bjoernager/rust
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Remove the lookahead buffer.

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This commit is contained in:
Jeffrey Seyfried 2017-01-14 11:13:45 +00:00
parent 57c0ed097c
commit 4c98e1bc59
1 changed files with 14 additions and 37 deletions
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51
src/libsyntax/parse/parser.rs
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@ -156,22 +156,6 @@ enum PrevTokenKind {
Other,
}
// Simple circular buffer used for keeping few next tokens.
#[derive(Default)]
struct LookaheadBuffer {
buffer: [TokenAndSpan; LOOKAHEAD_BUFFER_CAPACITY],
start: usize,
end: usize,
}
const LOOKAHEAD_BUFFER_CAPACITY: usize = 8;
impl LookaheadBuffer {
fn len(&self) -> usize {
(LOOKAHEAD_BUFFER_CAPACITY + self.end - self.start) % LOOKAHEAD_BUFFER_CAPACITY
}
}
/* ident is handled by common.rs */
pub struct Parser<'a> {
@ -184,7 +168,6 @@ pub struct Parser<'a> {
pub prev_span: Span,
/// the previous token kind
prev_token_kind: PrevTokenKind,
lookahead_buffer: LookaheadBuffer,
pub restrictions: Restrictions,
pub quote_depth: usize, // not (yet) related to the quasiquoter
parsing_token_tree: bool,
@ -281,7 +264,6 @@ impl<'a> Parser<'a> {
span: syntax_pos::DUMMY_SP,
prev_span: syntax_pos::DUMMY_SP,
prev_token_kind: PrevTokenKind::Other,
lookahead_buffer: Default::default(),
restrictions: Restrictions::empty(),
quote_depth: 0,
parsing_token_tree: false,
@ -875,14 +857,7 @@ impl<'a> Parser<'a> {
_ => PrevTokenKind::Other,
};
let next = if self.lookahead_buffer.start == self.lookahead_buffer.end {
self.next_tok()
} else {
// Avoid token copies with `replace`.
let old_start = self.lookahead_buffer.start;
self.lookahead_buffer.start = (old_start + 1) % LOOKAHEAD_BUFFER_CAPACITY;
mem::replace(&mut self.lookahead_buffer.buffer[old_start], Default::default())
};
let next = self.next_tok();
self.span = next.sp;
self.token = next.tok;
self.expected_tokens.clear();
@ -917,18 +892,20 @@ impl<'a> Parser<'a> {
F: FnOnce(&token::Token) -> R,
{
if dist == 0 {
f(&self.token)
} else if dist < LOOKAHEAD_BUFFER_CAPACITY {
while self.lookahead_buffer.len() < dist {
self.lookahead_buffer.buffer[self.lookahead_buffer.end] = self.next_tok();
self.lookahead_buffer.end =
(self.lookahead_buffer.end + 1) % LOOKAHEAD_BUFFER_CAPACITY;
}
let index = (self.lookahead_buffer.start + dist - 1) % LOOKAHEAD_BUFFER_CAPACITY;
f(&self.lookahead_buffer.buffer[index].tok)
} else {
self.bug("lookahead distance is too large");
return f(&self.token);
}
let mut tok = token::Eof;
if let Some(&(ref tts, mut i)) = self.tts.last() {
i += dist - 1;
if i < tts.len() {
tok = match tts.get_tt(i) {
TokenTree::Token(_, tok) => tok,
TokenTree::Delimited(_, delimited) => token::OpenDelim(delimited.delim),
TokenTree::Sequence(..) => token::Dollar,
};
}
}
f(&tok)
}
pub fn fatal(&self, m: &str) -> DiagnosticBuilder<'a> {
self.sess.span_diagnostic.struct_span_fatal(self.span, m)