[CUDA] Allow external variables in separate compilation

According to the CUDA Programming Guide this is prohibited in
whole program compilation mode. This makes sense because external
references cannot be satisfied in that mode anyway. However,
such variables are allowed in separate compilation mode which
is a valid use case.

Differential Revision: https://reviews.llvm.org/D42923

llvm-svn: 325136

clang/lib/Sema/SemaDeclAttr.cpp

@@ -4112,7 +4112,8 @@ static void handleSharedAttr(Sema &S, Decl *D, const AttributeList &Attr) {
   auto *VD = cast<VarDecl>(D);
   // extern __shared__ is only allowed on arrays with no length (e.g.
   // "int x[]").
-  if (VD->hasExternalStorage() && !isa<IncompleteArrayType>(VD->getType())) {
+  if (!S.getLangOpts().CUDARelocatableDeviceCode && VD->hasExternalStorage() &&
+      !isa<IncompleteArrayType>(VD->getType())) {
     S.Diag(Attr.getLoc(), diag::err_cuda_extern_shared) << VD;
     return;
   }

clang/test/SemaCUDA/extern-shared.cu

@@ -1,6 +1,11 @@
 // RUN: %clang_cc1 -fsyntax-only -verify %s
 // RUN: %clang_cc1 -fsyntax-only -fcuda-is-device -verify %s
 
+// RUN: %clang_cc1 -fsyntax-only -fcuda-rdc -verify=rdc %s
+// RUN: %clang_cc1 -fsyntax-only -fcuda-is-device -fcuda-rdc -verify=rdc %s
+// These declarations are fine in separate compilation mode:
+// rdc-no-diagnostics
+
 #include "Inputs/cuda.h"
 
 __device__ void foo() {