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Commit100f3fd

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Add a new special case toParser::look_ahead.
This new special case is simpler than the old special case because itonly is used when `dist == 1`. But that's still enough to cover ~98% ofcases. This results in equivalent performance to the old special case,and identical behaviour as the general case.
1 parentebe1305 commit100f3fd

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  • compiler/rustc_parse/src/parser

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‎compiler/rustc_parse/src/parser/mod.rs‎

Lines changed: 29 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -1118,6 +1118,35 @@ impl<'a> Parser<'a> {
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returnlooker(&self.token);
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}
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// Typically around 98% of the `dist > 0` cases have `dist == 1`, so we
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// have a fast special case for that.
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if dist ==1{
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// The index is zero because the tree cursor's index always points
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// to the next token to be gotten.
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matchself.token_cursor.tree_cursor.look_ahead(0){
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Some(tree) =>{
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// Indexing stayed within the current token tree.
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returnmatch tree{
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TokenTree::Token(token, _) =>looker(token),
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TokenTree::Delimited(dspan, _, delim, _) =>{
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looker(&Token::new(token::OpenDelim(*delim), dspan.open))
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}
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};
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}
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None =>{
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// The tree cursor lookahead went (one) past the end of the
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// current token tree. Try to return a close delimiter.
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ifletSome(&(_, span, _, delim)) =self.token_cursor.stack.last()
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&& delim !=Delimiter::Invisible
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{
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// We are not in the outermost token stream, so we have
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// delimiters. Also, those delimiters are not skipped.
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returnlooker(&Token::new(token::CloseDelim(delim), span.close));
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}
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}
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}
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}
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// Just clone the token cursor and use `next`, skipping delimiters as
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// necessary. Slow but simple.
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letmut cursor =self.token_cursor.clone();

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