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Reduce lifted out variants.

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This commit is contained in:
Stephen Chung 2023-03-16 19:00:59 +08:00
parent c7d40945ee
commit a3324ceb3d
3 changed files with 72 additions and 85 deletions
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7
src/engine.rs
View File

@ -369,8 +369,15 @@ impl Engine {
}
/// Imitation of std::hints::black_box which requires nightly.
#[cfg(not(target_family = "wasm"))]
#[inline(never)]
pub(crate) fn black_box() -> usize {
unsafe { core::ptr::read_volatile(&0_usize as *const usize) }
}
/// Imitation of std::hints::black_box which requires nightly.
#[cfg(target_family = "wasm")]
#[inline(always)]
pub(crate) fn black_box() -> usize {
0
}
}

51
src/eval/expr.rs
View File

@ -254,8 +254,6 @@ impl Engine {
}
// Then variable access.
// We shouldn't do this for too many variants because, soon or later, the added comparisons
// will cost more than the mis-predicted `match` branch.
if let Expr::Variable(x, index, var_pos) = expr {
return if index.is_none() && x.0.is_none() && x.3 == KEYWORD_THIS {
this_ptr
@ -267,41 +265,27 @@ impl Engine {
};
}
// Stop merging branches here!
Self::black_box();
// Constants
// Then integer constants.
if let Expr::IntegerConstant(x, ..) = expr {
return Ok((*x).into());
}
if let Expr::StringConstant(x, ..) = expr {
return Ok(x.clone().into());
}
if let Expr::BoolConstant(x, ..) = expr {
return Ok((*x).into());
}
// Stop merging branches here!
Self::black_box();
#[cfg(not(feature = "no_float"))]
if let Expr::FloatConstant(x, ..) = expr {
return Ok((*x).into());
}
if let Expr::CharConstant(x, ..) = expr {
return Ok((*x).into());
}
if let Expr::Unit(..) = expr {
return Ok(Dynamic::UNIT);
}
if let Expr::DynamicConstant(x, ..) = expr {
return Ok(x.as_ref().clone());
}
// Stop merging branches here!
// We shouldn't lift out too many variants because, soon or later, the added comparisons
// will cost more than the mis-predicted `match` branch.
Self::black_box();
match expr {
// Constants
Expr::IntegerConstant(..) => unreachable!(),
Expr::StringConstant(x, ..) => Ok(x.clone().into()),
Expr::BoolConstant(x, ..) => Ok((*x).into()),
#[cfg(not(feature = "no_float"))]
Expr::FloatConstant(x, ..) => Ok((*x).into()),
Expr::CharConstant(x, ..) => Ok((*x).into()),
Expr::Unit(..) => Ok(Dynamic::UNIT),
Expr::DynamicConstant(x, ..) => Ok(x.as_ref().clone()),
// `... ${...} ...`
Expr::InterpolatedString(x, _) => {
let mut concat = SmartString::new_const();
@ -445,8 +429,13 @@ impl Engine {
.and_then(|r| self.check_data_size(r, expr.start_position()))
}
Expr::Stmt(x) if x.is_empty() => Ok(Dynamic::UNIT),
Expr::Stmt(x) => self.eval_stmt_block(global, caches, scope, this_ptr, x, true),
Expr::Stmt(x) => {
if x.is_empty() {
Ok(Dynamic::UNIT)
} else {
self.eval_stmt_block(global, caches, scope, this_ptr, x, true)
}
}
#[cfg(not(feature = "no_index"))]
Expr::Index(..) => {

59
src/eval/stmt.rs
View File

@ -277,7 +277,6 @@ impl Engine {
// Coded this way for better branch prediction.
// Popular branches are lifted out of the `match` statement into their own branches.
// Hopefully the compiler won't undo all this work!
// Function calls should account for a relatively larger portion of statements.
if let Stmt::FnCall(x, pos) = stmt {
@ -285,8 +284,6 @@ impl Engine {
}
// Then assignments.
// We shouldn't do this for too many variants because, soon or later, the added comparisons
// will cost more than the mis-predicted `match` branch.
if let Stmt::Assignment(x, ..) = stmt {
let (op_info, BinaryExpr { lhs, rhs }) = &**x;
@ -353,22 +350,12 @@ impl Engine {
}
}
// Stop merging branches here!
Self::black_box();
// Block scope
if let Stmt::Block(statements, ..) = stmt {
return if statements.is_empty() {
Ok(Dynamic::UNIT)
} else {
self.eval_stmt_block(global, caches, scope, this_ptr, statements, true)
};
}
// Then variable definitions.
if let Stmt::Var(x, options, pos) = stmt {
if !self.allow_shadowing() && scope.contains(&x.0) {
return Err(ERR::ErrorVariableExists(x.0.to_string(), *pos).into());
}
// Let/const statement
let (var_name, expr, index) = &**x;
@ -451,10 +438,30 @@ impl Engine {
}
// Stop merging branches here!
// We shouldn't lift out too many variants because, soon or later, the added comparisons
// will cost more than the mis-predicted `match` branch.
Self::black_box();
match stmt {
// No-op
Stmt::Noop(..) => Ok(Dynamic::UNIT),
// Expression as statement
Stmt::Expr(expr) => self
.eval_expr(global, caches, scope, this_ptr, expr)
.map(Dynamic::flatten),
// Block scope
Stmt::Block(statements, ..) => {
if statements.is_empty() {
Ok(Dynamic::UNIT)
} else {
self.eval_stmt_block(global, caches, scope, this_ptr, statements, true)
}
}
// If statement
if let Stmt::If(x, ..) = stmt {
Stmt::If(x, ..) => {
let FlowControl {
expr,
body: if_block,
@ -466,7 +473,7 @@ impl Engine {
.as_bool()
.map_err(|typ| self.make_type_mismatch_err::<bool>(typ, expr.position()))?;
return match guard_val {
match guard_val {
true if !if_block.is_empty() => {
self.eval_stmt_block(global, caches, scope, this_ptr, if_block, true)
}
@ -474,25 +481,9 @@ impl Engine {
self.eval_stmt_block(global, caches, scope, this_ptr, else_block, true)
}
_ => Ok(Dynamic::UNIT),
};
}
}
// Expression as statement
if let Stmt::Expr(expr) = stmt {
return self
.eval_expr(global, caches, scope, this_ptr, expr)
.map(Dynamic::flatten);
}
// No-op
if let Stmt::Noop(..) = stmt {
return Ok(Dynamic::UNIT);
}
// Stop merging branches here!
Self::black_box();
match stmt {
// Switch statement
Stmt::Switch(x, ..) => {
let (