Fix PR2627, support for Q constraint.


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@54943 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Basic/Targets.cpp b/lib/Basic/Targets.cpp
index 3147aaa..b156fbf 100644
--- a/lib/Basic/Targets.cpp
+++ b/lib/Basic/Targets.cpp
@@ -550,7 +550,8 @@
     case 'A': // edx:eax.
     case 't': // top of floating point stack.
     case 'u': // second from top of floating point stack.
-    case 'q': // a, b, c, d registers or any integer register in 64-bit.
+    case 'q': // Any register accessible as [r]l: a, b, c, and d.
+    case 'Q': // Any register accessible as [r]h: a, b, c, and d.
     case 'Z': // 32-bit integer constant for use with zero-extending x86_64
               // instructions.
     case 'N': // unsigned 8-bit integer constant for use with in and out