Fix Windows codegen (LLVM globals) in non-singlemodule mode (crystal-…

…lang#8978)

Windows compilation so far was always being done in --single-module mode because --cross-compile implies it. But if one adds enough workarounds to try out the compiler *on* Windows, they would run into these problems, unless --single-module is specified.

* Problem 1:

  `__CxxFrameHandler3` is being added only in the main module but can be used in any other module, and the attempt would cause an error:

      Undefined llvm function: __CxxFrameHandler3

  Instead, define this function once per module (still on-demand).

* Problem 2:

  `void_ptr_type_descriptor` is being defined as an LLVM global once per module. But because it's the exact same symbol in all the modules, linking them together leads to this error (repeated per module):

      I-O-5858F-ileD-escriptor43.o : error LNK2005: "void *`RTTI Type Descriptor'" (??_R0PEAX@8) already defined in _main.o.

  Instead, define it only in the main module (still on-demand) and then let other modules refer to it as an external constant.

src/compiler/crystal/codegen/codegen.cr

@@ -183,9 +183,7 @@ module Crystal
 
       if @program.has_flag? "windows"
         @personality_name = "__CxxFrameHandler3"
-
-        personality_function = @llvm_mod.functions.add(@personality_name, [] of LLVM::Type, llvm_context.int32, true)
-        @main.personality_function = personality_function
+        @main.personality_function = windows_personality_fun
       else
         @personality_name = "__crystal_personality"
       end

src/compiler/crystal/codegen/exception.cr

@@ -62,7 +62,7 @@ class Crystal::CodeGenVisitor
 
     windows = @program.has_flag? "windows"
 
-    context.fun.personality_function = @llvm_mod.functions[@personality_name] if windows
+    context.fun.personality_function = windows_personality_fun if windows
 
     # This is the block which is entered when the body raises an exception
     rescue_block = new_block "rescue"
@@ -314,4 +314,10 @@ class Crystal::CodeGenVisitor
       @llvm_mod.functions.add("_CxxThrowException", [llvm_context.void_pointer, llvm_context.void_pointer], llvm_context.void, false)
     end
   end
+
+  private def windows_personality_fun
+    @llvm_mod.functions["__CxxFrameHandler3"]? || begin
+      @llvm_mod.functions.add("__CxxFrameHandler3", [] of LLVM::Type, llvm_context.int32, true)
+    end
+  end
 end

src/compiler/crystal/codegen/primitives.cr

@@ -1278,32 +1278,45 @@ class Crystal::CodeGenVisitor
   def void_ptr_type_descriptor
     void_ptr_type_descriptor_name = "\u{1}??_R0PEAX@8"
 
-    @llvm_mod.globals[void_ptr_type_descriptor_name]? || begin
+    if existing = @llvm_mod.globals[void_ptr_type_descriptor_name]?
+      return existing
+    end
+
+    type_descriptor = llvm_context.struct([
+      llvm_context.void_pointer.pointer,
+      llvm_context.void_pointer,
+      llvm_context.int8.array(6),
+    ])
+
+    if !@main_mod.globals[void_ptr_type_descriptor_name]?
       base_type_descriptor = external_constant(llvm_context.void_pointer, "\u{1}??_7type_info@@6B@")
 
       # .PEAX is void*
-      void_ptr_type_descriptor = @llvm_mod.globals.add(
-        llvm_context.struct([
-          llvm_context.void_pointer.pointer,
-          llvm_context.void_pointer,
-          llvm_context.int8.array(6),
-        ]), void_ptr_type_descriptor_name)
+      void_ptr_type_descriptor = @main_mod.globals.add(
+        type_descriptor, void_ptr_type_descriptor_name)
       void_ptr_type_descriptor.initializer = llvm_context.const_struct [
         base_type_descriptor,
         llvm_context.void_pointer.null,
         llvm_context.const_string(".PEAX"),
       ]
-
-      void_ptr_type_descriptor
     end
+
+    # if @llvm_mod == @main_mod, this will find the previously created void_ptr_type_descriptor
+    external_constant(type_descriptor, void_ptr_type_descriptor_name)
   end
 
   def void_ptr_throwinfo
     void_ptr_throwinfo_name = "_TI1PEAX"
 
-    @llvm_mod.globals[void_ptr_throwinfo_name]? || begin
+    if existing = @llvm_mod.globals[void_ptr_throwinfo_name]?
+      return existing
+    end
+
+    eh_throwinfo = llvm_context.struct([llvm_context.int32, llvm_context.int32, llvm_context.int32, llvm_context.int32])
+
+    if !@main_mod.globals[void_ptr_throwinfo_name]?
       catchable_type = llvm_context.struct([llvm_context.int32, llvm_context.int32, llvm_context.int32, llvm_context.int32, llvm_context.int32, llvm_context.int32, llvm_context.int32])
-      void_ptr_catchable_type = @llvm_mod.globals.add(
+      void_ptr_catchable_type = @main_mod.globals.add(
         catchable_type, "_CT??_R0PEAX@88")
       void_ptr_catchable_type.initializer = llvm_context.const_struct [
         int32(1),
@@ -1316,25 +1329,25 @@ class Crystal::CodeGenVisitor
       ]
 
       catchable_type_array = llvm_context.struct([llvm_context.int32, llvm_context.int32.array(1)])
-      catchable_void_ptr = @llvm_mod.globals.add(
+      catchable_void_ptr = @main_mod.globals.add(
         catchable_type_array, "_CTA1PEAX")
       catchable_void_ptr.initializer = llvm_context.const_struct [
         int32(1),
         llvm_context.int32.const_array([sub_image_base(void_ptr_catchable_type)]),
       ]
 
-      eh_throwinfo = llvm_context.struct([llvm_context.int32, llvm_context.int32, llvm_context.int32, llvm_context.int32])
-      void_ptr_throwinfo = @llvm_mod.globals.add(
+      void_ptr_throwinfo = @main_mod.globals.add(
         eh_throwinfo, void_ptr_throwinfo_name)
       void_ptr_throwinfo.initializer = llvm_context.const_struct [
         int32(0),
         int32(0),
         int32(0),
         sub_image_base(catchable_void_ptr),
       ]
-
-      void_ptr_throwinfo
     end
+
+    # if @llvm_mod == @main_mod, this will find the previously created void_ptr_throwinfo
+    external_constant(eh_throwinfo, void_ptr_throwinfo_name)
   end
 
   def external_constant(type, name)