bjoernager/rust
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This commit is contained in:
est31 2022-12-03 23:32:14 +01:00
parent 8cf521d80e
commit a2076dc0a6
1 changed files with 18 additions and 6 deletions
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24
compiler/rustc_hir_analysis/src/check/region.rs
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@ -250,13 +250,23 @@ fn resolve_expr<'tcx>(visitor: &mut RegionResolutionVisitor<'tcx>, expr: &'tcx h
ref l,
ref r,
) => {
// For shortcircuiting operators, mark the RHS as a terminating
// scope since it only executes conditionally.
// expr is a short circuiting operator (|| or &&). As its
// functionality can't be overridden by traits, it always
// processes bool sub-expressions. bools are Copy and thus we
// can drop any temporaries in evaluation (read) order
// (with the exception of potentially failing let expressions).
// We achieve this by enclosing the operands in a terminating
// scope, both the LHS and the RHS.
// We optimize this a little in the presence of chains.
// Chains like a && b && c get lowered to AND(AND(a, b), c).
// In here, b and c are RHS, while a is the only LHS operand in
// that chain. This holds true for longer chains as well: the
// leading operand is always the only LHS operand that is not a
// binop itself. Putting a binop like AND(a, b) into a
// terminating scope is not useful, thus we only put the LHS
// into a terminating scope if it is not a binop.
// If the LHS is not another binop itself of the same kind as ours,
// we also mark it as terminating, so that in && or || chains,
// the temporaries are dropped in order instead of the very first
// being dropped last. For the Let exception, see below.
let terminate_lhs = match l.kind {
hir::ExprKind::Let(_) => false,
hir::ExprKind::Binary(source_map::Spanned { node, .. }, ..)
@ -264,6 +274,8 @@ fn resolve_expr<'tcx>(visitor: &mut RegionResolutionVisitor<'tcx>, expr: &'tcx h
{
false
}
// If the LHS is not another binop itself of the same kind as
// the current binop, mark it as terminating.
_ => true,
};
if terminate_lhs {