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replace boolean with lazy iteration

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Should probably check how this performs, but it's always nicer to
track just a bit less mutable state.
This commit is contained in:
Niko Matsakis 2019-09-19 10:07:50 -04:00
parent d95a7768a1
commit 9a447a232e
1 changed files with 20 additions and 19 deletions
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39
src/librustc_mir/build/scope.rs
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@ -104,19 +104,6 @@ struct Scope {
/// the span of that region_scope /// the span of that region_scope
region_scope_span: Span, region_scope_span: Span,
/// Whether there's anything to do for the cleanup path, that is,
/// when unwinding through this scope. This includes destructors,
/// but not StorageDead statements, which don't get emitted at all
/// for unwinding, for several reasons:
/// * clang doesn't emit llvm.lifetime.end for C++ unwinding
/// * LLVM's memory dependency analysis can't handle it atm
/// * polluting the cleanup MIR with StorageDead creates
/// landing pads even though there's no actual destructors
/// * freeing up stack space has no effect during unwinding
/// Note that for generators we do emit StorageDeads, for the
/// use of optimizations in the MIR generator transform.
needs_cleanup: bool,
/// set of places to drop when exiting this scope. This starts /// set of places to drop when exiting this scope. This starts
/// out empty but grows as variables are declared during the /// out empty but grows as variables are declared during the
/// building process. This is a stack, so we always drop from the /// building process. This is a stack, so we always drop from the
@ -261,6 +248,25 @@ impl Scope {
scope: self.source_scope scope: self.source_scope
} }
} }
/// Whether there's anything to do for the cleanup path, that is,
/// when unwinding through this scope. This includes destructors,
/// but not StorageDead statements, which don't get emitted at all
/// for unwinding, for several reasons:
/// * clang doesn't emit llvm.lifetime.end for C++ unwinding
/// * LLVM's memory dependency analysis can't handle it atm
/// * polluting the cleanup MIR with StorageDead creates
/// landing pads even though there's no actual destructors
/// * freeing up stack space has no effect during unwinding
/// Note that for generators we do emit StorageDeads, for the
/// use of optimizations in the MIR generator transform.
fn needs_cleanup(&self) -> bool {
self.drops.iter().any(|drop| match drop.kind {
DropKind::Value => true,
DropKind::Storage => false,
})
}
} }
impl<'tcx> Scopes<'tcx> { impl<'tcx> Scopes<'tcx> {
@ -274,7 +280,6 @@ impl<'tcx> Scopes<'tcx> {
source_scope: vis_scope, source_scope: vis_scope,
region_scope: region_scope.0, region_scope: region_scope.0,
region_scope_span: region_scope.1.span, region_scope_span: region_scope.1.span,
needs_cleanup: false,
drops: vec![], drops: vec![],
cached_generator_drop: None, cached_generator_drop: None,
cached_exits: Default::default(), cached_exits: Default::default(),
@ -295,7 +300,7 @@ impl<'tcx> Scopes<'tcx> {
fn may_panic(&self, scope_count: usize) -> bool { fn may_panic(&self, scope_count: usize) -> bool {
let len = self.len(); let len = self.len();
self.scopes[(len - scope_count)..].iter().any(|s| s.needs_cleanup) self.scopes[(len - scope_count)..].iter().any(|s| s.needs_cleanup())
} }
/// Finds the breakable scope for a given label. This is used for /// Finds the breakable scope for a given label. This is used for
@ -801,10 +806,6 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
// cache of outer scope stays intact. // cache of outer scope stays intact.
scope.invalidate_cache(!needs_drop, self.is_generator, this_scope); scope.invalidate_cache(!needs_drop, self.is_generator, this_scope);
if this_scope { if this_scope {
if let DropKind::Value = drop_kind {
scope.needs_cleanup = true;
}
let region_scope_span = region_scope.span(self.hir.tcx(), let region_scope_span = region_scope.span(self.hir.tcx(),
&self.hir.region_scope_tree); &self.hir.region_scope_tree);
// Attribute scope exit drops to scope's closing brace. // Attribute scope exit drops to scope's closing brace.