[SYCL] Put string literals to private address space

Although OpenCL specification explicitly states that a string literal
should reside in constant address space, it does not work for SYCL
with "generic by default" address space rules.

For example:

   const char *getLiteral() {
     return "A";
   }

   void func(bool AorB) {
     char B[] = {'B', '\0'};
     const char* C = AorB ? A : B;
   }

If `A' reside in constant address space, it cannot be returned from a
function `getLiteral', because it returns a generic const char*.

Signed-off-by: Andrew Savonichev <andrew.savonichev@intel.com>

Author: Andrew Savonichev

clang/lib/CodeGen/CodeGenModule.cpp

@@ -3663,6 +3663,14 @@ LangAS CodeGenModule::getStringLiteralAddressSpace() const {
   // OpenCL v1.2 s6.5.3: a string literal is in the constant address space.
   if (LangOpts.OpenCL)
     return LangAS::opencl_constant;
+  if (LangOpts.SYCLIsDevice && !getenv("DISABLE_INFER_AS"))
+    // If we keep a literal string in constant address space, the following code
+    // becomes illegal:
+    //
+    //   const char *getLiteral() n{
+    //     return "AB";
+    //   }
+    return LangAS::opencl_private;
   if (auto AS = getTarget().getConstantAddressSpace())
     return AS.getValue();
   return LangAS::Default;

clang/test/CodeGenSYCL/address-space-new.cpp

@@ -1,19 +1,24 @@
-// RUN: DISABLE_INFER_AS=1 %clang_cc1 -triple spir64-unknown-linux-sycldevice  -std=c++11 -fsycl-is-device -disable-llvm-passes -emit-llvm -x c++ %s -o - | FileCheck %s --check-prefix=CHECK-LEGACY
-// RUN: %clang_cc1 -triple spir64-unknown-linux-sycldevice  -std=c++11 -fsycl-is-device -disable-llvm-passes -emit-llvm -x c++ %s -o - | FileCheck %s --check-prefix=CHECK-NEW
-
+// RUN: DISABLE_INFER_AS=1 %clang_cc1 -triple spir64-unknown-linux-sycldevice  -std=c++11 -fsycl-is-device -disable-llvm-passes -emit-llvm -x c++ %s -o - | FileCheck %s --check-prefixes=CHECK,CHECK-LEGACY
+// RUN: %clang_cc1 -triple spir64-unknown-linux-sycldevice  -std=c++11 -fsycl-is-device -disable-llvm-passes -emit-llvm -x c++ %s -o - | FileCheck %s --check-prefixes=CHECK,CHECK-NEW
 
 void test() {
   static const int foo = 0x42;
   // CHECK-LEGACY: @_ZZ4testvE3foo = internal constant i32 66, align 4
   // CHECK-NEW:    @_ZZ4testvE3foo = internal addrspace(1) constant i32 66, align 4
 
+  // CHECK: @[[STR:[.a-zA-Z0-9_]+]] = private unnamed_addr constant [14 x i8] c"Hello, world!\00", align 1
   int i = 0;
   int *pptr = &i;
   // CHECK-LEGACY: store i32* %i, i32** %pptr
   // CHECK-NEW: %[[GEN:[0-9]+]] = addrspacecast i32* %i to i32 addrspace(4)*
   // CHECK-NEW: store i32 addrspace(4)* %[[GEN]], i32 addrspace(4)** %pptr
-
   *pptr = foo;
+
+  const char *str = "Hello, world!";
+  // CHECK-LEGACY: store i8* getelementptr inbounds ([14 x i8], [14 x i8]* @[[STR]], i64 0, i64 0), i8** %{{.*}}, align 8
+  // CHECK-NEW: store i8 addrspace(4)* addrspacecast (i8* getelementptr inbounds ([14 x i8], [14 x i8]* @[[STR]], i64 0, i64 0) to i8 addrspace(4)*), i8 addrspace(4)** %{{.*}}, align 8
+
+  i = str[0];
 }