[OpenCL] Add LangAS::opencl_private to represent private address space in AST

Currently Clang uses default address space (0) to represent private address space for OpenCL
in AST. There are two issues with this:

Multiple address spaces including private address space cannot be diagnosed.
There is no mangling for default address space. For example, if private int* is emitted as
i32 addrspace(5)* in IR. It is supposed to be mangled as PUAS5i but it is mangled as
Pi instead.

This patch attempts to represent OpenCL private address space explicitly in AST. It adds
a new enum LangAS::opencl_private and adds it to the variable types which are implicitly
private:

automatic variables without address space qualifier

function parameter

pointee type without address space qualifier (OpenCL 1.2 and below)

Differential Revision: https://reviews.llvm.org/D35082

llvm-svn: 315668
diff --git a/clang/lib/AST/ItaniumMangle.cpp b/clang/lib/AST/ItaniumMangle.cpp
index cbad6e2..b4dc46a 100644
--- a/clang/lib/AST/ItaniumMangle.cpp
+++ b/clang/lib/AST/ItaniumMangle.cpp
@@ -2227,15 +2227,17 @@
     if (Context.getASTContext().addressSpaceMapManglingFor(AS)) {
       //  <target-addrspace> ::= "AS" <address-space-number>
       unsigned TargetAS = Context.getASTContext().getTargetAddressSpace(AS);
-      ASString = "AS" + llvm::utostr(TargetAS);
+      if (TargetAS != 0)
+        ASString = "AS" + llvm::utostr(TargetAS);
     } else {
       switch (AS) {
       default: llvm_unreachable("Not a language specific address space");
-      //  <OpenCL-addrspace> ::= "CL" [ "global" | "local" | "constant |
-      //                                "generic" ]
+      //  <OpenCL-addrspace> ::= "CL" [ "global" | "local" | "constant" |
+      //                                "private"| "generic" ]
       case LangAS::opencl_global:   ASString = "CLglobal";   break;
       case LangAS::opencl_local:    ASString = "CLlocal";    break;
       case LangAS::opencl_constant: ASString = "CLconstant"; break;
+      case LangAS::opencl_private:  ASString = "CLprivate";  break;
       case LangAS::opencl_generic:  ASString = "CLgeneric";  break;
       //  <CUDA-addrspace> ::= "CU" [ "device" | "constant" | "shared" ]
       case LangAS::cuda_device:     ASString = "CUdevice";   break;
@@ -2243,7 +2245,8 @@
       case LangAS::cuda_shared:     ASString = "CUshared";   break;
       }
     }
-    mangleVendorQualifier(ASString);
+    if (!ASString.empty())
+      mangleVendorQualifier(ASString);
   }
 
   // The ARC ownership qualifiers start with underscores.