Only define the type name table in the main LLVM module (#16260)

#15904 made every LLVM module that references the `#as` pseudo-method define its own copy of `__crystal_type_id_to_class_name_map`, when only one copy in the main LLVM module is sufficient.

This patch brings the total cache size of the compiler itself from 234 MB to 148 MB on my Windows machine, for example.

Author: HertzDevil

src/compiler/crystal/codegen/codegen.cr

@@ -1618,26 +1618,37 @@ module Crystal
     end
 
     def type_id_to_class_name(type_id)
-      map = llvm_mod.globals["__crystal_type_id_to_class_name_map"]? || create_type_id_to_class_name_map("__crystal_type_id_to_class_name_map")
+      map_name = "__crystal_type_id_to_class_name_map"
 
-      str_ptr = gep llvm_type(@program.string), map, type_id
+      global = @main_mod.globals[map_name]?
+      unless global
+        global = @main_mod.globals.add(@main_llvm_typer.llvm_type(@program.string).array(@program.llvm_id.@ids.size), map_name)
+        global.linkage = LLVM::Linkage::Internal if @single_module
+        global.initializer = create_type_id_to_class_name_map
+        global.global_constant = true
+      end
+
+      if @llvm_mod != @main_mod
+        global = @llvm_mod.globals[map_name]?
+        unless global
+          global = @llvm_mod.globals.add(@llvm_typer.llvm_type(@program.string).array(@program.llvm_id.@ids.size), map_name)
+          global.linkage = LLVM::Linkage::External
+          global.global_constant = true
+        end
+      end
+
+      str_ptr = gep llvm_type(@program.string).array(@program.llvm_id.@ids.size), global, 0, type_id
       load llvm_type(@program.string), str_ptr
     end
 
-    def create_type_id_to_class_name_map(name)
+    def create_type_id_to_class_name_map
       ids = @program.llvm_id.@ids
       id_map = Array(LLVM::Value).new(size: ids.size, value: LLVM::Value.null)
       ids.each do |type, (_, type_id)|
-        id_map[type_id] = build_string_constant(type.to_s)
+        id_map[type_id] = build_string_constant(type.to_s, llvm_mod: @main_mod, llvm_typer: @main_llvm_typer)
       end
 
-      type = llvm_type(@program.string).array(ids.size)
-
-      global = @llvm_mod.globals.add(type, name)
-      global.linkage = LLVM::Linkage::Private
-      global.global_constant = true
-      global.initializer = llvm_type(@program.string).const_array(id_map)
-      global
+      @main_llvm_typer.llvm_type(@program.string).const_array(id_map)
     end
 
     def visit(node : IsA)
@@ -2538,22 +2549,23 @@ module Crystal
       @last = last
     end
 
-    def build_string_constant(str, name = "str")
+    def build_string_constant(str, name = "str", *, llvm_mod = @llvm_mod, llvm_typer = @llvm_typer)
       name = "#{name[0..18]}..." if name.bytesize > 18
       name = name.gsub '@', '.'
       name = "'#{name}'"
-      key = StringKey.new(@llvm_mod, str)
-      @strings[key] ||= begin
-        global = @llvm_mod.globals.add(@llvm_typer.llvm_string_type(str.bytesize), name.gsub('\\', "\\\\"))
+      key = StringKey.new(llvm_mod, str)
+      @strings.put_if_absent(key) do
+        llvm_context = llvm_mod.context
+        global = llvm_mod.globals.add(llvm_typer.llvm_string_type(str.bytesize), name.gsub('\\', "\\\\"))
         global.linkage = LLVM::Linkage::Private
         global.global_constant = true
         global.initializer = llvm_context.const_struct [
-          int32(@program.llvm_id.type_id(@program.string)), # in practice, should always be 1
-          int32(str.bytesize),
-          int32(str.size),
+          llvm_context.int32.const_int(@program.llvm_id.type_id(@program.string)), # in practice, should always be 1
+          llvm_context.int32.const_int(str.bytesize),
+          llvm_context.int32.const_int(str.size),
           llvm_context.const_string(str),
         ]
-        cast_to global, @program.string
+        pointer_cast global, llvm_typer.llvm_type(@program.string)
       end
     end