Add comments for turning on byval

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@161702 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/CodeGen/TargetInfo.cpp b/lib/CodeGen/TargetInfo.cpp
index 752228e..2cd239c 100644
--- a/lib/CodeGen/TargetInfo.cpp
+++ b/lib/CodeGen/TargetInfo.cpp
@@ -2757,6 +2757,8 @@
     }
   }
 
+  // Turn on byval for APCS and AAPCS.
+  // FIXME: turn on byval for AAPCS_VFP for performance.
   if (getABIKind() == ARMABIInfo::APCS || getABIKind() == ARMABIInfo::AAPCS) {
     if (getContext().getTypeSizeInChars(Ty) > CharUnits::fromQuantity(64) ||
         getContext().getTypeAlign(Ty) > 64) {