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Switch case condition that is constant () no longer optimizes to false.

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This commit is contained in:
Stephen Chung 2022-07-18 23:28:12 +08:00
parent ff6954d9d5
commit 281e94fc62
3 changed files with 105 additions and 106 deletions
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5
CHANGELOG.md
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@ -6,6 +6,11 @@ Version 1.9.0
The minimum Rust version is now `1.60.0` in order to use the `dep:` syntax for dependencies.
Bug fixes
---------
* `switch` cases with conditions that evaluate to constant `()` no longer optimize to `false` (should raise a type error during runtime).
New features
------------

21
src/ast/stmt.rs
View File

@ -153,6 +153,27 @@ impl<B: Into<StmtBlock>> From<(Expr, B)> for ConditionalStmtBlock {
}
}
impl ConditionalStmtBlock {
/// Is this conditional statements block always `true`?
#[inline(always)]
#[must_use]
pub fn is_always_true(&self) -> bool {
match self.condition {
Expr::BoolConstant(true, ..) => true,
_ => false,
}
}
/// Is this conditional statements block always `false`?
#[inline(always)]
#[must_use]
pub fn is_always_false(&self) -> bool {
match self.condition {
Expr::BoolConstant(false, ..) => true,
_ => false,
}
}
}
/// _(internals)_ A type containing a range case for a `switch` statement.
/// Exported under the `internals` feature only.
#[derive(Clone, Hash)]

75
src/optimizer.rs
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@ -547,17 +547,15 @@ fn optimize_stmt(stmt: &mut Stmt, state: &mut OptimizerState, preserve_result: b
let mut b = mem::take(&mut case_blocks[*index]);
cases.clear();
match b.condition {
Expr::BoolConstant(true, ..) => {
if b.is_always_true() {
// Promote the matched case
let statements: StmtBlockContainer = mem::take(&mut b.statements);
let statements =
optimize_stmt_block(statements, state, true, true, false);
*stmt = (statements, b.statements.span()).into();
}
ref mut condition => {
} else {
// switch const { case if condition => stmt, _ => def } => if condition { stmt } else { def }
optimize_expr(condition, state, false);
optimize_expr(&mut b.condition, state, false);
let else_stmt = if let Some(index) = def_case {
let def_case = &mut case_blocks[*index].statements;
@ -572,7 +570,7 @@ fn optimize_stmt(stmt: &mut Stmt, state: &mut OptimizerState, preserve_result: b
*stmt = Stmt::If(
(
mem::take(condition),
mem::take(&mut b.condition),
mem::take(&mut b.statements),
else_stmt,
)
@ -580,7 +578,6 @@ fn optimize_stmt(stmt: &mut Stmt, state: &mut OptimizerState, preserve_result: b
match_expr.start_position(),
);
}
}
state.set_dirty();
return;
@ -589,19 +586,15 @@ fn optimize_stmt(stmt: &mut Stmt, state: &mut OptimizerState, preserve_result: b
for &index in case_blocks_list {
let mut b = mem::take(&mut case_blocks[index]);
match b.condition {
Expr::BoolConstant(true, ..) => {
if b.is_always_true() {
// Promote the matched case
let statements: StmtBlockContainer =
mem::take(&mut b.statements);
let statements: StmtBlockContainer = mem::take(&mut b.statements);
let statements =
optimize_stmt_block(statements, state, true, true, false);
*stmt = (statements, b.statements.span()).into();
state.set_dirty();
return;
}
_ => (),
}
}
}
}
@ -613,26 +606,23 @@ fn optimize_stmt(stmt: &mut Stmt, state: &mut OptimizerState, preserve_result: b
// Only one range or all ranges without conditions
if ranges.len() == 1
|| ranges.iter().all(|r| {
matches!(
case_blocks[r.index()].condition,
Expr::BoolConstant(true, ..)
)
})
|| ranges
.iter()
.all(|r| case_blocks[r.index()].is_always_true())
{
for r in ranges.iter().filter(|r| r.contains(value)) {
let condition = mem::take(&mut case_blocks[r.index()].condition);
let range_block = &mut case_blocks[r.index()];
match condition {
Expr::BoolConstant(true, ..) => {
if range_block.is_always_true() {
// Promote the matched case
let block = &mut case_blocks[r.index()];
let statements = mem::take(&mut *block.statements);
let statements =
optimize_stmt_block(statements, state, true, true, false);
*stmt = (statements, block.statements.span()).into();
}
mut condition => {
} else {
let mut condition = mem::take(&mut range_block.condition);
// switch const { range if condition => stmt, _ => def } => if condition { stmt } else { def }
optimize_expr(&mut condition, state, false);
@ -654,7 +644,6 @@ fn optimize_stmt(stmt: &mut Stmt, state: &mut OptimizerState, preserve_result: b
match_expr.start_position(),
);
}
}
state.set_dirty();
return;
@ -681,14 +670,6 @@ fn optimize_stmt(stmt: &mut Stmt, state: &mut OptimizerState, preserve_result: b
optimize_stmt_block(statements, state, preserve_result, true, false);
optimize_expr(&mut b.condition, state, false);
match b.condition {
Expr::Unit(pos) => {
b.condition = Expr::BoolConstant(true, pos);
state.set_dirty()
}
_ => (),
}
}
return;
}
@ -730,38 +711,29 @@ fn optimize_stmt(stmt: &mut Stmt, state: &mut OptimizerState, preserve_result: b
optimize_expr(&mut b.condition, state, false);
match b.condition {
Expr::Unit(pos) => {
b.condition = Expr::BoolConstant(true, pos);
state.set_dirty();
}
Expr::BoolConstant(false, ..) => {
if b.is_always_false() {
if !b.statements.is_empty() {
b.statements = StmtBlock::NONE;
state.set_dirty();
}
}
_ => (),
}
}
// Remove false cases
cases.retain(|_, list| {
// Remove all entries that have false conditions
list.retain(|index| match case_blocks[*index].condition {
Expr::BoolConstant(false, ..) => {
list.retain(|index| {
if case_blocks[*index].is_always_false() {
state.set_dirty();
false
} else {
true
}
_ => true,
});
// Remove all entries after a `true` condition
if let Some(n) = list
.iter()
.find(|&&index| match case_blocks[index].condition {
Expr::BoolConstant(true, ..) => true,
_ => false,
})
.find(|&&index| case_blocks[index].is_always_true())
{
if n + 1 < list.len() {
state.set_dirty();
@ -779,12 +751,13 @@ fn optimize_stmt(stmt: &mut Stmt, state: &mut OptimizerState, preserve_result: b
});
// Remove false ranges
ranges.retain(|r| match case_blocks[r.index()].condition {
Expr::BoolConstant(false, ..) => {
ranges.retain(|r| {
if case_blocks[r.index()].is_always_false() {
state.set_dirty();
false
} else {
true
}
_ => true,
});
if let Some(index) = def_case {