diff --git a/vlib/os/file.v b/vlib/os/file.v
index ed3a08c94d..45b824c95e 100644
--- a/vlib/os/file.v
+++ b/vlib/os/file.v
@@ -86,7 +86,7 @@ pub fn (f &File) read_bytes(size int) []byte {
 // read_bytes_at reads bytes at the given position in the file
 pub fn (f &File) read_bytes_at(size, pos int) []byte {
 	mut arr := []byte{len: size}
-	nreadbytes := f.read_bytes_into(pos, arr) or {
+	nreadbytes := f.read_bytes_into(pos, mut arr) or {
 		// return err
 		return []
 	}
diff --git a/vlib/v/ast/ast.v b/vlib/v/ast/ast.v
index 82ea0ec0af..5e6748a8f6 100644
--- a/vlib/v/ast/ast.v
+++ b/vlib/v/ast/ast.v
@@ -286,6 +286,7 @@ pub mut:
 	return_type        table.Type
 	should_be_skipped  bool
 	generic_type       table.Type // TODO array, to support multiple types
+	autofree_pregen    string
 	// autofree_vars      []AutofreeArgVar
 	// autofree_vars_ids  []int
 }
diff --git a/vlib/v/checker/checker.v b/vlib/v/checker/checker.v
index c076e75df6..e35e68dcef 100644
--- a/vlib/v/checker/checker.v
+++ b/vlib/v/checker/checker.v
@@ -934,7 +934,30 @@ fn (mut c Checker) fail_if_immutable(expr ast.Expr) (string, token.Position) {
 
 pub fn (mut c Checker) call_expr(mut call_expr ast.CallExpr) table.Type {
 	c.stmts(call_expr.or_block.stmts)
-	typ := if call_expr.is_method { c.call_method(call_expr) } else { c.call_fn(call_expr) }
+	// First check everything that applies to both fns and methods
+	// TODO merge logic from call_method and call_fn
+	/*
+	for i, call_arg in call_expr.args {
+		if call_arg.is_mut {
+			c.fail_if_immutable(call_arg.expr)
+			if !arg.is_mut {
+				tok := call_arg.share.str()
+				c.error('`$call_expr.name` parameter `$arg.name` is not `$tok`, `$tok` is not needed`',
+					call_arg.expr.position())
+			} else if arg.typ.share() != call_arg.share {
+				c.error('wrong shared type', call_arg.expr.position())
+			}
+		} else {
+			if arg.is_mut && (!call_arg.is_mut || arg.typ.share() != call_arg.share) {
+				tok := call_arg.share.str()
+				c.error('`$call_expr.name` parameter `$arg.name` is `$tok`, you need to provide `$tok` e.g. `$tok arg${i+1}`',
+					call_arg.expr.position())
+			}
+		}
+	}
+	*/
+	// Now call `call_method` or `call_fn` for specific checks.
+	typ := if call_expr.is_method { c.call_method(mut call_expr) } else { c.call_fn(mut call_expr) }
 	// autofree
 	free_tmp_arg_vars := c.pref.autofree && c.pref.experimental && !c.is_builtin_mod &&
 		call_expr.args.len > 0 && !call_expr.args[0].typ.has_flag(.optional)
@@ -1153,6 +1176,24 @@ pub fn (mut c Checker) call_method(mut call_expr ast.CallExpr) table.Type {
 						call_expr.pos)
 				}
 			}
+			param := if method.is_variadic && i >= method.args.len - 1 { method.args[method.args.len -
+					1] } else { method.args[i + 1] }
+			if arg.is_mut {
+				c.fail_if_immutable(arg.expr)
+				if !param.is_mut {
+					tok := arg.share.str()
+					c.error('`$call_expr.name` parameter `$param.name` is not `$tok`, `$tok` is not needed`',
+						arg.expr.position())
+				} else if param.typ.share() != arg.share {
+					c.error('wrong shared type', arg.expr.position())
+				}
+			} else {
+				if param.is_mut && (!arg.is_mut || param.typ.share() != arg.share) {
+					tok := arg.share.str()
+					c.error('`$call_expr.name` parameter `$param.name` is `$tok`, you need to provide `$tok` e.g. `$tok arg${i+1}`',
+						arg.expr.position())
+				}
+			}
 		}
 		if method.is_unsafe && !c.inside_unsafe {
 			c.warn('method `${left_type_sym.source_name}.$method_name` must be called from an `unsafe` block',
@@ -2339,7 +2380,7 @@ fn (mut c Checker) stmt(node ast.Stmt) {
 		ast.GotoLabel {}
 		ast.GotoStmt {}
 		ast.HashStmt {
-			c.hash_stmt(node)
+			c.hash_stmt(mut node)
 		}
 		ast.Import {
 			c.import_stmt(node)
@@ -2358,7 +2399,7 @@ fn (mut c Checker) stmt(node ast.Stmt) {
 			c.scope_returns = true
 		}
 		ast.SqlStmt {
-			c.sql_stmt(node)
+			c.sql_stmt(mut node)
 		}
 		ast.StructDecl {
 			c.struct_decl(node)
@@ -2663,7 +2704,7 @@ pub fn (mut c Checker) expr(node ast.Expr) table.Type {
 			return c.match_expr(mut node)
 		}
 		ast.PostfixExpr {
-			return c.postfix_expr(node)
+			return c.postfix_expr(mut node)
 		}
 		ast.PrefixExpr {
 			right_type := c.expr(node.right)
@@ -2731,7 +2772,7 @@ pub fn (mut c Checker) expr(node ast.Expr) table.Type {
 			return table.u32_type
 		}
 		ast.SqlExpr {
-			return c.sql_expr(node)
+			return c.sql_expr(mut node)
 		}
 		ast.StringLiteral {
 			if node.language == .c {
@@ -2906,7 +2947,7 @@ pub fn (mut c Checker) ident(mut ident ast.Ident) table.Type {
 		// main.compare_f32 may actually be builtin.compare_f32
 		saved_mod := ident.mod
 		ident.mod = 'builtin'
-		builtin_type := c.ident(ident)
+		builtin_type := c.ident(mut ident)
 		if builtin_type != table.void_type {
 			return builtin_type
 		}
@@ -3182,8 +3223,9 @@ pub fn (mut c Checker) select_expr(mut node ast.SelectExpr) table.Type {
 }
 
 pub fn (mut c Checker) lock_expr(mut node ast.LockExpr) table.Type {
-	for id in node.lockeds {
-		c.ident(mut id)
+	for i, id in node.lockeds {
+		// c.ident(mut id)
+		c.ident(mut node.lockeds[i])
 		if id.obj is ast.Var as v {
 			if v.typ.share() != .shared_t {
 				c.error('`$id.name` must be declared `shared` to be locked', id.pos)
diff --git a/vlib/v/gen/cgen.v b/vlib/v/gen/cgen.v
index e7b0a01d47..c19fe1b3d1 100644
--- a/vlib/v/gen/cgen.v
+++ b/vlib/v/gen/cgen.v
@@ -101,6 +101,7 @@ mut:
 	inside_return         bool
 	inside_or_block       bool
 	strs_to_free          []string // strings.Builder
+	strs_to_free0         []string // strings.Builder
 	inside_call           bool
 	has_main              bool
 	inside_const          bool
@@ -1915,7 +1916,21 @@ fn (mut g Gen) expr(node ast.Expr) {
 			g.write(node.val.str())
 		}
 		ast.CallExpr {
+			// if g.fileis('1.strings') {
+			// println('\ncall_expr()()')
+			// }
 			g.call_expr(node)
+			// if g.fileis('1.strings') {
+			// println('before:' + node.autofree_pregen)
+			// }
+			if g.pref.autofree && node.autofree_pregen != '' { // g.strs_to_free0.len != 0 {
+				// g.insert_before_stmt('/*START2*/' + g.strs_to_free0.join('\n') + '/*END*/')
+				g.insert_before_stmt('/*START3*/' + node.autofree_pregen + '/*END*/')
+				// for s in g.strs_to_free0 {
+				// //g.writeln(s)
+				// }
+				g.strs_to_free0 = []
+			}
 		}
 		ast.CastExpr {
 			// g.write('/*cast*/')
diff --git a/vlib/v/gen/fn.v b/vlib/v/gen/fn.v
index 8b947bb8a2..294ee61746 100644
--- a/vlib/v/gen/fn.v
+++ b/vlib/v/gen/fn.v
@@ -419,7 +419,9 @@ fn (mut g Gen) method_call(node ast.CallExpr) {
 			}
 		}
 	}
-	g.generate_tmp_autofree_arg_vars(node, name)
+	// TODO2
+	// g.generate_tmp_autofree_arg_vars(mut node, name)
+	//
 	// if node.receiver_type != 0 {
 	// g.write('/*${g.typ(node.receiver_type)}*/')
 	// g.write('/*expr_type=${g.typ(node.left_type)} rec type=${g.typ(node.receiver_type)}*/')
@@ -534,7 +536,8 @@ fn (mut g Gen) fn_call(node ast.CallExpr) {
 		// `foo<int>()` => `foo_int()`
 		name += '_' + g.typ(node.generic_type)
 	}
-	g.generate_tmp_autofree_arg_vars(node, name)
+	// TODO2
+	// g.generate_tmp_autofree_arg_vars(node, name)
 	// Handle `print(x)`
 	if is_print && node.args[0].typ != table.string_type { // && !free_tmp_arg_vars {
 		typ := node.args[0].typ
@@ -614,7 +617,10 @@ fn (mut g Gen) fn_call(node ast.CallExpr) {
 	g.is_json_fn = false
 }
 
-fn (mut g Gen) generate_tmp_autofree_arg_vars(node ast.CallExpr, name string) {
+fn (mut g Gen) generate_tmp_autofree_arg_vars(mut node ast.CallExpr, name string) {
+	// if g.fileis('1.strings') {
+	// println('gen tmp autofree()')
+	// }
 	// Create a temporary var before fn call for each argument in order to free it (only if it's a complex expression,
 	// like `foo(get_string())` or `foo(a + b)`
 	mut free_tmp_arg_vars := g.autofree && g.pref.experimental && !g.is_builtin_mod &&
@@ -633,7 +639,10 @@ fn (mut g Gen) generate_tmp_autofree_arg_vars(node ast.CallExpr, name string) {
 			t := '_tt${g.tmp_count2}_arg_expr_${fn_name}_$i'
 			g.called_fn_name = name
 			str_expr := g.write_expr_to_string(arg.expr)
-			g.insert_before_stmt('string $t = $str_expr; // new4. to free arg #$i name=$name')
+			// g.insert_before_stmt('string $t = $str_expr; // new4. to free arg #$i name=$name')
+			// g.strs_to_free0 << 'string $t = $str_expr; // new5. to free arg #$i name=$name'
+			node.autofree_pregen += 'string $t = $str_expr; // new6. to free arg #$i name=$name\n'
+			// println('setting pregen to ' + node.autofree_pregen)
 			// cur_line = g.go_before_stmt(0)
 			// println('cur line ="$cur_line"')
 			// g.writeln('string $t = $str_expr; // new3. to free arg #$i name=$name')
diff --git a/vlib/v/parser/parser.v b/vlib/v/parser/parser.v
index eed05f7782..d158af3434 100644
--- a/vlib/v/parser/parser.v
+++ b/vlib/v/parser/parser.v
@@ -1501,13 +1501,13 @@ fn (mut p Parser) import_stmt() ast.Import {
 			p.error_with_pos('import alias `$mod_name as $mod_alias` is redundant', p.prev_tok.position())
 		}
 	}
-	node := ast.Import{
+	mut node := ast.Import{
 		pos: pos
 		mod: mod_name
 		alias: mod_alias
 	}
 	if p.tok.kind == .lcbr { // import module { fn1, Type2 } syntax
-		p.import_syms(node)
+		p.import_syms(mut node)
 		p.register_used_import(mod_name) // no `unused import` msg for parent
 	}
 	pos_t := p.tok.position()
diff --git a/vlib/v/tests/valgrind/1.strings_and_arrays.v b/vlib/v/tests/valgrind/1.strings_and_arrays.v
index 9f7cc02b25..7d6e0998d2 100644
--- a/vlib/v/tests/valgrind/1.strings_and_arrays.v
+++ b/vlib/v/tests/valgrind/1.strings_and_arrays.v
@@ -34,6 +34,13 @@ fn str_tmp_expr() {
 }
 
 fn str_tmp_expr_advanced() {
+	// t1 = 'c' + 'd'
+	// t2 = 'e + f'
+	// t3 = add_strings(t2, 'g')
+	// handle_strings(t1, t3)
+	// t1.free()
+	// t2.free()
+	// t3.free()
 	// handle_strings('c' + 'd', add_strings('e' + 'f', 'g')) // both lvl 1 and lvl2 exprs must be freed
 }
 
@@ -112,3 +119,11 @@ fn main() {
 	// str_replace()
 	println('end')
 }
+
+/*
+s := s.replace().replace()
+tmp := s.replace()
+s.free()
+s = tmp.replace()
+tmp.free()
+*/