Add Preprocessor::LookNext method, which implements an efficient way to 'take a peek' at the next token without consuming it.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@53375 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 26 insertions, 0 deletions

diff --git a/lib/Lex/PPLexerChange.cpp b/lib/Lex/PPLexerChange.cpp
index c15675114d..bef522e346 100644
--- a/lib/Lex/PPLexerChange.cpp
+++ b/lib/Lex/PPLexerChange.cpp
@@ -85,6 +85,10 @@ Token Preprocessor::LookAhead(unsigned N) {
   // 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.
+
+  // Optimized LookAhead(0) case.
+  if (N == 0)
+    return LookNext();
   
   Token *LookaheadTokens = new Token[N+1];
 
@@ -122,6 +126,28 @@ Token Preprocessor::LookAhead(unsigned N) {
   return Tok;
 }
 
+/// PeekToken - Lexes one token into PeekedToken and pushes CurLexer,

+/// CurLexerToken into the IncludeMacroStack before setting them to null.

+void Preprocessor::PeekToken() {

+  Lex(PeekedToken);

+  // Cache the current Lexer, TokenLexer and set them both to null.

+  // When Lex() is called, PeekedToken will be "consumed".

+  IncludeMacroStack.push_back(IncludeStackInfo(CurLexer, CurDirLookup,

+                                               CurTokenLexer));

+  CurLexer = 0;

+  CurTokenLexer = 0;

+}

+
+/// ConsumedPeekedToken - Called when Lex() is about to return the PeekedToken

+/// and have it "consumed".

+void Preprocessor::ConsumedPeekedToken() {

+  assert(PeekedToken.getLocation().isValid() && "Confused Peeking?");

+  // Restore CurLexer, TokenLexer.

+  RemoveTopOfLexerStack();

+  // Make PeekedToken invalid.

+  PeekedToken.startToken();

+}

+
 
 //===----------------------------------------------------------------------===//
 // Methods for Entering and Callbacks for leaving various contexts