[preprocessor] In Preprocessor::CachingLex() check whether there were more tokens

cached during the non-cached lex, otherwise we are going to drop them.

Fixes a bogus "_Pragma takes a parenthesized string literal" error when
expanding consecutive _Pragmas in a macro argument.

Part of rdar://11168596

llvm-svn: 153994

1 files changed, 11 insertions, 7 deletions

diff --git a/clang/lib/Lex/PPCaching.cpp b/clang/lib/Lex/PPCaching.cpp
index 0d5e34f0bfe..6f4c189b4f6 100644
--- a/clang/lib/Lex/PPCaching.cpp
+++ b/clang/lib/Lex/PPCaching.cpp
@@ -57,17 +57,21 @@ void Preprocessor::CachingLex(Token &Result) {
   ExitCachingLexMode();
   Lex(Result);
 
-  if (!isBacktrackEnabled()) {
+  if (isBacktrackEnabled()) {
+    // Cache the lexed token.
+    EnterCachingLexMode();
+    CachedTokens.push_back(Result);
+    ++CachedLexPos;
+    return;
+  }
+
+  if (CachedLexPos < CachedTokens.size()) {
+    EnterCachingLexMode();
+  } else {
     // All cached tokens were consumed.
     CachedTokens.clear();
     CachedLexPos = 0;
-    return;
   }
-
-  // Cache the lexed token.
-  EnterCachingLexMode();
-  CachedTokens.push_back(Result);
-  ++CachedLexPos;
 }
 
 void Preprocessor::EnterCachingLexMode() {