Allow the preprocessor to cache the lexed tokens, so that we can do efficient lookahead and backtracking.

1) New public methods added:
  -EnableBacktrackAtThisPos
  -DisableBacktrack
  -Backtrack
  -isBacktrackEnabled

2) LookAhead() implementation is replaced with a more efficient one.
3) LookNext() is removed.

llvm-svn: 54611

1 files changed, 3 insertions, 1 deletions

diff --git a/clang/lib/Lex/Preprocessor.cpp b/clang/lib/Lex/Preprocessor.cpp
index 631b8361e90..33c94b6e8ad 100644
--- a/clang/lib/Lex/Preprocessor.cpp
+++ b/clang/lib/Lex/Preprocessor.cpp
@@ -68,6 +68,9 @@ Preprocessor::Preprocessor(Diagnostic &diags, const LangOptions &opts,
   InMacroArgs = false;
   NumCachedTokenLexers = 0;
 
+  CacheTokens = false;
+  CachedLexPos = 0;
+
   // "Poison" __VA_ARGS__, which can only appear in the expansion of a macro.
   // This gets unpoisoned where it is allowed.
   (Ident__VA_ARGS__ = getIdentifierInfo("__VA_ARGS__"))->setIsPoisoned();
@@ -579,4 +582,3 @@ void Preprocessor::HandleIdentifier(Token &Identifier) {
   if (II.isExtensionToken() && Features.C99) 
     Diag(Identifier, diag::ext_token_used);
 }
-