From acbad20a6865f26842a0956da87d5f077faa8d15 Mon Sep 17 00:00:00 2001
From: Quinton Miller <nicetas.c@gmail.com>
Date: Sun, 12 Dec 2021 12:10:24 +0800
Subject: [PATCH 1/2] Add `dllimport` storage class to external lib variables
 on Windows

---
 src/compiler/crystal/codegen/codegen.cr |  3 +++
 src/empty.cr                            |  2 +-
 src/lib_c.cr                            |  2 +-
 src/llvm/enums.cr                       | 14 ++++++++++++--
 src/llvm/lib_llvm.cr                    |  2 ++
 src/llvm/value_methods.cr               |  8 ++++++++
 6 files changed, 27 insertions(+), 4 deletions(-)

diff --git a/src/compiler/crystal/codegen/codegen.cr b/src/compiler/crystal/codegen/codegen.cr
index c4b0d6959bf5..e881f2365e57 100644
--- a/src/compiler/crystal/codegen/codegen.cr
+++ b/src/compiler/crystal/codegen/codegen.cr
@@ -1450,6 +1450,9 @@ module Crystal
       unless var
         var = llvm_mod.globals.add(llvm_c_return_type(type), name)
         var.linkage = LLVM::Linkage::External
+        if @program.has_flag?("win32") && @program.has_flag?("preview_dll")
+          var.dll_storage_class = LLVM::DLLStorageClass::DLLImport
+        end
         var.thread_local = thread_local
       end
       var
diff --git a/src/empty.cr b/src/empty.cr
index 35f988afb583..22de59dcbb57 100644
--- a/src/empty.cr
+++ b/src/empty.cr
@@ -1,7 +1,7 @@
 require "primitives"
 
 {% if flag?(:win32) %}
-  @[Link("libcmt")] # For `mainCRTStartup`
+  @[Link({{ flag?(:preview_dll) ? "msvcrt" : "libcmt" }})] # For `mainCRTStartup`
 {% end %}
 lib LibCrystalMain
   @[Raises]
diff --git a/src/lib_c.cr b/src/lib_c.cr
index 61d2fdf03b3b..343f2c56a42b 100644
--- a/src/lib_c.cr
+++ b/src/lib_c.cr
@@ -1,5 +1,5 @@
 {% if flag?(:win32) %}
-  @[Link("libcmt")]
+  @[Link({{ flag?(:preview_dll) ? "msvcrt" : "libcmt" }})]
 {% end %}
 lib LibC
   alias Char = UInt8
diff --git a/src/llvm/enums.cr b/src/llvm/enums.cr
index 0b6d0b035c2c..63e1c818c0e1 100644
--- a/src/llvm/enums.cr
+++ b/src/llvm/enums.cr
@@ -220,8 +220,8 @@ module LLVM
     Appending
     Internal
     Private
-    DLLImport
-    DLLExport
+    DLLImport # obsolete
+    DLLExport # obsolete
     ExternalWeak
     Ghost
     Common
@@ -229,6 +229,16 @@ module LLVM
     LinkerPrivateWeak
   end
 
+  enum DLLStorageClass
+    Default
+
+    # Function to be imported from DLL.
+    DLLImport
+
+    # Function to be accessible from DLL.
+    DLLExport
+  end
+
   enum IntPredicate
     EQ  = 32
     NE
diff --git a/src/llvm/lib_llvm.cr b/src/llvm/lib_llvm.cr
index 9a93274c1294..15eb86866a86 100644
--- a/src/llvm/lib_llvm.cr
+++ b/src/llvm/lib_llvm.cr
@@ -255,6 +255,8 @@ lib LibLLVM
   fun get_initializer = LLVMGetInitializer(global_var : ValueRef) : ValueRef
   fun set_linkage = LLVMSetLinkage(global : ValueRef, linkage : LLVM::Linkage)
   fun get_linkage = LLVMGetLinkage(global : ValueRef) : LLVM::Linkage
+  fun get_dll_storage_class = LLVMGetDLLStorageClass(global : ValueRef) : LLVM::DLLStorageClass
+  fun set_dll_storage_class = LLVMSetDLLStorageClass(global : ValueRef, storage_class : LLVM::DLLStorageClass)
   fun set_metadata = LLVMSetMetadata(value : ValueRef, kind_id : UInt32, node : ValueRef)
   fun set_target = LLVMSetTarget(mod : ModuleRef, triple : UInt8*)
   fun set_thread_local = LLVMSetThreadLocal(global_var : ValueRef, is_thread_local : Int32)
diff --git a/src/llvm/value_methods.cr b/src/llvm/value_methods.cr
index 30a2e2bb7df1..26f288b8dbf3 100644
--- a/src/llvm/value_methods.cr
+++ b/src/llvm/value_methods.cr
@@ -55,6 +55,14 @@ module LLVM::ValueMethods
     LibLLVM.get_linkage(self)
   end
 
+  def dll_storage_class=(storage_class)
+    LibLLVM.set_dll_storage_class(self, storage_class)
+  end
+
+  def dll_storage_class
+    LibLLVM.get_dll_storage_class(self)
+  end
+
   def call_convention=(call_convention)
     LibLLVM.set_instruction_call_convention(self, call_convention)
   end

From 3c10083a89709669628827890018dba22c576d2e Mon Sep 17 00:00:00 2001
From: Quinton Miller <nicetas.c@gmail.com>
Date: Sun, 12 Dec 2021 17:00:34 +0800
Subject: [PATCH 2/2] no need for getter

---
 src/llvm/lib_llvm.cr      | 1 -
 src/llvm/value_methods.cr | 4 ----
 2 files changed, 5 deletions(-)

diff --git a/src/llvm/lib_llvm.cr b/src/llvm/lib_llvm.cr
index 15eb86866a86..f633a9cf8277 100644
--- a/src/llvm/lib_llvm.cr
+++ b/src/llvm/lib_llvm.cr
@@ -255,7 +255,6 @@ lib LibLLVM
   fun get_initializer = LLVMGetInitializer(global_var : ValueRef) : ValueRef
   fun set_linkage = LLVMSetLinkage(global : ValueRef, linkage : LLVM::Linkage)
   fun get_linkage = LLVMGetLinkage(global : ValueRef) : LLVM::Linkage
-  fun get_dll_storage_class = LLVMGetDLLStorageClass(global : ValueRef) : LLVM::DLLStorageClass
   fun set_dll_storage_class = LLVMSetDLLStorageClass(global : ValueRef, storage_class : LLVM::DLLStorageClass)
   fun set_metadata = LLVMSetMetadata(value : ValueRef, kind_id : UInt32, node : ValueRef)
   fun set_target = LLVMSetTarget(mod : ModuleRef, triple : UInt8*)
diff --git a/src/llvm/value_methods.cr b/src/llvm/value_methods.cr
index 26f288b8dbf3..9c6985ae06f7 100644
--- a/src/llvm/value_methods.cr
+++ b/src/llvm/value_methods.cr
@@ -59,10 +59,6 @@ module LLVM::ValueMethods
     LibLLVM.set_dll_storage_class(self, storage_class)
   end
 
-  def dll_storage_class
-    LibLLVM.get_dll_storage_class(self)
-  end
-
   def call_convention=(call_convention)
     LibLLVM.set_instruction_call_convention(self, call_convention)
   end