diff options
| -rw-r--r-- | Lex/PPLexerChange.cpp | 18 |
1 files changed, 18 insertions, 0 deletions
diff --git a/Lex/PPLexerChange.cpp b/Lex/PPLexerChange.cpp index 95028501f7..bd0ff7f94a 100644 --- a/Lex/PPLexerChange.cpp +++ b/Lex/PPLexerChange.cpp @@ -68,6 +68,24 @@ Lexer *Preprocessor::getCurrentFileLexer() const { /// code paths if possible! /// Token Preprocessor::LookAhead(unsigned N) { + // FIXME: Optimize the case where multiple lookahead calls are used back to + // back. Consider if the the parser contained (dynamically): + // Lookahead(1); Lookahead(1); Lookahead(1) + // This would return the same token 3 times, but would end up making lots of + // token stream lexers to do it. To handle this common case, see if the top + // of the lexer stack is a TokenStreamLexer with macro expansion disabled. If + // so, see if it has 'N' tokens available in it. If so, just return the + // token. + + // FIXME: Optimize the case when the parser does multiple nearby lookahead + // calls. For example, consider: + // Lookahead(0); Lookahead(1); Lookahead(2); + // The previous optimization won't apply, and there won't be any space left in + // the array that was previously new'd. To handle this, always round up the + // size we new to a multiple of 16 tokens. If the previous buffer has space + // left, we can just grow it. This means we only have to do the new 1/16th as + // often. + Token *LookaheadTokens = new Token[N]; // Read N+1 tokens into LookaheadTokens. After this loop, Tok is the token |