r285631 - Add comment explaining this mysterious macro name.

[Richard Smith via cfe-commits]

Author: rsmith
Date: Mon Oct 31 15:25:52 2016
New Revision: 285631

URL: http://llvm.org/viewvc/llvm-project?rev=285631&view=rev
Log:
Add comment explaining this mysterious macro name.

Modified:
    cfe/trunk/lib/Frontend/InitPreprocessor.cpp

Modified: cfe/trunk/lib/Frontend/InitPreprocessor.cpp
URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/Frontend/InitPreprocessor.cpp?rev=285631&r1=285630&r2=285631&view=diff
==============================================================================
--- cfe/trunk/lib/Frontend/InitPreprocessor.cpp (original)
+++ cfe/trunk/lib/Frontend/InitPreprocessor.cpp Mon Oct 31 15:25:52 2016
@@ -992,6 +992,9 @@ static void InitializePredefinedMacros(c
   }
 
   if (TI.hasInt128Type() && LangOpts.CPlusPlus && LangOpts.GNUMode) {
+    // For each extended integer type, g++ defines a macro mapping the
+    // index of the type (0 in this case) in some list of extended types
+    // to the type.
     Builder.defineMacro("__GLIBCXX_TYPE_INT_N_0", "__int128");
     Builder.defineMacro("__GLIBCXX_BITSIZE_INT_N_0", "128");
   }