rhai/src/optimize.rs
2020-09-26 16:27:38 +08:00

833 lines
29 KiB
Rust

//! Module implementing the AST optimizer.
use crate::any::Dynamic;
use crate::calc_fn_hash;
use crate::engine::{
Engine, KEYWORD_DEBUG, KEYWORD_EVAL, KEYWORD_FN_PTR, KEYWORD_PRINT, KEYWORD_TYPE_OF,
};
use crate::fn_native::FnPtr;
use crate::module::Module;
use crate::parser::{map_dynamic_to_expr, Expr, ScriptFnDef, Stmt, AST};
use crate::scope::{Entry as ScopeEntry, EntryType as ScopeEntryType, Scope};
use crate::utils::StaticVec;
#[cfg(not(feature = "no_function"))]
use crate::parser::ReturnType;
#[cfg(feature = "internals")]
use crate::parser::CustomExpr;
use crate::stdlib::{
boxed::Box,
convert::TryFrom,
iter::empty,
string::{String, ToString},
vec,
vec::Vec,
};
/// Level of optimization performed.
///
/// Not available under the `no_optimize` feature.
#[derive(Debug, Eq, PartialEq, Hash, Clone, Copy)]
pub enum OptimizationLevel {
/// No optimization performed.
None,
/// Only perform simple optimizations without evaluating functions.
Simple,
/// Full optimizations performed, including evaluating functions.
/// Take care that this may cause side effects as it essentially assumes that all functions are pure.
Full,
}
impl OptimizationLevel {
/// Is the `OptimizationLevel` None.
pub fn is_none(self) -> bool {
self == Self::None
}
/// Is the `OptimizationLevel` Simple.
#[cfg(not(feature = "no_optimize"))]
pub fn is_simple(self) -> bool {
self == Self::Simple
}
/// Is the `OptimizationLevel` Full.
#[cfg(not(feature = "no_optimize"))]
pub fn is_full(self) -> bool {
self == Self::Full
}
}
/// Mutable state throughout an optimization pass.
struct State<'a> {
/// Has the AST been changed during this pass?
changed: bool,
/// Collection of constants to use for eager function evaluations.
constants: Vec<(String, Expr)>,
/// An `Engine` instance for eager function evaluation.
engine: &'a Engine,
/// Library of script-defined functions.
lib: &'a Module,
/// Optimization level.
optimization_level: OptimizationLevel,
}
impl<'a> State<'a> {
/// Create a new State.
pub fn new(engine: &'a Engine, lib: &'a Module, level: OptimizationLevel) -> Self {
Self {
changed: false,
constants: vec![],
engine,
lib,
optimization_level: level,
}
}
/// Reset the state from dirty to clean.
pub fn reset(&mut self) {
self.changed = false;
}
/// Set the AST state to be dirty (i.e. changed).
pub fn set_dirty(&mut self) {
self.changed = true;
}
/// Is the AST dirty (i.e. changed)?
pub fn is_dirty(&self) -> bool {
self.changed
}
/// Does a constant exist?
pub fn contains_constant(&self, name: &str) -> bool {
self.constants.iter().any(|(n, _)| n == name)
}
/// Prune the list of constants back to a specified size.
pub fn restore_constants(&mut self, len: usize) {
self.constants.truncate(len)
}
/// Add a new constant to the list.
pub fn push_constant(&mut self, name: &str, value: Expr) {
self.constants.push((name.into(), value))
}
/// Look up a constant from the list.
pub fn find_constant(&self, name: &str) -> Option<&Expr> {
for (n, expr) in self.constants.iter().rev() {
if n == name {
return Some(expr);
}
}
None
}
}
/// Call a registered function
fn call_fn_with_constant_arguments(
state: &State,
fn_name: &str,
arg_values: &mut [Dynamic],
) -> Option<Dynamic> {
// Search built-in's and external functions
let hash_fn = calc_fn_hash(
empty(),
fn_name,
arg_values.len(),
arg_values.iter().map(|a| a.type_id()),
);
state
.engine
.call_native_fn(
&mut Default::default(),
state.lib,
fn_name,
hash_fn,
arg_values.iter_mut().collect::<StaticVec<_>>().as_mut(),
false,
true,
&None,
)
.ok()
.map(|(v, _)| v)
}
/// Optimize a statement.
fn optimize_stmt(stmt: Stmt, state: &mut State, preserve_result: bool) -> Stmt {
match stmt {
// if expr { Noop }
Stmt::IfThenElse(x) if matches!(x.1, Stmt::Noop(_)) && x.2.is_none() => {
state.set_dirty();
let pos = x.0.position();
let expr = optimize_expr(x.0, state);
if preserve_result {
// -> { expr, Noop }
let mut statements = StaticVec::new();
statements.push(Stmt::Expr(Box::new(expr)));
statements.push(x.1);
Stmt::Block(Box::new((statements, pos)))
} else {
// -> expr
Stmt::Expr(Box::new(expr))
}
}
// if expr { if_block }
Stmt::IfThenElse(x) if x.2.is_none() => match x.0 {
// if false { if_block } -> Noop
Expr::False(pos) => {
state.set_dirty();
Stmt::Noop(pos)
}
// if true { if_block } -> if_block
Expr::True(_) => optimize_stmt(x.1, state, true),
// if expr { if_block }
expr => Stmt::IfThenElse(Box::new((
optimize_expr(expr, state),
optimize_stmt(x.1, state, true),
None,
x.3,
))),
},
// if expr { if_block } else { else_block }
Stmt::IfThenElse(x) if x.2.is_some() => match x.0 {
// if false { if_block } else { else_block } -> else_block
Expr::False(_) => optimize_stmt(x.2.unwrap(), state, true),
// if true { if_block } else { else_block } -> if_block
Expr::True(_) => optimize_stmt(x.1, state, true),
// if expr { if_block } else { else_block }
expr => Stmt::IfThenElse(Box::new((
optimize_expr(expr, state),
optimize_stmt(x.1, state, true),
match optimize_stmt(x.2.unwrap(), state, true) {
Stmt::Noop(_) => None, // Noop -> no else block
stmt => Some(stmt),
},
x.3,
))),
},
// while expr { block }
Stmt::While(x) => match x.0 {
// while false { block } -> Noop
Expr::False(pos) => {
state.set_dirty();
Stmt::Noop(pos)
}
// while true { block } -> loop { block }
Expr::True(_) => Stmt::Loop(Box::new((optimize_stmt(x.1, state, false), x.2))),
// while expr { block }
expr => match optimize_stmt(x.1, state, false) {
// while expr { break; } -> { expr; }
Stmt::Break(pos) => {
// Only a single break statement - turn into running the guard expression once
state.set_dirty();
let mut statements = StaticVec::new();
statements.push(Stmt::Expr(Box::new(optimize_expr(expr, state))));
if preserve_result {
statements.push(Stmt::Noop(pos))
}
Stmt::Block(Box::new((statements, pos)))
}
// while expr { block }
stmt => Stmt::While(Box::new((optimize_expr(expr, state), stmt, x.2))),
},
},
// loop { block }
Stmt::Loop(x) => match optimize_stmt(x.0, state, false) {
// loop { break; } -> Noop
Stmt::Break(pos) => {
// Only a single break statement
state.set_dirty();
Stmt::Noop(pos)
}
// loop { block }
stmt => Stmt::Loop(Box::new((stmt, x.1))),
},
// for id in expr { block }
Stmt::For(x) => Stmt::For(Box::new((
x.0,
optimize_expr(x.1, state),
optimize_stmt(x.2, state, false),
x.3,
))),
// let id = expr;
Stmt::Let(x) if x.1.is_some() => Stmt::Let(Box::new((
x.0,
Some(optimize_expr(x.1.unwrap(), state)),
x.2,
))),
// let id;
stmt @ Stmt::Let(_) => stmt,
// import expr as id;
#[cfg(not(feature = "no_module"))]
Stmt::Import(x) => Stmt::Import(Box::new((optimize_expr(x.0, state), x.1, x.2))),
// { block }
Stmt::Block(x) => {
let orig_len = x.0.len(); // Original number of statements in the block, for change detection
let orig_constants_len = state.constants.len(); // Original number of constants in the state, for restore later
let pos = x.1;
// Optimize each statement in the block
let mut result: Vec<_> =
x.0.into_iter()
.map(|stmt| match stmt {
// Add constant into the state
Stmt::Const(v) => {
let ((name, pos), expr, _) = *v;
state.push_constant(&name, expr);
state.set_dirty();
Stmt::Noop(pos) // No need to keep constants
}
// Optimize the statement
_ => optimize_stmt(stmt, state, preserve_result),
})
.collect();
// 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| !stmt.is_pure());
if let Some(stmt) = last_stmt {
result.push(stmt);
}
// Remove all let/import 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(x) if x.1.is_none() => removed = true,
Stmt::Let(x) if x.1.is_some() => removed = x.1.unwrap().is_pure(),
#[cfg(not(feature = "no_module"))]
Stmt::Import(x) => removed = x.0.is_pure(),
_ => {
result.push(expr);
break;
}
}
}
if preserve_result {
if removed {
result.push(Stmt::Noop(pos))
}
// Optimize all the statements again
result = result
.into_iter()
.rev()
.enumerate()
.map(|(i, s)| optimize_stmt(s, state, i == 0))
.rev()
.collect();
}
// Remove everything following the the first return/throw
let mut dead_code = false;
result.retain(|stmt| {
if dead_code {
return false;
}
match stmt {
Stmt::ReturnWithVal(_) | Stmt::Break(_) => {
dead_code = true;
}
_ => (),
}
true
});
// Change detection
if orig_len != result.len() {
state.set_dirty();
}
// Pop the stack and remove all the local constants
state.restore_constants(orig_constants_len);
match result[..] {
// No statements in block - change to No-op
[] => {
state.set_dirty();
Stmt::Noop(pos)
}
// Only one let statement - leave it alone
[Stmt::Let(_)] => Stmt::Block(Box::new((result.into(), pos))),
// Only one import statement - leave it alone
#[cfg(not(feature = "no_module"))]
[Stmt::Import(_)] => Stmt::Block(Box::new((result.into(), pos))),
// Only one statement - promote
[_] => {
state.set_dirty();
result.remove(0)
}
_ => Stmt::Block(Box::new((result.into(), pos))),
}
}
// expr;
Stmt::Expr(expr) => Stmt::Expr(Box::new(optimize_expr(*expr, state))),
// return expr;
Stmt::ReturnWithVal(x) if x.1.is_some() => Stmt::ReturnWithVal(Box::new((
x.0,
Some(optimize_expr(x.1.unwrap(), state)),
x.2,
))),
// All other statements - skip
stmt => stmt,
}
}
/// Optimize an expression.
fn optimize_expr(expr: Expr, state: &mut State) -> Expr {
// These keywords are handled specially
const DONT_EVAL_KEYWORDS: [&str; 3] = [KEYWORD_PRINT, KEYWORD_DEBUG, KEYWORD_EVAL];
match expr {
// expr - do not promote because there is a reason it is wrapped in an `Expr::Expr`
Expr::Expr(x) => Expr::Expr(Box::new(optimize_expr(*x, state))),
// ( stmt )
Expr::Stmt(x) => match optimize_stmt(x.0, state, true) {
// ( Noop ) -> ()
Stmt::Noop(_) => {
state.set_dirty();
Expr::Unit(x.1)
}
// ( expr ) -> expr
Stmt::Expr(expr) => {
state.set_dirty();
*expr
}
// ( stmt )
stmt => Expr::Stmt(Box::new((stmt, x.1))),
},
// id op= expr
Expr::Assignment(x) => Expr::Assignment(Box::new((x.0, x.1, optimize_expr(x.2, state), x.3))),
// lhs.rhs
#[cfg(not(feature = "no_object"))]
Expr::Dot(x) => match (x.0, x.1) {
// map.string
(Expr::Map(m), Expr::Property(p)) if m.0.iter().all(|(_, x)| x.is_pure()) => {
let ((prop, _, _), _) = p.as_ref();
// Map literal where everything is pure - promote the indexed item.
// All other items can be thrown away.
state.set_dirty();
let pos = m.1;
m.0.into_iter().find(|((name, _), _)| name == prop)
.map(|(_, mut expr)| { expr.set_position(pos); expr })
.unwrap_or_else(|| Expr::Unit(pos))
}
// lhs.rhs
(lhs, rhs) => Expr::Dot(Box::new((optimize_expr(lhs, state), optimize_expr(rhs, state), x.2)))
}
// lhs[rhs]
#[cfg(not(feature = "no_index"))]
Expr::Index(x) => match (x.0, x.1) {
// array[int]
(Expr::Array(mut a), Expr::IntegerConstant(i))
if i.0 >= 0 && (i.0 as usize) < a.0.len() && a.0.iter().all(Expr::is_pure) =>
{
// Array literal where everything is pure - promote the indexed item.
// All other items can be thrown away.
state.set_dirty();
let mut expr = a.0.remove(i.0 as usize);
expr.set_position(a.1);
expr
}
// map[string]
(Expr::Map(m), Expr::StringConstant(s)) if m.0.iter().all(|(_, x)| x.is_pure()) => {
// Map literal where everything is pure - promote the indexed item.
// All other items can be thrown away.
state.set_dirty();
let pos = m.1;
m.0.into_iter().find(|((name, _), _)| *name == s.0)
.map(|(_, mut expr)| { expr.set_position(pos); expr })
.unwrap_or_else(|| Expr::Unit(pos))
}
// string[int]
(Expr::StringConstant(s), Expr::IntegerConstant(i)) if i.0 >= 0 && (i.0 as usize) < s.0.chars().count() => {
// String literal indexing - get the character
state.set_dirty();
Expr::CharConstant(Box::new((s.0.chars().nth(i.0 as usize).unwrap(), s.1)))
}
// lhs[rhs]
(lhs, rhs) => Expr::Index(Box::new((optimize_expr(lhs, state), optimize_expr(rhs, state), x.2))),
},
// [ items .. ]
#[cfg(not(feature = "no_index"))]
Expr::Array(a) => Expr::Array(Box::new((a.0
.into_iter().map(|expr| optimize_expr(expr, state))
.collect(), a.1))),
// [ items .. ]
#[cfg(not(feature = "no_object"))]
Expr::Map(m) => Expr::Map(Box::new((m.0
.into_iter().map(|((key, pos), expr)| ((key, pos), optimize_expr(expr, state)))
.collect(), m.1))),
// lhs in rhs
Expr::In(x) => match (x.0, x.1) {
// "xxx" in "xxxxx"
(Expr::StringConstant(a), Expr::StringConstant(b)) => {
state.set_dirty();
if b.0.contains(a.0.as_str()) { Expr::True(a.1) } else { Expr::False(a.1) }
}
// 'x' in "xxxxx"
(Expr::CharConstant(a), Expr::StringConstant(b)) => {
state.set_dirty();
if b.0.contains(a.0) { Expr::True(a.1) } else { Expr::False(a.1) }
}
// "xxx" in #{...}
(Expr::StringConstant(a), Expr::Map(b)) => {
state.set_dirty();
if b.0.iter().find(|((name, _), _)| *name == a.0).is_some() {
Expr::True(a.1)
} else {
Expr::False(a.1)
}
}
// 'x' in #{...}
(Expr::CharConstant(a), Expr::Map(b)) => {
state.set_dirty();
let ch = a.0.to_string();
if b.0.iter().find(|((name, _), _)| name == &ch).is_some() {
Expr::True(a.1)
} else {
Expr::False(a.1)
}
}
// lhs in rhs
(lhs, rhs) => Expr::In(Box::new((optimize_expr(lhs, state), optimize_expr(rhs, state), x.2))),
},
// lhs && rhs
Expr::And(x) => match (x.0, x.1) {
// true && rhs -> rhs
(Expr::True(_), rhs) => {
state.set_dirty();
rhs
}
// false && rhs -> false
(Expr::False(pos), _) => {
state.set_dirty();
Expr::False(pos)
}
// lhs && true -> lhs
(lhs, Expr::True(_)) => {
state.set_dirty();
optimize_expr(lhs, state)
}
// lhs && rhs
(lhs, rhs) => Expr::And(Box::new((optimize_expr(lhs, state), optimize_expr(rhs, state), x.2))),
},
// lhs || rhs
Expr::Or(x) => match (x.0, x.1) {
// false || rhs -> rhs
(Expr::False(_), rhs) => {
state.set_dirty();
rhs
}
// true || rhs -> true
(Expr::True(pos), _) => {
state.set_dirty();
Expr::True(pos)
}
// lhs || false
(lhs, Expr::False(_)) => {
state.set_dirty();
optimize_expr(lhs, state)
}
// lhs || rhs
(lhs, rhs) => Expr::Or(Box::new((optimize_expr(lhs, state), optimize_expr(rhs, state), x.2))),
},
// Do not call some special keywords
Expr::FnCall(mut x) if DONT_EVAL_KEYWORDS.contains(&(x.0).0.as_ref())=> {
x.3 = x.3.into_iter().map(|a| optimize_expr(a, state)).collect();
Expr::FnCall(x)
}
// Fn("...")
Expr::FnCall(x)
if x.1.is_none()
&& (x.0).0 == KEYWORD_FN_PTR
&& x.3.len() == 1
&& matches!(x.3[0], Expr::StringConstant(_))
=> {
if let Expr::StringConstant(s) = &x.3[0] {
if let Ok(fn_ptr) = FnPtr::try_from(s.0.as_str()) {
Expr::FnPointer(Box::new((fn_ptr.take_data().0, s.1)))
} else {
Expr::FnCall(x)
}
} else {
unreachable!()
}
}
// Eagerly call functions
Expr::FnCall(mut x)
if x.1.is_none() // Non-qualified
&& state.optimization_level == OptimizationLevel::Full // full optimizations
&& x.3.iter().all(|expr| expr.is_constant()) // all arguments are constants
=> {
let ((name, _, _, pos), _, _, args, def_value) = x.as_mut();
// First search in functions lib (can override built-in)
// Cater for both normal function call style and method call style (one additional arguments)
let has_script_fn = cfg!(not(feature = "no_function")) && state.lib.iter_fn().find(|(_, _, _, _,f)| {
if !f.is_script() { return false; }
let fn_def = f.get_fn_def();
fn_def.name == name && (args.len()..=args.len() + 1).contains(&fn_def.params.len())
}).is_some();
if has_script_fn {
// A script-defined function overrides the built-in function - do not make the call
x.3 = x.3.into_iter().map(|a| optimize_expr(a, state)).collect();
return Expr::FnCall(x);
}
let mut arg_values: StaticVec<_> = args.iter().map(Expr::get_constant_value).collect();
// Save the typename of the first argument if it is `type_of()`
// This is to avoid `call_args` being passed into the closure
let arg_for_type_of = if name == KEYWORD_TYPE_OF && arg_values.len() == 1 {
state.engine.map_type_name(arg_values[0].type_name())
} else {
""
};
call_fn_with_constant_arguments(&state, name, arg_values.as_mut())
.or_else(|| {
if !arg_for_type_of.is_empty() {
// Handle `type_of()`
Some(arg_for_type_of.to_string().into())
} else {
// Otherwise use the default value, if any
def_value.map(|v| v.into())
}
})
.and_then(|result| map_dynamic_to_expr(result, *pos))
.map(|expr| {
state.set_dirty();
expr
})
.unwrap_or_else(|| {
// Optimize function call arguments
x.3 = x.3.into_iter().map(|a| optimize_expr(a, state)).collect();
Expr::FnCall(x)
})
}
// id(args ..) -> optimize function call arguments
Expr::FnCall(mut x) => {
x.3 = x.3.into_iter().map(|a| optimize_expr(a, state)).collect();
Expr::FnCall(x)
}
// constant-name
Expr::Variable(x) if x.1.is_none() && state.contains_constant(&(x.0).0) => {
let (name, pos) = x.0;
state.set_dirty();
// Replace constant with value
let mut expr = state.find_constant(&name).unwrap().clone();
expr.set_position(pos);
expr
}
// Custom syntax
#[cfg(feature = "internals")]
Expr::Custom(x) => Expr::Custom(Box::new((
CustomExpr(
(x.0).0.into_iter().map(|expr| optimize_expr(expr, state)).collect(),
(x.0).1),
x.1
))),
// All other expressions - skip
expr => expr,
}
}
fn optimize(
statements: Vec<Stmt>,
engine: &Engine,
scope: &Scope,
lib: &Module,
level: OptimizationLevel,
) -> Vec<Stmt> {
// If optimization level is None then skip optimizing
if level == OptimizationLevel::None {
return statements;
}
// Set up the state
let mut state = State::new(engine, lib, level);
// Add constants from the scope into the state
scope
.to_iter()
.filter(|ScopeEntry { typ, expr, .. }| {
// Get all the constants with definite constant expressions
*typ == ScopeEntryType::Constant
&& expr.as_ref().map(|v| v.is_constant()).unwrap_or(false)
})
.for_each(|ScopeEntry { name, expr, .. }| {
state.push_constant(name.as_ref(), expr.as_ref().unwrap().as_ref().clone())
});
let orig_constants_len = state.constants.len();
let mut result = statements;
// Optimization loop
loop {
state.reset();
state.restore_constants(orig_constants_len);
let num_statements = result.len();
result = result
.into_iter()
.enumerate()
.map(|(i, stmt)| {
match &stmt {
Stmt::Const(v) => {
// Load constants
let ((name, _), expr, _) = v.as_ref();
state.push_constant(&name, expr.clone());
stmt // Keep it in the global scope
}
_ => {
// Keep all variable declarations at this level
// and always keep the last return value
let keep = match stmt {
Stmt::Let(_) => true,
#[cfg(not(feature = "no_module"))]
Stmt::Import(_) => true,
_ => i == num_statements - 1,
};
optimize_stmt(stmt, &mut state, keep)
}
}
})
.collect();
if !state.is_dirty() {
break;
}
}
// Eliminate code that is pure but always keep the last statement
let last_stmt = result.pop();
// Remove all pure statements at global level
result.retain(|stmt| !stmt.is_pure());
// Add back the last statement unless it is a lone No-op
if let Some(stmt) = last_stmt {
if !result.is_empty() || !matches!(stmt, Stmt::Noop(_)) {
result.push(stmt);
}
}
result
}
/// Optimize an AST.
pub fn optimize_into_ast(
engine: &Engine,
scope: &Scope,
statements: Vec<Stmt>,
_functions: Vec<ScriptFnDef>,
level: OptimizationLevel,
) -> AST {
let level = if cfg!(feature = "no_optimize") {
OptimizationLevel::None
} else {
level
};
#[cfg(not(feature = "no_function"))]
let lib = {
let mut module = Module::new();
if !level.is_none() {
// We only need the script library's signatures for optimization purposes
let mut lib2 = Module::new();
_functions
.iter()
.map(|fn_def| {
ScriptFnDef {
name: fn_def.name.clone(),
access: fn_def.access,
body: Default::default(),
params: fn_def.params.clone(),
#[cfg(not(feature = "no_closure"))]
externals: fn_def.externals.clone(),
pos: fn_def.pos,
}
.into()
})
.for_each(|fn_def| {
lib2.set_script_fn(fn_def);
});
_functions
.into_iter()
.map(|mut fn_def| {
let pos = fn_def.body.position();
// Optimize the function body
let mut body = optimize(vec![fn_def.body], engine, &Scope::new(), &lib2, level);
// {} -> Noop
fn_def.body = match body.pop().unwrap_or_else(|| Stmt::Noop(pos)) {
// { return val; } -> val
Stmt::ReturnWithVal(x)
if x.1.is_some() && (x.0).0 == ReturnType::Return =>
{
Stmt::Expr(Box::new(x.1.unwrap()))
}
// { return; } -> ()
Stmt::ReturnWithVal(x)
if x.1.is_none() && (x.0).0 == ReturnType::Return =>
{
Stmt::Expr(Box::new(Expr::Unit((x.0).1)))
}
// All others
stmt => stmt,
};
fn_def.into()
})
.for_each(|fn_def| {
module.set_script_fn(fn_def);
});
} else {
_functions.into_iter().for_each(|fn_def| {
module.set_script_fn(fn_def);
});
}
module
};
#[cfg(feature = "no_function")]
let lib = Default::default();
AST::new(
match level {
OptimizationLevel::None => statements,
OptimizationLevel::Simple | OptimizationLevel::Full => {
optimize(statements, engine, &scope, &lib, level)
}
},
lib,
)
}