Handle readwrite constraints correctly

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@62043 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/test/CodeGen/asm.c b/test/CodeGen/asm.c
new file mode 100644
index 0000000..d6fbf77
--- /dev/null
+++ b/test/CodeGen/asm.c
@@ -0,0 +1,5 @@
+// RUN: clang %s -arch=i386 -verify -fsyntax-only
+void f(int len)
+{
+  __asm__ volatile("" :"=&r"(len), "+&r"(len));
+}