
fn optimize_stmt(stmt: Stmt, changed: &mut bool, preserve_result: bool) -> Stmt {
match stmt {
Stmt::IfElse(expr, stmt1, None) => match *expr {
Expr::False(pos) => {
*changed = true;
Stmt::Noop(pos)
}
Expr::True(_) => optimize_stmt(*stmt1, changed),
Expr::True(_) => optimize_stmt(*stmt1, changed, true),
expr => Stmt::IfElse(
Box::new(optimize_expr(expr, changed)),
Box::new(optimize_stmt(*stmt1, changed)),
Box::new(optimize_stmt(*stmt1, changed, true)),
None,
),
},
Stmt::IfElse(expr, stmt1, Some(stmt2)) => match *expr {
Expr::False(_) => optimize_stmt(*stmt2, changed),
Expr::True(_) => optimize_stmt(*stmt1, changed),
Expr::False(_) => optimize_stmt(*stmt2, changed, true),
Expr::True(_) => optimize_stmt(*stmt1, changed, true),
expr => Stmt::IfElse(
Box::new(optimize_expr(expr, changed)),
Box::new(optimize_stmt(*stmt1, changed)),
Some(Box::new(optimize_stmt(*stmt2, changed))),
Box::new(optimize_stmt(*stmt1, changed, true)),
Some(Box::new(optimize_stmt(*stmt2, changed, true))),
),
},
@ -30,18 +31,18 @@ fn optimize_stmt(stmt: Stmt, changed: &mut bool) -> Stmt {
*changed = true;
Stmt::Noop(pos)
}
Expr::True(_) => Stmt::Loop(Box::new(optimize_stmt(*stmt, changed))),
Expr::True(_) => Stmt::Loop(Box::new(optimize_stmt(*stmt, changed, false))),
expr => Stmt::While(
Box::new(optimize_expr(expr, changed)),
Box::new(optimize_stmt(*stmt, changed)),
Box::new(optimize_stmt(*stmt, changed, false)),
),
},
Stmt::Loop(stmt) => Stmt::Loop(Box::new(optimize_stmt(*stmt, changed))),
Stmt::Loop(stmt) => Stmt::Loop(Box::new(optimize_stmt(*stmt, changed, false))),
Stmt::For(id, expr, stmt) => Stmt::For(
id,
Box::new(optimize_expr(*expr, changed)),
Box::new(optimize_stmt(*stmt, changed)),
Box::new(optimize_stmt(*stmt, changed, false)),
),
Stmt::Let(id, Some(expr), pos) => {
Stmt::Let(id, Some(Box::new(optimize_expr(*expr, changed))), pos)
@ -53,42 +54,67 @@ fn optimize_stmt(stmt: Stmt, changed: &mut bool) -> Stmt {
let mut result: Vec<_> = statements
.into_iter() // For each statement
.map(|s| optimize_stmt(s, changed)) // Optimize the statement
.filter(Stmt::is_op) // Remove no-op's
.rev() // Scan in reverse
.map(|s| optimize_stmt(s, changed, preserve_result)) // Optimize the statement
.enumerate()
.filter(|(i, s)| s.is_op() || (preserve_result && *i == 0)) // Remove no-op's but leave the last one if we need the result
.map(|(_, s)| s)
.rev()
.collect();
if let Some(last_stmt) = result.pop() {
// Remove all raw expression statements that evaluate to constants
// except for the very last statement
// Remove all raw expression statements that are pure except for the very last statement
let last_stmt = if preserve_result { result.pop() } else { None };
result.retain(|stmt| match stmt {
Stmt::Expr(expr) if expr.is_constant() || expr.is_identifier() => false,
Stmt::Expr(expr) if expr.is_pure() => false,
_ => true,
});
result.push(last_stmt);
if let Some(stmt) = last_stmt {
result.push(stmt);
}
// Remove all let statements at the end of a block - the new variables will go away anyway.
// But be careful only remove ones that have no initial values or have values that are pure expressions,
// otherwise there may be side effects.
let mut removed = false;
while let Some(expr) = result.pop() {
match expr {
Stmt::Let(_, None, _) => removed = true,
Stmt::Let(_, Some(val_expr), _) if val_expr.is_pure() => removed = true,
_ => {
result.push(expr);
break;
}
}
}
if preserve_result {
if removed {
result.push(Stmt::Noop(pos))
}
result = result
.into_iter()
.rev()
.enumerate()
.map(|(i, s)| optimize_stmt(s, changed, i == 0)) // Optimize all other statements again
.rev()
.collect();
}
*changed = *changed || original_len != result.len();
match result[..] {
[] => {
// No statements in block - change to No-op
[] => {
*changed = true;
Stmt::Noop(pos)
}
[Stmt::Let(_, None, _)] => {
// Only one empty variable declaration - change to No-op
*changed = true;
Stmt::Noop(pos)
}
[Stmt::Let(_, Some(_), _)] => {
// Only one let statement, but cannot promote
// (otherwise the variable gets declared in the scope above)
// and still need to run just in case there are side effects
Stmt::Block(result, pos)
}
[_] => {
// Only one statement - promote
[_] => {
*changed = true;
result.remove(0)
}
@ -103,26 +129,14 @@ fn optimize_stmt(stmt: Stmt, changed: &mut bool) -> Stmt {
is_return,
pos,
),
stmt @ Stmt::ReturnWithVal(None, _, _) => stmt,
stmt @ Stmt::Noop(_) | stmt @ Stmt::Break(_) => stmt,
stmt => stmt,
}
}
fn optimize_expr(expr: Expr, changed: &mut bool) -> Expr {
match expr {
Expr::IntegerConstant(_, _)
| Expr::Identifier(_, _)
| Expr::CharConstant(_, _)
| Expr::StringConstant(_, _)
| Expr::True(_)
| Expr::False(_)
| Expr::Unit(_) => expr,
#[cfg(not(feature = "no_float"))]
Expr::FloatConstant(_, _) => expr,
Expr::Stmt(stmt, pos) => match optimize_stmt(*stmt, changed) {
Expr::Stmt(stmt, pos) => match optimize_stmt(*stmt, changed, true) {
Stmt::Noop(_) => {
*changed = true;
Expr::Unit(pos)
@ -145,11 +159,10 @@ fn optimize_expr(expr: Expr, changed: &mut bool) -> Expr {
#[cfg(not(feature = "no_index"))]
Expr::Index(lhs, rhs, pos) => match (*lhs, *rhs) {
(Expr::Array(mut items, _), Expr::IntegerConstant(i, _))
if i >= 0
&& (i as usize) < items.len()
&& !items.iter().any(|x| x.is_constant() || x.is_identifier()) =>
if i >= 0 && (i as usize) < items.len() && items.iter().all(|x| x.is_pure()) =>
{
// Array where everything is a constant or identifier - promote the item
// Array where everything is a pure - promote the indexed item.
// All other items can be thrown away.
*changed = true;
items.remove(i as usize)
}
@ -215,6 +228,10 @@ fn optimize_expr(expr: Expr, changed: &mut bool) -> Expr {
Box::new(optimize_expr(rhs, changed)),
),
},
// Expr::FunctionCall(id, args, def_value, pos) if id == KEYWORD_DUMP_AST => {
// Expr::FunctionCall(id, args, def_value, pos)
// }
Expr::FunctionCall(id, args, def_value, pos) => {
let original_len = args.len();
@ -227,17 +244,29 @@ fn optimize_expr(expr: Expr, changed: &mut bool) -> Expr {
Expr::FunctionCall(id, args, def_value, pos)
}
expr => expr,
}
}
pub(crate) fn optimize(mut statements: Vec<Stmt>) -> Vec<Stmt> {
pub(crate) fn optimize(statements: Vec<Stmt>) -> Vec<Stmt> {
let mut result = statements;
loop {
let mut changed = false;
statements = statements
result = result
.into_iter()
.map(|stmt| optimize_stmt(stmt, &mut changed))
.filter(Stmt::is_op)
.rev() // Scan in reverse
.enumerate()
.map(|(i, stmt)| {
// Keep all variable declarations at this level
let keep = stmt.is_var();
// Always keep the last return value
optimize_stmt(stmt, &mut changed, keep || i == 0)
})
.rev()
.collect();
if !changed {
@ -245,5 +274,14 @@ pub(crate) fn optimize(mut statements: Vec<Stmt>) -> Vec<Stmt> {
}
}
statements
// Eliminate No-op's but always keep the last statement
let last_stmt = result.pop();
result.retain(Stmt::is_op); // Remove all No-op's
if let Some(stmt) = last_stmt {
result.push(stmt); // Add back the last statement
}
result
}