'true' in a CPP expression evaluates to 1 when in C++ mode. This implements

test/Preprocessor/cxx_true.cpp

llvm-svn: 39399

clang/Lex/PPExpressions.cpp

@@ -73,9 +73,10 @@ static bool EvaluateValue(APSInt &Result, LexerToken &PeekTok,
   // keywords are pp-identifiers, so we can't check the kind.
   if (IdentifierInfo *II = PeekTok.getIdentifierInfo()) {
     // If this identifier isn't 'defined' and it wasn't macro expanded, it turns
-    // into a simple 0.
+    // into a simple 0, unless it is the C++ keyword "true", in which case it
+    // turns into "1".
     if (II->getPPKeywordID() != tok::pp_defined) {
-      Result = 0;
+      Result = II->getTokenID() == tok::kw_true;
       Result.setIsUnsigned(false);  // "0" is signed intmax_t 0.
       PP.LexNonComment(PeekTok);
       return false;

clang/test/Preprocessor/cxx_true.cpp

@@ -0,0 +1,13 @@
+/* RUN: clang -E t.cpp -x=c++ | grep block_1 &&
+   RUN: clang -E t.cpp -x=c++ | not grep block_2 &&
+   RUN: clang -E t.cpp -x=c | not grep block
+*/
+
+#if true
+block_1
+#endif
+
+#if false
+block_2
+#endif
+