Improve COW/etc handling for update assignments

3 files changed, 35 insertions, 27 deletions

diff --git a/builtins/array.h b/builtins/array.h
index 6375f6d4..df66e636 100644
--- a/builtins/array.h
+++ b/builtins/array.h
@@ -17,14 +17,16 @@
     if (__builtin_expect($off < 0 || $off >= $arr.length, 0)) \
         fail_source(filename, start, end, "Invalid array index: %r (array has length %ld)\n", Int__as_text(&$index, USE_COLOR, NULL), $arr.length); \
     (item_type*)($arr.data + $arr.stride * $off);})
-#define $Array_set(item_type, arr_expr, index_expr, value_expr, typeinfo, filename, start, end) { \
+#define $Array_lvalue(item_type, arr_expr, index_expr, typeinfo, filename, start, end) { \
     array_t *$arr = arr_expr; int64_t $index = (int64_t)(index_expr); \
     int64_t $off = $index + ($index < 0) * ($arr->length + 1) - 1; \
     if (__builtin_expect($off < 0 || $off >= $arr->length, 0)) \
         fail_source(filename, start, end, "Invalid array index: %r (array has length %ld)\n", Int__as_text(&$index, USE_COLOR, NULL), $arr->length); \
     if ($arr->data_refcount > 0) \
         Array__compact($arr, typeinfo); \
-    *(item_type*)($arr->data + $arr->stride * $off) = value_expr; }
+    *(item_type*)($arr->data + $arr->stride * $off); }
+#define $Array_set(item_type, arr, index, value, typeinfo, filename, start, end) \
+    $Array_lvalue(item_type, arr_expr, index, typeinfo, filename, start, end) = value
 #define $Array_get_unchecked(type, x, i) *({ const array_t $arr = x; int64_t $index = (int64_t)(i); \
                                           int64_t $off = $index + ($index < 0) * ($arr.length + 1) - 1; \
                                           (type*)($arr.data + $arr.stride * $off);})
diff --git a/builtins/table.h b/builtins/table.h
index a29fa7cc..ab0004ec 100644
--- a/builtins/table.h
+++ b/builtins/table.h
@@ -48,6 +48,7 @@ void *Table_reserve(table_t *t, const void *key, const void *value, const TypeIn
 void Table_set(table_t *t, const void *key, const void *value, const TypeInfo *type);
 #define Table_set_value(t, key_expr, value_expr, type) ({ __typeof(key_expr) $k = key_expr; __typeof(value_expr) $v = value_expr; \
                                                         Table_set(t, &$k, &$v, type); })
+#define Table_reserve_value(t, key_expr, type) ({ __typeof(key_expr) $k = key_expr; Table_reserve(t, &$k, NULL, type); })
 void Table_remove(table_t *t, const void *key, const TypeInfo *type);
 void Table_clear(table_t *t);
 void Table_mark_copy_on_write(table_t *t);
diff --git a/compile.c b/compile.c
index e08a13f7..4c4b322d 100644
--- a/compile.c
+++ b/compile.c
@@ -113,7 +113,7 @@ CORD compile_type(env_t *env, type_t *t)
     }
 }
 
-static void check_assignable(env_t *env, ast_t *ast)
+static CORD compile_lvalue(env_t *env, ast_t *ast)
 {
     if (!can_be_mutated(env, ast)) {
         if (ast->tag == Index || ast->tag == FieldAccess) {
@@ -123,34 +123,41 @@ static void check_assignable(env_t *env, ast_t *ast)
             code_err(ast, "This is a value of type %T and can't be assigned to", get_type(env, ast));
         }
     }
-}
 
-static CORD compile_assignment(env_t *env, ast_t *target, CORD value)
-{
-    check_assignable(env, target);
-    if (target->tag == Index) {
-        auto index = Match(target, Index);
+    if (ast->tag == Index) {
+        auto index = Match(ast, Index);
         type_t *container_t = get_type(env, index->indexed);
+        if (!index->index && container_t->tag == PointerType) {
+            if (Match(container_t, PointerType)->is_optional)
+                code_err(index->indexed, "This pointer might be null, so it can't be safely assigned to");
+            return compile(env, ast);
+        }
         container_t = value_type(container_t);
-        switch (container_t->tag) {
-        case ArrayType: {
+        if (container_t->tag == ArrayType) {
             CORD target_code = compile_to_pointer_depth(env, index->indexed, 1, false);
             type_t *item_type = Match(container_t, ArrayType)->item_type;
-            return CORD_all("$Array_set(", compile_type(env, item_type), ", ", target_code, ", ", 
-                            compile(env, index->index), ", ", value, ", ", compile_type_info(env, container_t),
-                            ", ", Text__quoted(target->file->filename, false), ", ", heap_strf("%ld", target->start - target->file->text),
-                            ", ", heap_strf("%ld", target->end - target->file->text), ");\n");
-        }
-        case TableType: {
+            return CORD_all("$Array_lvalue(", compile_type(env, item_type), ", ", target_code, ", ", 
+                            compile(env, index->index), ", ", compile_type_info(env, container_t),
+                            ", ", Text__quoted(ast->file->filename, false), ", ", heap_strf("%ld", ast->start - ast->file->text),
+                            ", ", heap_strf("%ld", ast->end - ast->file->text), ")");
+        } else if (container_t->tag == TableType) {
             CORD target_code = compile_to_pointer_depth(env, index->indexed, 1, false);
-            return CORD_all("Table_set_value(", target_code, ", ", compile(env, index->index), ", ",
-                            value, ", ", compile_type_info(env, container_t), ");\n");
-        }
-        case PointerType: break;
-        default: code_err(target, "I don't know how to assign to this target");
+            type_t *value_t = Match(container_t, TableType)->value_type;
+            return CORD_all("*(", compile_type(env, value_t), "*)Table_reserve_value(", target_code, ", ",
+                            compile(env, index->index),", ", compile_type_info(env, container_t), ")");
+        } else {
+            code_err(ast, "I don't know how to assign to this target");
         }
+    } else if (ast->tag == Var || ast->tag == FieldAccess) {
+        return compile(env, ast);
+    } else {
+        code_err(ast, "I don't know how to assign to this");
     }
-    return CORD_all(compile(env, target), " = ", value, ";\n");
+}
+
+static CORD compile_assignment(env_t *env, ast_t *target, CORD value)
+{
+    return CORD_all(compile_lvalue(env, target), " = ", value, ";\n");
 }
 
 CORD compile_statement(env_t *env, ast_t *ast)
@@ -222,7 +229,6 @@ CORD compile_statement(env_t *env, ast_t *ast)
             auto assign = Match(test->expr, Assign);
             if (!assign->targets->next && assign->targets->ast->tag == Var) {
                 // Common case: assigning to one variable:
-                check_assignable(env, assign->targets->ast);
                 CORD var = compile(env, assign->targets->ast);
                 CORD code = compile_assignment(env, assign->targets->ast, compile(env, assign->values->ast));
                 CORD_appendf(&code, "$test(&%r, %r, %r, %r, %ld, %ld);",
@@ -315,8 +321,7 @@ CORD compile_statement(env_t *env, ast_t *ast)
     }
     case UpdateAssign: {
         auto update = Match(ast, UpdateAssign);
-        check_assignable(env, update->lhs);
-        CORD lhs = compile(env, update->lhs);
+        CORD lhs = compile_lvalue(env, update->lhs);
         CORD rhs = compile(env, update->rhs);
 
         type_t *lhs_t = get_type(env, update->lhs);
@@ -330,7 +335,7 @@ CORD compile_statement(env_t *env, ast_t *ast)
             operand_t = lhs_t;
         else
             code_err(ast, "I can't do operations between %T and %T", lhs_t, rhs_t);
-
+        
         switch (update->op) {
         case BINOP_MULT: return CORD_asprintf("%r *= %r;", lhs, rhs);
         case BINOP_DIVIDE: return CORD_asprintf("%r /= %r;", lhs, rhs);