restricted c header imports

compiler/llvm/llvm.odin

@@ -112,7 +112,7 @@ valid_value :: proc(
 	switch instructions[value_id].op {
 	case .Param, .Const, .String, .Aggregate, .None, .Optional_Some,
 	     .Load_Global, .Address_Of, .Load, .Slice, .Length, .Slice_Ptr, .Unwrap, .Orelse,
-	     .Widen, .Neg_Checked, .Add_Checked, .Pointer_Add, .Call:
+	     .Widen, .Weaken_Pointer, .Neg_Checked, .Add_Checked, .Pointer_Add, .Call:
 		return true
 	case .Address_Global, .Alloca, .Index_Address, .Field_Address, .Orelse_Begin,
 	     .Store, .Trap, .Return, .Return_Void:
@@ -707,6 +707,13 @@ emit_instruction_stream :: proc(
 			fmt.sbprintf(&emitter.builder, "  %%v%d = %s %s ", instruction_index, operation, llvm_type(from_type, &emitter.module.types))
 			write_operand(&emitter.builder, instructions, instruction.a, from_type, &emitter.module.types)
 			fmt.sbprintf(&emitter.builder, " to %s\n", llvm_type(instruction.type, &emitter.module.types))
+		case .Weaken_Pointer:
+			if !valid_instruction(instructions, instruction.a) ||
+			   !types.can_weaken_pointer(instructions[instruction.a].type, instruction.type, &emitter.module.types) {
+				emit_recovery_value(emitter, instruction_index, instruction, "invalid pointer weakening operand")
+				continue
+			}
+			fmt.sbprintf(&emitter.builder, "  %%v%d = select i1 true, ptr %%v%d, ptr null\n", instruction_index, instruction.a)
 		case .Neg_Checked:
 			if !valid_value(instructions, instruction.a, instruction.type, &emitter.module.types) {
 				emit_recovery_value(emitter, instruction_index, instruction, "invalid negation operand")
@@ -985,7 +992,19 @@ emit_constructor :: proc(emitter: ^Emitter) {
 }
 
 emit_functions :: proc(emitter: ^Emitter) {
-	for function in emitter.module.functions {
+	for function, function_index in emitter.module.functions {
+		if function.implementation == .Declaration {
+			duplicate := false
+			for previous in emitter.module.functions[:function_index] {
+				if previous.link_name == function.link_name {
+					duplicate = true
+					break
+				}
+			}
+			if duplicate {
+				continue
+			}
+		}
 		if function.implementation == .Declaration {
 			strings.write_string(&emitter.builder, "declare ")
 		} else {