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change how we declare bindings so that unreachable arms don't

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cause panics
This commit is contained in:
Niko Matsakis 2015-09-29 16:17:40 -04:00
parent 96a3cd0679
commit 0197f982b2
2 changed files with 39 additions and 42 deletions
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75
src/librustc_mir/build/matches/mod.rs
View File

@ -34,6 +34,15 @@ pub fn match_expr(&mut self,
let discriminant_lvalue =
unpack!(block = self.as_lvalue(block, discriminant));
// Before we do anything, create uninitialized variables with
// suitable extent for all of the bindings in this match. It's
// easiest to do this up front because some of these arms may
// be unreachable or reachable multiple times.
let var_extent = self.extent_of_innermost_scope().unwrap();
for arm in &arms {
self.declare_bindings(var_extent, arm.patterns[0].clone());
}
let mut arm_blocks = ArmBlocks {
blocks: arms.iter()
.map(|_| self.cfg.start_new_block())
@ -52,14 +61,13 @@ pub fn match_expr(&mut self,
// reverse of the order in which candidates are written in the
// source.
let candidates: Vec<Candidate<H>> =
arms.into_iter()
arms.iter()
.enumerate()
.rev() // highest priority comes last
.flat_map(|(arm_index, arm)| {
let guard = arm.guard;
arm.patterns.into_iter()
arm.patterns.iter()
.rev()
.map(move |pat| (arm_index, pat, guard.clone()))
.map(move |pat| (arm_index, pat.clone(), arm.guard.clone()))
})
.map(|(arm_index, pattern, guard)| {
Candidate {
@ -73,8 +81,7 @@ pub fn match_expr(&mut self,
// this will generate code to test discriminant_lvalue and
// branch to the appropriate arm block
let var_extent = self.extent_of_innermost_scope().unwrap();
self.match_candidates(span, var_extent, &mut arm_blocks, candidates, block);
self.match_candidates(span, &mut arm_blocks, candidates, block);
// all the arm blocks will rejoin here
let end_block = self.cfg.start_new_block();
@ -123,9 +130,12 @@ pub fn lvalue_into_pattern(&mut self,
initializer: &Lvalue<H>)
-> BlockAnd<()>
{
// first, creating the bindings
self.declare_bindings(var_extent, irrefutable_pat.clone());
// create a dummy candidate
let mut candidate = Candidate::<H> {
match_pairs: vec![self.match_pair(initializer.clone(), irrefutable_pat)],
match_pairs: vec![self.match_pair(initializer.clone(), irrefutable_pat.clone())],
bindings: vec![],
guard: None,
arm_index: 0, // since we don't call `match_candidates`, this field is unused
@ -143,12 +153,12 @@ pub fn lvalue_into_pattern(&mut self,
}
// now apply the bindings, which will also declare the variables
self.bind_matched_candidate(block, var_extent, candidate.bindings);
self.bind_matched_candidate(block, candidate.bindings);
block.unit()
}
pub fn declare_uninitialized_variables(&mut self,
pub fn declare_bindings(&mut self,
var_extent: H::CodeExtent,
pattern: PatternRef<H>)
{
@ -157,24 +167,24 @@ pub fn declare_uninitialized_variables(&mut self,
PatternKind::Binding { mutability, name, mode: _, var, ty, subpattern } => {
self.declare_binding(var_extent, mutability, name, var, ty, pattern.span);
if let Some(subpattern) = subpattern {
self.declare_uninitialized_variables(var_extent, subpattern);
self.declare_bindings(var_extent, subpattern);
}
}
PatternKind::Array { prefix, slice, suffix } |
PatternKind::Slice { prefix, slice, suffix } => {
for subpattern in prefix.into_iter().chain(slice).chain(suffix) {
self.declare_uninitialized_variables(var_extent, subpattern);
self.declare_bindings(var_extent, subpattern);
}
}
PatternKind::Constant { .. } | PatternKind::Range { .. } | PatternKind::Wild => {
}
PatternKind::Deref { subpattern } => {
self.declare_uninitialized_variables(var_extent, subpattern);
self.declare_bindings(var_extent, subpattern);
}
PatternKind::Leaf { subpatterns } |
PatternKind::Variant { subpatterns, .. } => {
for subpattern in subpatterns {
self.declare_uninitialized_variables(var_extent, subpattern.pattern);
self.declare_bindings(var_extent, subpattern.pattern);
}
}
}
@ -249,13 +259,12 @@ struct Test<H:Hair> {
impl<H:Hair> Builder<H> {
fn match_candidates(&mut self,
span: H::Span,
var_extent: H::CodeExtent,
arm_blocks: &mut ArmBlocks,
mut candidates: Vec<Candidate<H>>,
mut block: BasicBlock)
{
debug!("matched_candidate(span={:?}, var_extent={:?}, block={:?}, candidates={:?})",
span, var_extent, block, candidates);
debug!("matched_candidate(span={:?}, block={:?}, candidates={:?})",
span, block, candidates);
// Start by simplifying candidates. Once this process is
// complete, all the match pairs which remain require some
@ -275,8 +284,7 @@ fn match_candidates(&mut self,
// If so, apply any bindings, test the guard (if any), and
// branch to the arm.
let candidate = candidates.pop().unwrap();
if let Some(b) = self.bind_and_guard_matched_candidate(block, var_extent,
arm_blocks, candidate) {
if let Some(b) = self.bind_and_guard_matched_candidate(block, arm_blocks, candidate) {
block = b;
} else {
// if None is returned, then any remaining candidates
@ -309,7 +317,7 @@ fn match_candidates(&mut self,
candidate))
})
.collect();
self.match_candidates(span, var_extent, arm_blocks, applicable_candidates, target_block);
self.match_candidates(span, arm_blocks, applicable_candidates, target_block);
}
}
@ -327,16 +335,15 @@ fn match_candidates(&mut self,
/// MIR).
fn bind_and_guard_matched_candidate(&mut self,
mut block: BasicBlock,
var_extent: H::CodeExtent,
arm_blocks: &mut ArmBlocks,
candidate: Candidate<H>)
-> Option<BasicBlock> {
debug!("bind_and_guard_matched_candidate(block={:?}, var_extent={:?}, candidate={:?})",
block, var_extent, candidate);
debug!("bind_and_guard_matched_candidate(block={:?}, candidate={:?})",
block, candidate);
debug_assert!(candidate.match_pairs.is_empty());
self.bind_matched_candidate(block, var_extent, candidate.bindings);
self.bind_matched_candidate(block, candidate.bindings);
let arm_block = arm_blocks.blocks[candidate.arm_index];
@ -356,26 +363,16 @@ fn bind_and_guard_matched_candidate(&mut self,
fn bind_matched_candidate(&mut self,
block: BasicBlock,
var_extent: H::CodeExtent,
bindings: Vec<Binding<H>>) {
debug!("bind_matched_candidate(block={:?}, var_extent={:?}, bindings={:?})",
block, var_extent, bindings);
debug!("bind_matched_candidate(block={:?}, bindings={:?})",
block, bindings);
// Assign each of the bindings. This may trigger moves out of the candidate.
for binding in bindings {
// Create a variable for the `var_id` being bound. In the
// case where there are multiple patterns for a single
// arm, it may already exist.
let var_index = if !self.var_indices.contains_key(&binding.var_id) {
self.declare_binding(var_extent,
binding.mutability,
binding.name,
binding.var_id,
binding.var_ty,
binding.span)
} else {
self.var_indices[&binding.var_id]
};
// Find the variable for the `var_id` being bound. It
// should have been created by a previous call to
// `declare_bindings`.
let var_index = self.var_indices[&binding.var_id];
let rvalue = match binding.binding_mode {
BindingMode::ByValue =>

2
src/librustc_mir/build/stmt.rs
View File

@ -40,7 +40,7 @@ pub fn stmt(&mut self, mut block: BasicBlock, stmt: StmtRef<H>) -> BlockAnd<()>
StmtKind::Let { remainder_scope, init_scope, pattern, initializer: None, stmts } => {
this.in_scope(remainder_scope, block, |this| {
unpack!(block = this.in_scope(init_scope, block, |this| {
this.declare_uninitialized_variables(remainder_scope, pattern);
this.declare_bindings(remainder_scope, pattern);
block.unit()
}));
this.stmts(block, stmts)