Global variables now supported! + some fixes to OP_ASSIGN

Previously we weren't creating a new assignment node, and this was
causing all sorts of funky errors. This commit also fixes that, and
we can now use global variables :^)

4 files changed, 93 insertions, 42 deletions

diff --git a/src/ast.c b/src/ast.c
index 6e33de1..ebecf54 100644
--- a/src/ast.c
+++ b/src/ast.c
@@ -109,7 +109,7 @@ static void do_print_ast(Node *node, int depth)
         printf("%s\n", node_type_to_str(node->type));
         do_print_ast(node->binary.left, depth + 1);
         do_print_ast(node->binary.right, depth + 1);
-    } else if (node->type == AST_VAR) {
+    } else if (node->type == AST_LOCAL_VAR) {
         assert(node->variable && node->variable->name);
         printf("%s\n", node->variable->name);
     } else if (node->type == AST_VARDECL) {
diff --git a/src/ast.h b/src/ast.h
index 0413f79..39d1a4e 100644
--- a/src/ast.h
+++ b/src/ast.h
@@ -30,7 +30,8 @@
   F(AST_WHILE, "while statement")                                              \
   F(AST_FOR, "for statement")                                                  \
   F(AST_VARDECL, "variable decl")                                              \
-  F(AST_VAR, "variable")                                                       \
+  F(AST_LOCAL_VAR, "local variable")                                           \
+  F(AST_GLOBAL_VAR, "global variable")                                         \
   F(AST_RETURN, "return")                                                      \
   F(AST_FUNC, "func")                                                          \
   F(AST_BUILTIN, "builtin")                                                    \
@@ -120,7 +121,7 @@ typedef struct ast_node {
         } var_decl;
 
         struct {
-            Variable *var;
+            Node *var;
             Node *value;
         } assign;
 
diff --git a/src/generator.c b/src/generator.c
index b141dce..c7a50bc 100644
--- a/src/generator.c
+++ b/src/generator.c
@@ -51,17 +51,33 @@ void generate_expr_into_rax(Node *expr, FILE *out)
     } else if (expr->type == AST_FUNCCALL) {
         generate_func_call(expr, out);
 
-    } else if (expr->type == AST_VAR) {
+    } else if (expr->type == AST_LOCAL_VAR) {
         i64 offset = expr->variable->offset;
         if (offset > 0)
             fprintf(out, "    mov rax, [rbp-%lld]\n", offset);
         else
             fprintf(out, "    mov rax, [rbp+%lld]\n", -offset);
 
+    } else if (expr->type == AST_GLOBAL_VAR) {
+        i64 offset = expr->variable->offset;
+        fprintf(out, "    mov rax, global_vars\n");
+        fprintf(out, "    add rax, %lld\n", offset);
+        fprintf(out, "    mov rax, [rax]\n");
+
     } else if (expr->type == OP_ASSIGN) {
-        i64 offset = expr->assign.var->offset;
+        Node *var = expr->assign.var;
+        i64 offset = var->variable->offset;
         generate_expr_into_rax(expr->assign.value, out);
-        fprintf(out, "    mov [rbp-%lld], rax\n", offset);
+
+        if (var->type == AST_LOCAL_VAR) {
+            fprintf(out, "    mov [rbp-%lld], rax\n", offset);
+        } else if (var->type == AST_GLOBAL_VAR) {
+            fprintf(out, "    mov rbx, global_vars\n");
+            fprintf(out, "    mov [rbx+%lld], rax\n", offset);
+        } else {
+            fprintf(stderr, "Unhandled assignment type: %s\n", node_type_to_str(var->type));
+            exit(1);
+        }
 
     } else if (expr->type == OP_NEG) {
         generate_expr_into_rax(expr->unary_expr, out);
@@ -342,10 +358,13 @@ void generate_asm(Node *root, FILE *out)
 {
     assert(root->type == AST_PROGRAM);
     for (int i = 0; i < root->block.num_children; i++) {
-        if (root->block.children[i]->type == AST_FUNC) {
-            generate_function(root->block.children[i], out);
+        Node *child = root->block.children[i];
+        if (child->type == AST_FUNC) {
+            generate_function(child, out);
+        } else if (child->type == AST_VARDECL) {
+            // Do nothing, we don't need to generate global variables
         } else {
-            fprintf(stderr, "Unsupported node type in generate_asm: %s\n", node_type_to_str(root->block.children[i]->type));
+            fprintf(stderr, "Unsupported node type in generate_asm: %s\n", node_type_to_str(child->type));
             exit(1);
         }
     }
@@ -363,8 +382,12 @@ void generate_asm(Node *root, FILE *out)
     fprintf(out, "    mov rdi, rax\n");
     make_syscall(SYS_exit, out);
 
+    // TODO: Don't generate code for functions that cannot get called.
     // TODO: Add implementations of some primitives?
     generate_builtins(out);
+
+    fprintf(out, "section .bss\n");
+    fprintf(out, "    global_vars: resb %lld\n", root->block.locals_size);
 }
 
 void generate_builtins(FILE *out)
@@ -379,14 +402,6 @@ void generate_builtins(FILE *out)
         "    mov BYTE [rsp+31], 10\n"
         "    lea rcx, [rsp+30]\n"
         "    mov qword rbx, 0\n"
-
-        // Check if < 0, and set rbx=0, negate value
-        // "    cmp rdi, 0\n"
-        // "    jge .L2\n"
-        // "    mov qword rbx, 1\n"
-        // "    neg rdi\n"
-        // "    sub rcx, 1\n"
-
         ".L2:\n"
         "    mov rax, rdi\n"
         "    lea r8, [rsp+32]\n"
@@ -405,19 +420,6 @@ void generate_builtins(FILE *out)
         "    sub rcx, 1\n"
         "    cmp rax, 9\n"
         "    ja .L2\n"
-
-        // If rbx=1, then we need to add a minus sign, not sure how
-        // the above code works so there's probably a nicer way.
-        // "    cmp rbx, 0\n"
-        // "    je .end_neg_sign\n"
-        // "    add eax, 48\n"
-        // "    mov BYTE [rcx], 45\n"
-        // "    mov rax, rdi\n"
-        // "    mov rdi, rdx\n"
-        // "    mov rdx, rcx\n"
-        // "    sub rcx, 1\n"
-        // ".end_neg_sign:\n"
-
         "    lea rax, [rsp+32]\n"
         "    mov edi, 1\n"
         "    sub rdx, rax\n"
diff --git a/src/parser.c b/src/parser.c
index 4dc891d..a0ec7a1 100644
--- a/src/parser.c
+++ b/src/parser.c
@@ -15,11 +15,16 @@ static Node *block_stack[BLOCK_STACK_SIZE];
 static i64 block_stack_count = 0;
 static i64 cur_stack_offset = 0;
 
+// TODO: Probably use a vector here
+#define GLOBAL_VARS_SIZE 1024
+static Variable *global_vars[GLOBAL_VARS_SIZE];
+static i64 global_vars_count = 0;
+static i64 global_vars_offset = 0;
+
 #define LEXER_STACK_SIZE 64
 static Lexer *lexer_stack[LEXER_STACK_SIZE];
 static i64 lexer_stack_count = 0;
 
-
 Token do_assert_token(Token token, TokenType type, char *filename, int line)
 {
     if (token.type != type) {
@@ -133,6 +138,9 @@ Node *find_builtin_function(Token *token)
 
 Variable *find_local_variable(Token *token)
 {
+    if (current_function == NULL)
+        return NULL;
+
     assert_token(*token, TOKEN_IDENTIFIER);
     for (i64 i = block_stack_count - 1; i >= 0; --i) {
         Node *block = block_stack[i];
@@ -151,6 +159,16 @@ Variable *find_local_variable(Token *token)
     return NULL;
 }
 
+Variable *find_global_variable(Token *token)
+{
+    for (int i = 0; i < global_vars_count; i++) {
+        if (strcmp(global_vars[i]->name, token->value.as_string) == 0) {
+            return global_vars[i];
+        }
+    }
+    return NULL;
+}
+
 Node *find_function_definition(Token *token)
 {
     assert_token(*token, TOKEN_IDENTIFIER);
@@ -163,6 +181,15 @@ Node *find_function_definition(Token *token)
     return NULL;
 }
 
+void add_global_variable(Variable *var)
+{
+    var->offset = global_vars_offset;
+    // TODO: Compute based on type
+    int var_size = 8;
+    global_vars_offset += var_size;
+    global_vars[global_vars_count++] = var;
+}
+
 // TODO: rename this, it's ugly
 void add_variable_to_current_block(Variable *var)
 {
@@ -224,16 +251,16 @@ Node *parse_expression(Lexer *);
 
 Node *parse_var_declaration(Lexer *lexer)
 {
+    bool is_global = (current_function == NULL);
     Token token = assert_token(Lexer_next(lexer), TOKEN_LET);
-    // TODO: Reuse this for globals? Or maybe just make a new function?
-    if (!current_function || current_function->type != AST_FUNC)
-        die_location(token.loc, "Variable declaration outside of function");
 
     token = assert_token(Lexer_next(lexer), TOKEN_IDENTIFIER);
     // NOTE: We don't allow shadowing of variables in the any blocks,
     //       this is by design since it's a common mistake.
     if (find_local_variable(&token) != NULL)
-        die_location(token.loc, "Variable `%s` already declared", token.value.as_string);
+        die_location(token.loc, "Variable `%s` already declared in function", token.value.as_string);
+    if (find_global_variable(&token) != NULL)
+        die_location(token.loc, "Variable `%s` already declared globally", token.value.as_string);
 
     Node *node = Node_new(AST_VARDECL);
     node->var_decl.var.name = token.value.as_string;
@@ -243,10 +270,16 @@ Node *parse_var_declaration(Lexer *lexer)
         die_location(token.loc, "Missing type specifier for variable `%s`", node->var_decl.var.name);
     node->var_decl.var.type = parse_type(lexer);
 
-    add_variable_to_current_block(&node->var_decl.var);
+    if (is_global) {
+        add_global_variable(&node->var_decl.var);
+    } else {
+        add_variable_to_current_block(&node->var_decl.var);
+    }
 
     token = Lexer_next(lexer);
     if (token.type == TOKEN_ASSIGN) {
+        if (is_global)
+            die_location(token.loc, "Cannot initialize global variable `%s` outside function", node->var_decl.var.name);
         node->var_decl.value = parse_expression(lexer);
         assert_token(Lexer_next(lexer), TOKEN_SEMICOLON);
     } else {
@@ -317,11 +350,19 @@ Node *parse_factor(Lexer *lexer)
         Variable *var = find_local_variable(&token);
         if (var != NULL) {
             Lexer_next(lexer);
-            expr = Node_new(AST_VAR);
+            expr = Node_new(AST_LOCAL_VAR);
             expr->variable = var;
             return expr;
         }
 
+        Variable *gvar = find_global_variable(&token);
+        if (gvar != NULL) {
+            Lexer_next(lexer);
+            expr = Node_new(AST_GLOBAL_VAR);
+            expr->variable = gvar;
+            return expr;
+        }
+
         Node *func = find_function_definition(&token);
         if (func != NULL) {
             return parse_function_call_args(lexer, func);
@@ -396,14 +437,14 @@ Node *parse_expression(Lexer *lexer)
     Node *node = parse_conditional_exp(lexer);
     // FIXME: This is a hack to handle assignment expressions
     //        and can probably be done properly.
-    if (node->type == AST_VAR) {
+    if (node->type == AST_LOCAL_VAR || node->type == AST_GLOBAL_VAR) {
         Token token = Lexer_peek(lexer);
         if (token.type == TOKEN_ASSIGN) {
             Lexer_next(lexer);
-            Variable *var = node->variable;
-            node->type = OP_ASSIGN;
-            node->assign.var = var;
-            node->assign.value = parse_expression(lexer);
+            Node *assign = Node_new(OP_ASSIGN);
+            assign->assign.var = node;
+            assign->assign.value = parse_expression(lexer);
+            node = assign;
         }
     }
     return node;
@@ -577,6 +618,9 @@ Node *parse_func(Lexer *lexer)
     assert(block_stack_count == 0);
     assert(cur_stack_offset == 0);
 
+    // Reset current function
+    current_function = NULL;
+
     return func;
 }
 
@@ -607,6 +651,9 @@ Node *parse_program(Lexer *lexer)
         if (token.type == TOKEN_FN) {
             Node *func = parse_func(lexer);
             Node_add_child(program, func);
+        } else if (token.type == TOKEN_LET) {
+            Node *var_decl = parse_var_declaration(lexer);
+            Node_add_child(program, var_decl);
         } else if (token.type == TOKEN_IMPORT) {
             // TODO: Handle circular imports
             // TODO: Handle complex import graphs (#pragma once)
@@ -629,5 +676,6 @@ Node *parse_program(Lexer *lexer)
             token = Lexer_peek(lexer);
         }
     }
+    program->block.locals_size = global_vars_offset;
     return program;
 }
\ No newline at end of file