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Do not propagate constants if shadowed.

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This commit is contained in:
Stephen Chung 2020-12-08 22:20:29 +08:00
parent aff207d4f4
commit 8e8069f819
3 changed files with 64 additions and 43 deletions
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9
RELEASES.md
View File

@ -1,6 +1,15 @@
Rhai Release Notes
==================
Version 0.19.8
==============
Bug fixes
---------
* Constants are no longer propagated by the optimizer if shadowed by a non-constant variable.
Version 0.19.7
==============

82
src/optimize.rs
View File

@ -1,6 +1,7 @@
//! Module implementing the [`AST`] optimizer.
use crate::ast::{Expr, ScriptFnDef, Stmt};
use crate::dynamic::AccessType;
use crate::engine::{KEYWORD_DEBUG, KEYWORD_EVAL, KEYWORD_PRINT, KEYWORD_TYPE_OF};
use crate::fn_call::run_builtin_binary_op;
use crate::parser::map_dynamic_to_expr;
@ -58,7 +59,7 @@ 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)>,
variables: Vec<(String, AccessType, Expr)>,
/// An [`Engine`] instance for eager function evaluation.
engine: &'a Engine,
/// [Module] containing script-defined functions.
@ -73,7 +74,7 @@ impl<'a> State<'a> {
pub fn new(engine: &'a Engine, lib: &'a [&'a Module], level: OptimizationLevel) -> Self {
Self {
changed: false,
constants: vec![],
variables: vec![],
engine,
lib,
optimization_level: level,
@ -94,27 +95,26 @@ impl<'a> State<'a> {
pub fn is_dirty(&self) -> bool {
self.changed
}
/// Does a constant exist?
#[inline(always)]
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.
#[inline(always)]
pub fn restore_constants(&mut self, len: usize) {
self.constants.truncate(len)
pub fn restore_var(&mut self, len: usize) {
self.variables.truncate(len)
}
/// Add a new constant to the list.
#[inline(always)]
pub fn push_constant(&mut self, name: &str, value: Expr) {
self.constants.push((name.into(), value))
pub fn push_var(&mut self, name: &str, access: AccessType, value: Expr) {
self.variables.push((name.into(), access, value))
}
/// Look up a constant from the list.
#[inline]
pub fn find_constant(&self, name: &str) -> Option<&Expr> {
for (n, expr) in self.constants.iter().rev() {
for (n, access, expr) in self.variables.iter().rev() {
if n == name {
return Some(expr);
return if access.is_constant() {
Some(expr)
} else {
None
};
}
}
@ -157,20 +157,20 @@ fn optimize_stmt_block(
count_promote_as_dirty: bool,
) -> Stmt {
let orig_len = statements.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 orig_constants_len = state.variables.len(); // Original number of constants in the state, for restore later
// Optimize each statement in the block
statements.iter_mut().for_each(|stmt| match stmt {
// Add constant literals into the state
Stmt::Const(var_def, Some(expr), _, pos) if expr.is_constant() => {
state.set_dirty();
state.push_constant(&var_def.name, mem::take(expr));
*stmt = Stmt::Noop(*pos); // No need to keep constants
Stmt::Const(var_def, Some(expr), _, _) if expr.is_constant() => {
state.push_var(&var_def.name, AccessType::Constant, mem::take(expr));
}
Stmt::Const(var_def, None, _, pos) => {
state.set_dirty();
state.push_constant(&var_def.name, Expr::Unit(var_def.pos));
*stmt = Stmt::Noop(*pos); // No need to keep constants
Stmt::Const(var_def, None, _, _) => {
state.push_var(&var_def.name, AccessType::Constant, Expr::Unit(var_def.pos));
}
// Add variables into the state
Stmt::Let(var_def, _, _, _) => {
state.push_var(&var_def.name, AccessType::Normal, Expr::Unit(var_def.pos));
}
// Optimize the statement
_ => optimize_stmt(stmt, state, preserve_result),
@ -196,7 +196,9 @@ fn optimize_stmt_block(
while let Some(expr) = statements.pop() {
match expr {
Stmt::Let(_, expr, _, _) => removed = expr.as_ref().map(Expr::is_pure).unwrap_or(true),
Stmt::Let(_, expr, _, _) | Stmt::Const(_, expr, _, _) => {
removed = expr.as_ref().map(Expr::is_pure).unwrap_or(true)
}
#[cfg(not(feature = "no_module"))]
Stmt::Import(expr, _, _) => removed = expr.is_pure(),
_ => {
@ -241,7 +243,7 @@ fn optimize_stmt_block(
}
// Pop the stack and remove all the local constants
state.restore_constants(orig_constants_len);
state.restore_var(orig_constants_len);
match &statements[..] {
// No statements in block - change to No-op
@ -251,6 +253,8 @@ fn optimize_stmt_block(
}
// Only one let statement - leave it alone
[x] if matches!(x, Stmt::Let(_, _, _, _)) => Stmt::Block(statements, pos),
// Only one const statement - leave it alone
[x] if matches!(x, Stmt::Const(_, _, _, _)) => Stmt::Block(statements, pos),
// Only one import statement - leave it alone
#[cfg(not(feature = "no_module"))]
[x] if matches!(x, Stmt::Import(_, _, _)) => Stmt::Block(statements, pos),
@ -708,7 +712,7 @@ fn optimize_expr(expr: &mut Expr, state: &mut State) {
Expr::FnCall(x, _) => x.args.iter_mut().for_each(|a| optimize_expr(a, state)),
// constant-name
Expr::Variable(x) if x.1.is_none() && state.contains_constant(&x.3.name) => {
Expr::Variable(x) if x.1.is_none() && state.find_constant(&x.3.name).is_some() => {
state.set_dirty();
// Replace constant with value
@ -742,22 +746,23 @@ fn optimize_top_level(
// Set up the state
let mut state = State::new(engine, lib, level);
// Add constants from the scope that can be made into a literal into the state
scope
.iter()
.filter(|(_, typ, _)| *typ)
.for_each(|(name, _, value)| {
if let Some(val) = map_dynamic_to_expr(value, Position::NONE) {
state.push_constant(name, val);
// Add constants and variables from the scope
scope.iter().for_each(|(name, constant, value)| {
if !constant {
state.push_var(name, AccessType::Normal, Expr::Unit(Position::NONE));
} else if let Some(val) = map_dynamic_to_expr(value, Position::NONE) {
state.push_var(name, AccessType::Constant, val);
} else {
state.push_var(name, AccessType::Constant, Expr::Unit(Position::NONE));
}
});
let orig_constants_len = state.constants.len();
let orig_constants_len = state.variables.len();
// Optimization loop
loop {
state.reset();
state.restore_constants(orig_constants_len);
state.restore_var(orig_constants_len);
let num_statements = statements.len();
@ -769,7 +774,7 @@ fn optimize_top_level(
optimize_expr(value_expr, &mut state);
if value_expr.is_constant() {
state.push_constant(&var_def.name, value_expr.clone());
state.push_var(&var_def.name, AccessType::Constant, value_expr.clone());
}
// Keep it in the global scope
@ -779,13 +784,16 @@ fn optimize_top_level(
}
}
Stmt::Const(var_def, None, _, _) => {
state.push_constant(&var_def.name, Expr::Unit(var_def.pos));
state.push_var(&var_def.name, AccessType::Constant, Expr::Unit(var_def.pos));
}
Stmt::Let(var_def, _, _, _) => {
state.push_var(&var_def.name, AccessType::Normal, Expr::Unit(var_def.pos));
}
_ => {
// Keep all variable declarations at this level
// and always keep the last return value
let keep = match stmt {
Stmt::Let(_, _, _, _) => true,
Stmt::Let(_, _, _, _) | Stmt::Const(_, _, _, _) => true,
#[cfg(not(feature = "no_module"))]
Stmt::Import(_, _, _) => true,
_ => i == num_statements - 1,

12
tests/optimizer.rs
View File

@ -53,15 +53,19 @@ fn test_optimizer_parse() -> Result<(), Box<EvalAltResult>> {
let mut engine = Engine::new();
engine.set_optimization_level(OptimizationLevel::Simple);
let ast = engine.compile("{ const DECISION = false; if DECISION { 42 } }")?;
let ast = engine.compile("{ const DECISION = false; if DECISION { 42 } else { 123 } }")?;
assert!(format!("{:?}", ast).starts_with("AST([], Module("));
engine.set_optimization_level(OptimizationLevel::Full);
assert!(format!("{:?}", ast).starts_with(r#"AST([Block([Const(Ident { name: "DECISION", pos: 1:9 }, Some(Unit(0:0)), false, 1:3), Expr(IntegerConstant(123, 1:53))], 1:1)]"#));
let ast = engine.compile("if 1 == 2 { 42 }")?;
assert!(format!("{:?}", ast).starts_with("AST([], Module("));
engine.set_optimization_level(OptimizationLevel::Full);
let ast = engine.compile("abs(-42)")?;
assert!(format!("{:?}", ast).starts_with(r"AST([Expr(IntegerConstant(42, 1:1))]"));
Ok(())
}