all: implement reference receiver optimization for big structs (#9268)

vlib/v/ast/str.v

@@ -33,6 +33,9 @@ pub fn (node &FnDecl) stringify(t &table.Table, cur_mod string, m2a map[string]s
 			styp = styp[1..] // remove &
 		}
 		styp = util.no_cur_mod(styp, cur_mod)
+		if node.params[0].is_auto_rec {
+			styp = styp.trim('&')
+		}
 		receiver = '($m$node.receiver.name $styp) '
 		/*
 		sym := t.get_type_symbol(node.receiver.typ)

vlib/v/checker/checker.v

@@ -2444,6 +2444,9 @@ pub fn (mut c Checker) return_stmt(mut return_stmt ast.Return) {
 			got_typ_sym := c.table.get_type_symbol(got_typ)
 			mut exp_typ_sym := c.table.get_type_symbol(exp_type)
 			pos := return_stmt.exprs[i].position()
+			if return_stmt.exprs[i].is_auto_deref_var() {
+				continue
+			}
 			if exp_typ_sym.kind == .interface_ {
 				c.type_implements(got_typ, exp_type, return_stmt.pos)
 				continue
@@ -2454,12 +2457,18 @@ pub fn (mut c Checker) return_stmt(mut return_stmt ast.Return) {
 		if (got_typ.is_ptr() || got_typ.is_pointer())
 			&& (!exp_type.is_ptr() && !exp_type.is_pointer()) {
 			pos := return_stmt.exprs[i].position()
+			if return_stmt.exprs[i].is_auto_deref_var() {
+				continue
+			}
 			c.error('fn `$c.cur_fn.name` expects you to return a non reference type `${c.table.type_to_str(exp_type)}`, but you are returning `${c.table.type_to_str(got_typ)}` instead',
 				pos)
 		}
 		if (exp_type.is_ptr() || exp_type.is_pointer())
 			&& (!got_typ.is_ptr() && !got_typ.is_pointer()) && got_typ != table.int_literal_type {
 			pos := return_stmt.exprs[i].position()
+			if return_stmt.exprs[i].is_auto_deref_var() {
+				continue
+			}
 			c.error('fn `$c.cur_fn.name` expects you to return a reference type `${c.table.type_to_str(exp_type)}`, but you are returning `${c.table.type_to_str(got_typ)}` instead',
 				pos)
 		}
@@ -4713,7 +4722,7 @@ fn (mut c Checker) match_exprs(mut node ast.MatchExpr, cond_type_sym table.TypeS
 }
 
 // smartcast takes the expression with the current type which should be smartcasted to the target type in the given scope
-fn (c Checker) smartcast_sumtype(expr ast.Expr, cur_type table.Type, to_type table.Type, mut scope ast.Scope) {
+fn (c &Checker) smartcast_sumtype(expr ast.Expr, cur_type table.Type, to_type table.Type, mut scope ast.Scope) {
 	match mut expr {
 		ast.SelectorExpr {
 			mut is_mut := false
@@ -5684,7 +5693,7 @@ pub fn (mut c Checker) error(message string, pos token.Position) {
 }
 
 // check `to` has all fields of `from`
-fn (c Checker) check_struct_signature(from table.Struct, to table.Struct) bool {
+fn (c &Checker) check_struct_signature(from table.Struct, to table.Struct) bool {
 	// Note: `to` can have extra fields
 	if from.fields.len == 0 {
 		return false

vlib/v/gen/c/cgen.v

@@ -4496,7 +4496,18 @@ fn (mut g Gen) return_statement(node ast.Return) {
 		} else {
 			g.write('return ')
 		}
+		if expr0.is_auto_deref_var() {
+			if g.fn_decl.return_type.is_ptr() {
+				g.write('&(*')
+				g.expr(expr0)
+				g.write(')')
+			} else {
+				g.write('*')
+				g.expr(expr0)
+			}
+		} else {
 			g.expr_with_cast(node.exprs[0], node.types[0], g.fn_decl.return_type)
+		}
 		if free {
 			expr := node.exprs[0]
 			if expr is ast.Ident {

vlib/v/parser/fn.v

@@ -279,7 +279,7 @@ fn (mut p Parser) fn_decl() ast.FnDecl {
 				name: param.name
 				typ: param.typ
 				is_mut: param.is_mut
-				is_auto_deref: param.is_mut
+				is_auto_deref: param.is_mut || param.is_auto_rec
 				pos: param.pos
 				is_used: true
 				is_arg: true
@@ -478,10 +478,22 @@ fn (mut p Parser) fn_receiver(mut params []table.Param, mut rec ReceiverParsingI
 	if is_atomic {
 		rec.typ = rec.typ.set_flag(.atomic_f)
 	}
+	// optimize method `automatic use fn (a &big_foo) instead of fn (a big_foo)`
+	type_sym := p.table.get_type_symbol(rec.typ)
+	mut is_auto_rec := false
+	if type_sym.kind == .struct_ {
+		info := type_sym.info as table.Struct
+		if !rec.is_mut && !rec.typ.is_ptr() && info.fields.len > 8 {
+			rec.typ = rec.typ.to_ptr()
+			is_auto_rec = true
+		}
+	}
+
 	params << table.Param{
 		pos: rec_start_pos
 		name: rec.name
 		is_mut: rec.is_mut
+		is_auto_rec: is_auto_rec
 		typ: rec.typ
 	}
 	p.check(.rpar)

vlib/v/table/table.v

@@ -60,6 +60,7 @@ pub:
 	pos         token.Position
 	name        string
 	is_mut      bool
+	is_auto_rec bool
 	typ         Type
 	type_pos    token.Position
 	is_hidden   bool // interface first arg