1 files changed, 7 insertions, 4 deletions
diff --git a/lib/CodeGen/TargetInfo.h b/lib/CodeGen/TargetInfo.h
index 913a1b068b..bb50ce69e3 100644
--- a/lib/CodeGen/TargetInfo.h
+++ b/lib/CodeGen/TargetInfo.h
@@ -158,10 +158,13 @@ namespace clang {
     ///   - the conventions are substantively different in how they pass
     ///     arguments, because in this case using the variadic convention
     ///     will lead to C99 violations.
-    /// It is not necessarily correct when arguments are passed in the
-    /// same way and some out-of-band information is passed for the
-    /// benefit of variadic callees, as is the case for x86-64.
-    /// In this case the ABI should be consulted.
+    ///
+    /// However, some platforms make the conventions identical except
+    /// for passing additional out-of-band information to a variadic
+    /// function: for example, x86-64 passes the number of SSE
+    /// arguments in %al.  On these platforms, it is desireable to
+    /// call unprototyped functions using the variadic convention so
+    /// that unprototyped calls to varargs functions still succeed.
     virtual bool isNoProtoCallVariadic(const CodeGen::CallArgList &args,
                                        const FunctionNoProtoType *fnType) const;
   };