Fix the dllimport code generation for opaque type

Added test cases to verify the 'dllimport' usage in LLVM IR.

Fixes: #1407

Author: kaadam

test/llvm_ir_correct/dllimport_test.f90

@@ -0,0 +1,24 @@
+! Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+! See https://llvm.org/LICENSE.txt for license information.
+! SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+!
+! https://github.com/flang-compiler/flang/issues/320
+! https://github.com/flang-compiler/flang/issues/1407
+!
+! The dllimport_test.f90 relies on 'dllimport_test.f90_mod.f90' external module
+! to test the presence of 'dllimport' storage class in LLVM IR
+! for external module and opaque type.
+!
+! REQUIRES: system-windows
+!
+! RUN: %flang -S -emit-llvm -S -emit-llvm %s_mod.f90 %s
+! RUN: cat dllimport_test.ll | FileCheck %s
+! CHECK: %structdllimport_module__t_type__td_ = type opaque
+! CHECK: @_dllimport_module_10_ = external dllimport global
+! CHECK: @dllimport_module__t_type__td_ = external dllimport global
+program h_main
+  use dllimport_module
+  implicit none
+
+  call foobar(array)
+end program

test/llvm_ir_correct/dllimport_test.f90_mod.f90

@@ -0,0 +1,33 @@
+!
+! Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+! See https://llvm.org/LICENSE.txt for license information.
+! SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+!
+! This file is compiled with other test dllimport_test.f90.
+! The dllimport_test.f90 relies on 'dllimport_test.f90_mod.f90' external module
+! to test the presence of 'dllimport' storage class in LLVM IR
+! for external module and opaque type.
+!
+! REQUIRES: system-windows
+! RUN: true
+
+module dllimport_module
+  implicit none
+
+  type t_type
+    private
+    integer :: a, b
+  end type
+
+  type(t_type), parameter :: array(2) = (/t_type(1, 1), t_type(1, 0)/)
+
+  interface foobar
+    module procedure test
+  end interface
+
+  contains
+  subroutine test(a)
+    type(t_type), dimension(:) :: a
+    return
+  end subroutine
+end module

tools/flang2/flang2exe/llassem.cpp

@@ -1202,8 +1202,13 @@ assemble_end(void)
   for (gblsym = ag_global; gblsym; gblsym = AG_SYMLK(gblsym)) {
     if (AG_TYPEDESC(gblsym) && !AG_DEFD(gblsym)) {
       fprintf(ASMFIL, "%%%s = type opaque\n", AG_TYPENAME(gblsym));
-      fprintf(ASMFIL, "@%s = external global %%%s\n", AG_NAME(gblsym),
-              AG_TYPENAME(gblsym));
+      if (strstr(cpu_llvm_module->target_triple, "windows-msvc") != NULL) {
+        fprintf(ASMFIL, "@%s = external dllimport global %%%s\n", AG_NAME(gblsym),
+                AG_TYPENAME(gblsym));
+      } else {
+        fprintf(ASMFIL, "@%s = external global %%%s\n", AG_NAME(gblsym),
+                AG_TYPENAME(gblsym));
+      }
     }
   }
   for (gblsym = ag_typedef; gblsym; gblsym = AG_SYMLK(gblsym)) {
@@ -1212,8 +1217,13 @@ assemble_end(void)
               AG_TYPENAME(gblsym));
     else if (AG_TYPEDESC(gblsym) && !AG_DEFD(gblsym)) {
       fprintf(ASMFIL, "%%%s = type opaque\n", AG_TYPENAME(gblsym));
-      fprintf(ASMFIL, "@%s = external global %%%s\n", AG_NAME(gblsym),
-              AG_TYPENAME(gblsym));
+      if (strstr(cpu_llvm_module->target_triple, "windows-msvc") != NULL) {
+        fprintf(ASMFIL, "@%s = external dllimport global %%%s\n", AG_NAME(gblsym),
+                AG_TYPENAME(gblsym));
+      } else {
+        fprintf(ASMFIL, "@%s = external global %%%s\n", AG_NAME(gblsym),
+                AG_TYPENAME(gblsym));
+      }
     }
   }
   for (gblsym = ag_other; gblsym; gblsym = AG_SYMLK(gblsym)) {