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Loop instead of recursion #78292

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Oct 24, 2020
Merged

Loop instead of recursion #78292

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150 changes: 79 additions & 71 deletions compiler/rustc_ast_lowering/src/pat.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -10,82 +10,90 @@ use rustc_span::symbol::Ident;
use rustc_span::{source_map::Spanned, Span};

impl<'a, 'hir> LoweringContext<'a, 'hir> {
crate fn lower_pat(&mut self, p: &Pat) -> &'hir hir::Pat<'hir> {
crate fn lower_pat(&mut self, mut pattern: &Pat) -> &'hir hir::Pat<'hir> {
ensure_sufficient_stack(|| {
let node = match p.kind {
PatKind::Wild => hir::PatKind::Wild,
PatKind::Ident(ref binding_mode, ident, ref sub) => {
let lower_sub = |this: &mut Self| sub.as_ref().map(|s| this.lower_pat(&*s));
let node = self.lower_pat_ident(p, binding_mode, ident, lower_sub);
node
}
PatKind::Lit(ref e) => hir::PatKind::Lit(self.lower_expr(e)),
PatKind::TupleStruct(ref path, ref pats) => {
let qpath = self.lower_qpath(
p.id,
&None,
path,
ParamMode::Optional,
ImplTraitContext::disallowed(),
);
let (pats, ddpos) = self.lower_pat_tuple(pats, "tuple struct");
hir::PatKind::TupleStruct(qpath, pats, ddpos)
}
PatKind::Or(ref pats) => hir::PatKind::Or(
self.arena.alloc_from_iter(pats.iter().map(|x| self.lower_pat(x))),
),
PatKind::Path(ref qself, ref path) => {
let qpath = self.lower_qpath(
p.id,
qself,
path,
ParamMode::Optional,
ImplTraitContext::disallowed(),
);
hir::PatKind::Path(qpath)
}
PatKind::Struct(ref path, ref fields, etc) => {
let qpath = self.lower_qpath(
p.id,
&None,
path,
ParamMode::Optional,
ImplTraitContext::disallowed(),
);
// loop here to avoid recursion
let node = loop {
match pattern.kind {
PatKind::Wild => break hir::PatKind::Wild,
PatKind::Ident(ref binding_mode, ident, ref sub) => {
let lower_sub = |this: &mut Self| sub.as_ref().map(|s| this.lower_pat(&*s));
break self.lower_pat_ident(pattern, binding_mode, ident, lower_sub);
}
PatKind::Lit(ref e) => break hir::PatKind::Lit(self.lower_expr(e)),
PatKind::TupleStruct(ref path, ref pats) => {
let qpath = self.lower_qpath(
pattern.id,
&None,
path,
ParamMode::Optional,
ImplTraitContext::disallowed(),
);
let (pats, ddpos) = self.lower_pat_tuple(pats, "tuple struct");
break hir::PatKind::TupleStruct(qpath, pats, ddpos);
}
PatKind::Or(ref pats) => {
break hir::PatKind::Or(
self.arena.alloc_from_iter(pats.iter().map(|x| self.lower_pat(x))),
);
}
PatKind::Path(ref qself, ref path) => {
let qpath = self.lower_qpath(
pattern.id,
qself,
path,
ParamMode::Optional,
ImplTraitContext::disallowed(),
);
break hir::PatKind::Path(qpath);
}
PatKind::Struct(ref path, ref fields, etc) => {
let qpath = self.lower_qpath(
pattern.id,
&None,
path,
ParamMode::Optional,
ImplTraitContext::disallowed(),
);

let fs = self.arena.alloc_from_iter(fields.iter().map(|f| hir::FieldPat {
hir_id: self.next_id(),
ident: f.ident,
pat: self.lower_pat(&f.pat),
is_shorthand: f.is_shorthand,
span: f.span,
}));
hir::PatKind::Struct(qpath, fs, etc)
}
PatKind::Tuple(ref pats) => {
let (pats, ddpos) = self.lower_pat_tuple(pats, "tuple");
hir::PatKind::Tuple(pats, ddpos)
}
PatKind::Box(ref inner) => hir::PatKind::Box(self.lower_pat(inner)),
PatKind::Ref(ref inner, mutbl) => hir::PatKind::Ref(self.lower_pat(inner), mutbl),
PatKind::Range(ref e1, ref e2, Spanned { node: ref end, .. }) => {
hir::PatKind::Range(
e1.as_deref().map(|e| self.lower_expr(e)),
e2.as_deref().map(|e| self.lower_expr(e)),
self.lower_range_end(end, e2.is_some()),
)
}
PatKind::Slice(ref pats) => self.lower_pat_slice(pats),
PatKind::Rest => {
// If we reach here the `..` pattern is not semantically allowed.
self.ban_illegal_rest_pat(p.span)
let fs = self.arena.alloc_from_iter(fields.iter().map(|f| hir::FieldPat {
hir_id: self.next_id(),
ident: f.ident,
pat: self.lower_pat(&f.pat),
is_shorthand: f.is_shorthand,
span: f.span,
}));
break hir::PatKind::Struct(qpath, fs, etc);
}
PatKind::Tuple(ref pats) => {
let (pats, ddpos) = self.lower_pat_tuple(pats, "tuple");
break hir::PatKind::Tuple(pats, ddpos);
}
PatKind::Box(ref inner) => {
break hir::PatKind::Box(self.lower_pat(inner));
}
PatKind::Ref(ref inner, mutbl) => {
break hir::PatKind::Ref(self.lower_pat(inner), mutbl);
}
PatKind::Range(ref e1, ref e2, Spanned { node: ref end, .. }) => {
break hir::PatKind::Range(
e1.as_deref().map(|e| self.lower_expr(e)),
e2.as_deref().map(|e| self.lower_expr(e)),
self.lower_range_end(end, e2.is_some()),
);
}
PatKind::Slice(ref pats) => break self.lower_pat_slice(pats),
PatKind::Rest => {
// If we reach here the `..` pattern is not semantically allowed.
break self.ban_illegal_rest_pat(pattern.span);
}
// return inner to be processed in next loop
PatKind::Paren(ref inner) => pattern = inner,
PatKind::MacCall(_) => panic!("{:?} shouldn't exist here", pattern.span),
}
// FIXME: consider not using recursion to lower this.
PatKind::Paren(ref inner) => return self.lower_pat(inner),
PatKind::MacCall(_) => panic!("{:?} shouldn't exist here", p.span),
};

self.pat_with_node_id_of(p, node)
self.pat_with_node_id_of(pattern, node)
})
}

Expand Down