all: automatically move (some) referenced objects to heap (#9873)

examples/sokol/02_cubes_glsl/cube_glsl.v

@@ -400,7 +400,7 @@ fn draw_cube_glsl(app App) {
 		0 /* padding 4 Bytes == 1 f32 */,
 	]!
 	fs_uniforms_range := C.sg_range{
-		ptr: &text_res
+		ptr: unsafe { &text_res }
 		size: size_t(4 * 4)
 	}
 	gfx.apply_uniforms(C.SG_SHADERSTAGE_FS, C.SLOT_fs_params, &fs_uniforms_range)

examples/sokol/03_march_tracing_glsl/rt_glsl.v

@@ -302,7 +302,7 @@ fn draw_cube_glsl(app App) {
 		0 // padding bytes , see "fs_params" struct paddings in rt_glsl.h
 	]!
 	fs_uniforms_range := C.sg_range{
-		ptr: &tmp_fs_params
+		ptr: unsafe { &tmp_fs_params }
 		size: size_t(sizeof(tmp_fs_params))
 	}
 	gfx.apply_uniforms(C.SG_SHADERSTAGE_FS, C.SLOT_fs_params, &fs_uniforms_range)

examples/sokol/04_multi_shader_glsl/rt_glsl.v

@@ -417,7 +417,7 @@ fn draw_cube_glsl_m(app App) {
 		0 // padding bytes , see "fs_params" struct paddings in rt_glsl.h
 	]!
 	fs_uniforms_range := C.sg_range{
-		ptr: &tmp_fs_params
+		ptr: unsafe { &tmp_fs_params }
 		size: size_t(sizeof(tmp_fs_params))
 	}
 	gfx.apply_uniforms(C.SG_SHADERSTAGE_FS, C.SLOT_fs_params_p, &fs_uniforms_range)
@@ -469,7 +469,7 @@ fn draw_cube_glsl_p(app App) {
 		0 // padding bytes , see "fs_params" struct paddings in rt_glsl.h
 	]!
 	fs_uniforms_range := C.sg_range{
-		ptr: &tmp_fs_params
+		ptr: unsafe { &tmp_fs_params }
 		size: size_t(sizeof(tmp_fs_params))
 	}
 	gfx.apply_uniforms(C.SG_SHADERSTAGE_FS, C.SLOT_fs_params_p, &fs_uniforms_range)

examples/sokol/05_instancing_glsl/rt_glsl.v

@@ -331,7 +331,7 @@ fn draw_cube_glsl_i(mut app App){
 		app.inst_pos[index] = m4.Vec4{e:[f32((x - cx - app.camera_x) * cube_size),y ,f32( (z - cz - app.camera_z) * cube_size),spare_param]!}
 	}
 	range := C.sg_range{
-		ptr: &app.inst_pos
+		ptr: unsafe { &app.inst_pos }
 		size: size_t(num_inst * int(sizeof(m4.Vec4)))
 	}
 	gfx.update_buffer(app.bind['inst'].vertex_buffers[1], &range )
@@ -341,7 +341,7 @@ fn draw_cube_glsl_i(mut app App){
 	// passing the view matrix as uniform
 	// res is a 4x4 matrix of f32 thus: 4*16 byte of size
 	vs_uniforms_range := C.sg_range{
-		ptr: &tr_matrix
+		ptr: unsafe { &tr_matrix }
 		size: size_t(4 * 16)
 	}
 	gfx.apply_uniforms(C.SG_SHADERSTAGE_VS, C.SLOT_vs_params_i, &vs_uniforms_range)
@@ -359,7 +359,7 @@ fn draw_cube_glsl_i(mut app App){
 		0,0                        // padding bytes , see "fs_params" struct paddings in rt_glsl.h
 	]!
 	fs_uniforms_range := C.sg_range{
-		ptr: &tmp_fs_params
+		ptr: unsafe { &tmp_fs_params }
 		size: size_t(sizeof(tmp_fs_params))
 	}
 	gfx.apply_uniforms(C.SG_SHADERSTAGE_FS, C.SLOT_fs_params, &fs_uniforms_range)

examples/sokol/06_obj_viewer/obj/rend.v

@@ -235,7 +235,7 @@ pub fn (obj_part ObjPart) bind_and_draw(rend_data_index int, in_data Shader_data
 		size: size_t(in_data.vs_len)
 	}
 	fs_uniforms_range := C.sg_range{
-		ptr: &tmp_fs_params
+		ptr: unsafe { &tmp_fs_params }
 		size: size_t(in_data.fs_len)
 	}
 

examples/sokol/06_obj_viewer/show_obj.v

@@ -153,9 +153,9 @@ fn draw_model(app App, model_pos m4.Vec4) u32 {
 	tmp_fs_params.ligth = m4.vec3(x_light, radius_light, z_light)
 
 	sd := obj.Shader_data{
-		vs_data: &tmp_vs_param
+		vs_data: unsafe { &tmp_vs_param }
 		vs_len: int(sizeof(tmp_vs_param))
-		fs_data: &tmp_fs_params
+		fs_data: unsafe { &tmp_fs_params }
 		fs_len: int(sizeof(tmp_fs_params))
 	}
 

examples/term.ui/pong.v

@@ -210,7 +210,7 @@ fn (mut p Player) update() {
 		return
 	}
 	// dt := p.game.app.dt
-	ball := &p.game.ball
+	ball := unsafe { &p.game.ball }
 	// Evil AI that eventually will take over the world
 	p.pos.y = ball.pos.y - int(f32(p.racket_size) * 0.5)
 }
@@ -246,7 +246,7 @@ mut:
 }
 
 fn (mut g Game) move_player(id int, x int, y int) {
-	mut p := &g.players[id]
+	mut p := unsafe { &g.players[id] }
 	if p.ai { // disable AI when moved
 		p.ai = false
 	}
@@ -288,7 +288,7 @@ fn (mut g Game) new_round() {
 
 fn (mut g Game) update() {
 	dt := g.app.dt
-	mut b := &g.ball
+	mut b := unsafe { &g.ball }
 	for mut p in g.players {
 		p.update()
 		// Keep rackets within the game area

examples/ttf_font/example_ttf.v

@@ -53,7 +53,7 @@ fn draw_frame(mut app App_data) {
 		sgl.v2f(510, 400)
 		sgl.end()
 		// update the text
-		mut txt1 := &app.ttf_render[0]
+		mut txt1 := unsafe { &app.ttf_render[0] }
 		if app.frame_c % 2 == 0 {
 			txt1.destroy_texture()
 			txt1.create_text(cframe_txt, 43)
@@ -71,7 +71,7 @@ Frame: $app.frame_c
 But Vwill prevail for sure, V is the way!!
 òàèì@ò!£$%&
 "
-		txt1 = &app.ttf_render[1]
+		txt1 = unsafe { &app.ttf_render[1] }
 		if app.frame_c % 2 == 0 {
 			txt1.bmp.justify = false
 			if (app.frame_c >> 6) % 2 == 0 {
@@ -93,7 +93,7 @@ But Vwill prevail for sure, V is the way!!
 		txt1.draw_text_bmp(app.gg, 30 + (app.frame_c >> 1) & 0xFF, 200)
 		// draw mouse position
 		if app.mouse_x >= 0 {
-			txt1 = &app.ttf_render[2]
+			txt1 = unsafe { &app.ttf_render[2] }
 			txt1.destroy_texture()
 			txt1.create_text('$app.mouse_x,$app.mouse_y', 25)
 			txt1.create_texture()

vlib/cli/help.v

@@ -35,7 +35,7 @@ fn print_help_for_command(help_cmd Command) ? {
 			mut found := false
 			for sub_cmd in cmd.commands {
 				if sub_cmd.name == arg {
-					cmd = &sub_cmd
+					cmd = unsafe { &sub_cmd }
 					found = true
 					break
 				}

vlib/context/cancel.v

@@ -80,7 +80,7 @@ pub fn (mut ctx CancelContext) err() IError {
 
 pub fn (ctx CancelContext) value(key string) ?voidptr {
 	if key == cancel_context_key {
-		return voidptr(&ctx)
+		return voidptr(unsafe { &ctx })
 	}
 	return ctx.context.value(key)
 }

vlib/net/http/backend_nix.c.v

@@ -44,7 +44,7 @@ fn (req &Request) ssl_do(port int, method Method, host_name string, path string)
 	C.BIO_puts(web, &char(req_headers.str))
 	mut content := strings.new_builder(100)
 	mut buff := [bufsize]byte{}
-	bp := &buff[0]
+	bp := unsafe { &buff[0] }
 	mut readcounter := 0
 	for {
 		readcounter++

vlib/sync/channels.v

@@ -571,19 +571,19 @@ pub fn channel_select(mut channels []&Channel, dir []Direction, mut objrefs []vo
 	mut sem := unsafe { Semaphore{} }
 	sem.init(0)
 	for i, ch in channels {
-		subscr[i].sem = &sem
+		subscr[i].sem = unsafe { &sem }
 		if dir[i] == .push {
 			mut null16 := u16(0)
 			for !C.atomic_compare_exchange_weak_u16(&ch.write_sub_mtx, &null16, u16(1)) {
 				null16 = u16(0)
 			}
-			subscr[i].prev = &ch.write_subscriber
+			subscr[i].prev = unsafe { &ch.write_subscriber }
 			unsafe {
 				subscr[i].nxt = C.atomic_exchange_ptr(&voidptr(&ch.write_subscriber),
 					&subscr[i])
 			}
 			if voidptr(subscr[i].nxt) != voidptr(0) {
-				subscr[i].nxt.prev = &subscr[i].nxt
+				subscr[i].nxt.prev = unsafe { &subscr[i].nxt }
 			}
 			C.atomic_store_u16(&ch.write_sub_mtx, u16(0))
 		} else {
@@ -591,13 +591,13 @@ pub fn channel_select(mut channels []&Channel, dir []Direction, mut objrefs []vo
 			for !C.atomic_compare_exchange_weak_u16(&ch.read_sub_mtx, &null16, u16(1)) {
 				null16 = u16(0)
 			}
-			subscr[i].prev = &ch.read_subscriber
+			subscr[i].prev = unsafe { &ch.read_subscriber }
 			unsafe {
 				subscr[i].nxt = C.atomic_exchange_ptr(&voidptr(&ch.read_subscriber),
 					&subscr[i])
 			}
 			if voidptr(subscr[i].nxt) != voidptr(0) {
-				subscr[i].nxt.prev = &subscr[i].nxt
+				subscr[i].nxt.prev = unsafe { &subscr[i].nxt }
 			}
 			C.atomic_store_u16(&ch.read_sub_mtx, u16(0))
 		}

vlib/term/ui/input_nix.c.v

@@ -62,7 +62,7 @@ fn (mut ctx Context) shift(len int) {
 // TODO: don't actually do this, lmao
 [inline]
 fn (mut ctx Context) resize_arr(size int) {
-	mut l := &ctx.read_buf.len
+	mut l := unsafe { &ctx.read_buf.len }
 	unsafe {
 		*l = size
 		_ = l

vlib/v/ast/ast.v

@@ -495,6 +495,9 @@ pub mut:
 	// (for setting the position after the or block for autofree)
 	is_or        bool // `x := foo() or { ... }`
 	is_tmp       bool // for tmp for loop vars, so that autofree can skip them
+	is_auto_heap bool // value whoes address goes out of scope
+	is_heap_ref  bool // *known* to be pointer to heap memory (ptr to [heap] struct)
+	is_stack_obj bool // may be pointer to stack value (`mut` or `&` arg and not [heap] struct)
 }
 
 // used for smartcasting only

vlib/v/ast/table.v

@@ -7,6 +7,7 @@ import v.cflag
 import v.token
 import v.util
 
+[heap]
 pub struct Table {
 pub mut:
 	type_symbols     []TypeSymbol

vlib/v/checker/checker.v

@@ -61,6 +61,7 @@ pub mut:
 	inside_const   bool
 	inside_anon_fn bool
 	inside_ref_lit bool
+	inside_fn_arg  bool // `a`, `b` in `a.f(b)`
 	skip_flags     bool // should `#flag` and `#include` be skipped
 mut:
 	files                            []ast.File
@@ -1318,7 +1319,10 @@ pub fn (mut c Checker) call_expr(mut call_expr ast.CallExpr) ast.Type {
 	}
 	*/
 	// Now call `method_call` or `fn_call` for specific checks.
+	old_inside_fn_arg := c.inside_fn_arg
+	c.inside_fn_arg = true
 	typ := if call_expr.is_method { c.method_call(mut call_expr) } else { c.fn_call(mut call_expr) }
+	c.inside_fn_arg = old_inside_fn_arg
 	// autofree: mark args that have to be freed (after saving them in tmp exprs)
 	free_tmp_arg_vars := c.pref.autofree && !c.is_builtin_mod && call_expr.args.len > 0
 		&& !call_expr.args[0].typ.has_flag(.optional)
@@ -3564,7 +3568,7 @@ fn (mut c Checker) stmt(node ast.Stmt) {
 		ast.DeferStmt {
 			if node.idx_in_fn < 0 {
 				node.idx_in_fn = c.cur_fn.defer_stmts.len
-				c.cur_fn.defer_stmts << &node
+				c.cur_fn.defer_stmts << unsafe { &node }
 			}
 			c.stmts(node.stmts)
 		}
@@ -4176,7 +4180,7 @@ pub fn (mut c Checker) expr(node ast.Expr) ast.Type {
 		ast.AnonFn {
 			c.inside_anon_fn = true
 			keep_fn := c.cur_fn
-			c.cur_fn = &node.decl
+			c.cur_fn = unsafe { &node.decl }
 			c.stmts(node.decl.stmts)
 			c.fn_decl(mut node.decl)
 			c.cur_fn = keep_fn
@@ -5014,6 +5018,24 @@ pub fn (mut c Checker) match_expr(mut node ast.MatchExpr) ast.Type {
 	// node.expected_type = c.expected_type
 	// }
 	node.return_type = ret_type
+	cond_var := c.get_base_name(&node.cond)
+	if cond_var != '' {
+		mut cond_is_auto_heap := false
+		for branch in node.branches {
+			if v := branch.scope.find_var(cond_var) {
+				if v.is_auto_heap {
+					cond_is_auto_heap = true
+					break
+				}
+			}
+		}
+		if cond_is_auto_heap {
+			for branch in node.branches {
+				mut v := branch.scope.find_var(cond_var) or { continue }
+				v.is_auto_heap = true
+			}
+		}
+	}
 	return ret_type
 }
 
@@ -5830,6 +5852,53 @@ pub fn (mut c Checker) postfix_expr(mut node ast.PostfixExpr) ast.Type {
 	return typ
 }
 
+pub fn (mut c Checker) mark_as_referenced(mut node ast.Expr) {
+	match mut node {
+		ast.Ident {
+			if mut node.obj is ast.Var {
+				mut obj := unsafe { &node.obj }
+				if c.fn_scope != voidptr(0) {
+					obj = c.fn_scope.find_var(node.obj.name) or { unsafe { &node.obj } }
+				}
+				type_sym := c.table.get_type_symbol(obj.typ)
+				if obj.is_stack_obj {
+					c.error('`$node.name` cannot be referenced outside `unsafe` blocks as it might be stored on stack. Consider declaring `$type_sym.name` as `[heap]`.',
+						node.pos)
+				} else if type_sym.kind == .array_fixed {
+					c.error('cannot reference fixed array `$node.name` outside `unsafe` blocks as it is supposed to be stored on stack',
+						node.pos)
+				} else {
+					node.obj.is_auto_heap = true
+				}
+			}
+		}
+		ast.SelectorExpr {
+			c.mark_as_referenced(mut &node.expr)
+		}
+		ast.IndexExpr {
+			c.mark_as_referenced(mut &node.left)
+		}
+		else {}
+	}
+}
+
+pub fn (mut c Checker) get_base_name(node &ast.Expr) string {
+	match node {
+		ast.Ident {
+			return node.name
+		}
+		ast.SelectorExpr {
+			return c.get_base_name(&node.expr)
+		}
+		ast.IndexExpr {
+			return c.get_base_name(&node.left)
+		}
+		else {
+			return ''
+		}
+	}
+}
+
 pub fn (mut c Checker) prefix_expr(mut node ast.PrefixExpr) ast.Type {
 	old_inside_ref_lit := c.inside_ref_lit
 	c.inside_ref_lit = c.inside_ref_lit || node.op == .amp
@@ -5871,10 +5940,20 @@ pub fn (mut c Checker) prefix_expr(mut node ast.PrefixExpr) ast.Type {
 				}
 			}
 		}
+		if !c.inside_fn_arg && !c.inside_unsafe {
+			c.mark_as_referenced(mut &node.right)
+		}
 		return right_type.to_ptr()
 	} else if node.op == .amp && node.right !is ast.CastExpr {
+		if !c.inside_fn_arg && !c.inside_unsafe {
+			c.mark_as_referenced(mut &node.right)
+		}
+		if node.right.is_auto_deref_var() {
+			return right_type
+		} else {
 			return right_type.to_ptr()
 		}
+	}
 	if node.op == .mul {
 		if right_type.is_ptr() {
 			return right_type.deref()

vlib/v/checker/tests/function_missing_return_type.out

@@ -3,6 +3,13 @@ vlib/v/checker/tests/function_missing_return_type.vv:1:1: error: missing return
       | ~~~~~~~~~~
     2 | }
     3 |
+vlib/v/checker/tests/function_missing_return_type.vv:14:11: error: `s` cannot be referenced outside `unsafe` blocks as it might be stored on stack. Consider declaring `Abc` as `[heap]`.
+   12 | fn (s Abc) abc() &int {
+   13 |     if true {
+   14 |         return &s.x
+      |                 ^
+   15 |     }
+   16 |     s.panic(@FN)
 vlib/v/checker/tests/function_missing_return_type.vv:12:1: error: missing return at end of function `abc`
    10 | }
    11 | 

vlib/v/fmt/fmt.v

@@ -147,7 +147,7 @@ pub struct RemoveNewLineConfig {
 }
 
 pub fn (mut f Fmt) remove_new_line(cfg RemoveNewLineConfig) {
-	mut buffer := if cfg.imports_buffer { &f.out_imports } else { &f.out }
+	mut buffer := if cfg.imports_buffer { unsafe { &f.out_imports } } else { unsafe { &f.out } }
 	mut i := 0
 	for i = buffer.len - 1; i >= 0; i-- {
 		if !buffer.buf[i].is_space() { // != `\n` {

vlib/v/gen/c/cgen.v

@@ -2145,23 +2145,38 @@ fn (mut g Gen) gen_assign_stmt(assign_stmt ast.AssignStmt) {
 			g.expr(assign_stmt.right[0])
 			g.writeln(';')
 			for i, lx in assign_stmt.left {
+				mut is_auto_heap := false
 				if lx is ast.Ident {
 					if lx.kind == .blank_ident {
 						continue
 					}
+					if lx.obj is ast.Var {
+						is_auto_heap = lx.obj.is_auto_heap
+					}
 				}
 				styp := g.typ(assign_stmt.left_types[i])
 				if assign_stmt.op == .decl_assign {
 					g.write('$styp ')
+					if is_auto_heap {
+						g.write('*')
+					}
 				}
 				g.expr(lx)
 				if is_opt {
 					mr_base_styp := g.base_type(return_type)
+					if is_auto_heap {
+						g.writeln(' = HEAP($mr_base_styp, *($mr_base_styp*)${mr_var_name}.data).arg$i);')
+					} else {
 						g.writeln(' = (*($mr_base_styp*)${mr_var_name}.data).arg$i;')
+					}
+				} else {
+					if is_auto_heap {
+						g.writeln(' = HEAP($styp, ${mr_var_name}.arg$i);')
 					} else {
 						g.writeln(' = ${mr_var_name}.arg$i;')
 					}
 				}
+			}
 			return
 		}
 	}
@@ -2256,6 +2271,7 @@ fn (mut g Gen) gen_assign_stmt(assign_stmt ast.AssignStmt) {
 	}
 	// `a := 1` | `a,b := 1,2`
 	for i, left in assign_stmt.left {
+		mut is_auto_heap := false
 		mut var_type := assign_stmt.left_types[i]
 		mut val_type := assign_stmt.right_types[i]
 		val := assign_stmt.right[i]
@@ -2281,6 +2297,9 @@ fn (mut g Gen) gen_assign_stmt(assign_stmt ast.AssignStmt) {
 					var_type = var_type.set_flag(.atomic_f)
 				}
 			}
+			if left.obj is ast.Var {
+				is_auto_heap = left.obj.is_auto_heap
+			}
 		}
 		styp := g.typ(var_type)
 		mut is_fixed_array_init := false
@@ -2432,6 +2451,9 @@ fn (mut g Gen) gen_assign_stmt(assign_stmt ast.AssignStmt) {
 						g.out.write_string(util.tabs(g.indent - g.inside_ternary))
 					}
 					g.write('$styp ')
+					if is_auto_heap {
+						g.write('*')
+					}
 				}
 				if left is ast.Ident || left is ast.SelectorExpr {
 					g.prevent_sum_type_unwrapping_once = true
@@ -2511,10 +2533,16 @@ fn (mut g Gen) gen_assign_stmt(assign_stmt ast.AssignStmt) {
 							g.write('{0}')
 						}
 					} else {
+						if is_auto_heap {
+							g.write('HEAP($styp, (')
+						}
 						if val.is_auto_deref_var() {
 							g.write('*')
 						}
 						g.expr(val)
+						if is_auto_heap {
+							g.write('))')
+						}
 					}
 				} else {
 					if assign_stmt.has_cross_var {
@@ -2842,9 +2870,9 @@ fn (mut g Gen) map_fn_ptrs(key_typ ast.TypeSymbol) (string, string, string, stri
 		}
 		.voidptr {
 			ts := if g.pref.m64 {
-				&g.table.type_symbols[ast.u64_type_idx]
+				unsafe { &g.table.type_symbols[ast.u64_type_idx] }
 			} else {
-				&g.table.type_symbols[ast.u32_type_idx]
+				unsafe { &g.table.type_symbols[ast.u32_type_idx] }
 			}
 			return g.map_fn_ptrs(ts)
 		}
@@ -3123,7 +3151,9 @@ fn (mut g Gen) expr(node ast.Expr) {
 				}
 			} else {
 				// g.write('/*pref*/')
+				if !(g.is_amp && node.right.is_auto_deref_var()) {
 					g.write(node.op.str())
+				}
 				// g.write('(')
 				g.expr(node.right)
 			}
@@ -4355,6 +4385,7 @@ fn (mut g Gen) ident(node ast.Ident) {
 	mut name := c_name(node.name)
 	// TODO: temporary, remove this
 	node_info := node.info
+	mut is_auto_heap := false
 	if node_info is ast.IdentVar {
 		// x ?int
 		// `x = 10` => `x.data = 10` (g.right_is_opt == false)
@@ -4372,12 +4403,16 @@ fn (mut g Gen) ident(node ast.Ident) {
 		}
 		scope := g.file.scope.innermost(node.pos.pos)
 		if v := scope.find_var(node.name) {
+			is_auto_heap = v.is_auto_heap && (!g.is_assign_lhs || g.assign_op != .decl_assign)
+			if is_auto_heap {
+				g.write('(*(')
+			}
 			if v.smartcasts.len > 0 {
 				v_sym := g.table.get_type_symbol(v.typ)
 				if !prevent_sum_type_unwrapping_once {
 					for _ in v.smartcasts {
 						g.write('(')
-						if v_sym.kind == .sum_type {
+						if v_sym.kind == .sum_type && !is_auto_heap {
 							g.write('*')
 						}
 					}
@@ -4390,7 +4425,7 @@ fn (mut g Gen) ident(node ast.Ident) {
 								is_ptr = true
 							}
 						}
-						dot := if is_ptr { '->' } else { '.' }
+						dot := if is_ptr || is_auto_heap { '->' } else { '.' }
 						if mut cast_sym.info is ast.Aggregate {
 							sym := g.table.get_type_symbol(cast_sym.info.types[g.aggregate_type_idx])
 							g.write('${dot}_$sym.cname')
@@ -4399,6 +4434,9 @@ fn (mut g Gen) ident(node ast.Ident) {
 						}
 						g.write(')')
 					}
+					if is_auto_heap {
+						g.write('))')
+					}
 					return
 				}
 			}
@@ -4413,6 +4451,9 @@ fn (mut g Gen) ident(node ast.Ident) {
 		}
 	}
 	g.write(g.get_ternary_name(name))
+	if is_auto_heap {
+		g.write('))')
+	}
 }
 
 fn (mut g Gen) cast_expr(node ast.CastExpr) {
@@ -4622,11 +4663,22 @@ fn (mut g Gen) if_expr(node ast.IfExpr) {
 							g.write('\t$base_type $cond_var_name = ')
 							g.expr(branch.cond.expr)
 							g.writeln(';')
+						} else {
+							mut is_auto_heap := false
+							if branch.stmts.len > 0 {
+								scope := g.file.scope.innermost(ast.Node(branch.stmts[branch.stmts.len - 1]).position().pos)
+								if v := scope.find_var(branch.cond.var_name) {
+									is_auto_heap = v.is_auto_heap
+								}
+							}
+							if is_auto_heap {
+								g.writeln('\t$base_type* $branch.cond.var_name = HEAP($base_type, *($base_type*)${var_name}.data);')
 							} else {
 								g.writeln('\t$base_type $branch.cond.var_name = *($base_type*)${var_name}.data;')
 							}
 						}
 					}
+				}
 				else {
 					g.write('if (')
 					g.expr(branch.cond)

vlib/v/gen/c/fn.v

@@ -69,7 +69,9 @@ fn (mut g Gen) process_fn_decl(node ast.FnDecl) {
 		}
 	}
 	keep_fn_decl := g.fn_decl
+	unsafe {
 		g.fn_decl = &node
+	}
 	if node.name == 'main.main' {
 		g.has_main = true
 	}

vlib/v/gen/js/js.v

@@ -387,7 +387,7 @@ fn (mut g JsGen) stmt(node ast.Stmt) {
 			g.gen_expr_stmt(node)
 		}
 		ast.FnDecl {
-			g.fn_decl = &node
+			g.fn_decl = unsafe { &node }
 			g.gen_fn_decl(node)
 		}
 		ast.ForCStmt {
@@ -813,7 +813,9 @@ fn fn_has_go(node ast.FnDecl) bool {
 }
 
 fn (mut g JsGen) gen_method_decl(it ast.FnDecl) {
+	unsafe {
 		g.fn_decl = &it
+	}
 	has_go := fn_has_go(it)
 	is_main := it.name == 'main.main'
 	g.gen_attrs(it.attrs)

vlib/v/parser/assign.v

@@ -152,6 +152,7 @@ fn (mut p Parser) partial_assign_stmt(left []ast.Expr, left_comments []ast.Comme
 						share: share
 						is_mut: lx.is_mut || p.inside_for
 						pos: lx.pos
+						is_stack_obj: p.inside_for
 					}
 					if p.pref.autofree {
 						if r0 is ast.CallExpr {

vlib/v/parser/fn.v

@@ -291,11 +291,28 @@ fn (mut p Parser) fn_decl() ast.FnDecl {
 					scope: 0
 				}
 			}
+			mut is_heap_ref := false // args are only borrowed, so assume maybe on stack
+			mut is_stack_obj := true
+			nr_muls := param.typ.nr_muls()
+			if nr_muls == 1 { // mut a St, b &St
+				base_type_sym := p.table.get_type_symbol(param.typ.set_nr_muls(0))
+				if base_type_sym.kind == .struct_ {
+					info := base_type_sym.info as ast.Struct
+					is_heap_ref = info.is_heap // if type is declared as [heap] we can assume this, too
+					is_stack_obj = !is_heap_ref
+				}
+			}
+			if param.typ.has_flag(.shared_f) {
+				is_heap_ref = true
+				is_stack_obj = false
+			}
 			p.scope.register(ast.Var{
 				name: param.name
 				typ: param.typ
 				is_mut: param.is_mut
 				is_auto_deref: param.is_mut || param.is_auto_rec
+				is_heap_ref: is_heap_ref
+				is_stack_obj: is_stack_obj
 				pos: param.pos
 				is_used: true
 				is_arg: true
@@ -580,6 +597,21 @@ fn (mut p Parser) anon_fn() ast.AnonFn {
 		if arg.name.len == 0 {
 			p.error_with_pos('use `_` to name an unused parameter', arg.pos)
 		}
+		mut is_heap_ref := false // args are only borrowed, so assume maybe on stack
+		mut is_stack_obj := true
+		nr_muls := arg.typ.nr_muls()
+		if nr_muls == 1 { // mut a St, b &St
+			base_type_sym := p.table.get_type_symbol(arg.typ.set_nr_muls(0))
+			if base_type_sym.kind == .struct_ {
+				info := base_type_sym.info as ast.Struct
+				is_heap_ref = info.is_heap // if type is declared as [heap] we can assume this, too
+				is_stack_obj = !is_heap_ref
+			}
+		}
+		if arg.typ.has_flag(.shared_f) {
+			is_heap_ref = true
+			is_stack_obj = false
+		}
 		p.scope.register(ast.Var{
 			name: arg.name
 			typ: arg.typ
@@ -587,6 +619,8 @@ fn (mut p Parser) anon_fn() ast.AnonFn {
 			pos: arg.pos
 			is_used: true
 			is_arg: true
+			is_heap_ref: is_heap_ref
+			is_stack_obj: is_stack_obj
 		})
 	}
 	mut same_line := p.tok.line_nr == p.prev_tok.line_nr

vlib/v/parser/for.v

@@ -122,6 +122,7 @@ fn (mut p Parser) for_stmt() ast.Stmt {
 				typ: ast.int_type
 				pos: key_var_pos
 				is_tmp: true
+				is_stack_obj: true
 			})
 		} else if p.scope.known_var(val_var_name) {
 			return p.error('redefinition of value iteration variable `$val_var_name`')
@@ -146,6 +147,7 @@ fn (mut p Parser) for_stmt() ast.Stmt {
 				typ: ast.int_type
 				pos: val_var_pos
 				is_tmp: true
+				is_stack_obj: true
 			})
 			if key_var_name.len > 0 {
 				return p.error_with_pos('cannot declare index variable with range `for`',
@@ -159,6 +161,7 @@ fn (mut p Parser) for_stmt() ast.Stmt {
 				is_mut: val_is_mut
 				is_auto_deref: val_is_mut
 				is_tmp: true
+				is_stack_obj: true
 			})
 		}
 		p.inside_for = false

vlib/v/parser/if_match.v

@@ -54,6 +54,7 @@ fn (mut p Parser) if_expr(is_comptime bool) ast.IfExpr {
 						typ: ast.error_type
 						pos: p.tok.position()
 						is_used: true
+						is_stack_obj: true
 					})
 				}
 				branches << ast.IfBranch{

vlib/v/parser/parser.v

@@ -2258,6 +2258,7 @@ fn (mut p Parser) dot_expr(left ast.Expr) ast.Expr {
 				typ: ast.error_type
 				pos: p.tok.position()
 				is_used: true
+				is_stack_obj: true
 			})
 			or_kind = .block
 			or_stmts = p.parse_block_no_scope(false)

vlib/v/parser/pratt.v

@@ -471,6 +471,7 @@ fn (mut p Parser) infix_expr(left ast.Expr) ast.Expr {
 				typ: ast.error_type
 				pos: p.tok.position()
 				is_used: true
+				is_stack_obj: true
 			})
 			or_kind = .block
 			or_stmts = p.parse_block_no_scope(false)
@@ -553,6 +554,7 @@ fn (mut p Parser) prefix_expr() ast.PrefixExpr {
 				typ: ast.error_type
 				pos: p.tok.position()
 				is_used: true
+				is_stack_obj: true
 			})
 			or_kind = .block
 			or_stmts = p.parse_block_no_scope(false)

vlib/v/tests/mut_receiver_returned_as_reference_test.v

@@ -18,7 +18,7 @@ fn (mut p Player) set_position(x int, y int) &Player {
 	// TODO: from the point of view of the V programmer,
 	// `p` has still type &Player.
 	// assert typeof(p).name == 'Player'
-	return &p
+	return unsafe { &p }
 }
 
 fn test_mut_receiver() {

vlib/v/tests/mut_test.v

@@ -268,7 +268,7 @@ mut:
 }
 
 fn foo4(mut f Foo) {
-	f2 := &f
+	f2 := unsafe { &f }
 	f.foo = 100
 	println(f.foo)
 	println(f2.foo)
@@ -284,7 +284,7 @@ fn test_mut_13() {
 }
 
 fn foo5(mut arr []int) {
-	arr2 := &arr
+	arr2 := unsafe { &arr }
 	arr[0] = 0
 	println(arr[0]) // 0
 	assert arr[0] == 0
@@ -300,7 +300,7 @@ fn test_mut_14() {
 }
 
 fn foo6(mut arr [3]int) {
-	arr2 := &arr
+	arr2 := unsafe { &arr }
 	arr[0] = 0
 	println(arr[0]) // 0
 	assert arr[0] == 0
@@ -316,7 +316,7 @@ fn test_mut_15() {
 }
 
 fn foo7(mut m map[string]int) {
-	m2 := &m
+	m2 := unsafe { &m }
 	m['one'] = 1
 	println(m['one']) // 1
 	assert m['one'] == 1

vlib/v/tests/ptr_arithmetic_test.v

@@ -48,8 +48,8 @@ fn test_ptr_arithmetic_over_struct() {
 	a[0].x = 10
 	a[1].x = 100
 	a[2].x = 1000
-	mut pa := &a[0]
+	mut pa := unsafe { &a[0] }
-	assert pa == &a[0]
+	assert pa == unsafe { &a[0] }
 	unsafe {
 		assert pa.x == 10
 		pa++
@@ -66,5 +66,5 @@ fn test_ptr_arithmetic_over_struct() {
 		assert pa.x == 1000
 		pa -= 2
 	}
-	assert pa == &a[0]
+	assert pa == unsafe { &a[0] }
 }

vlib/v/tests/reference_return_test.v

@@ -0,0 +1,25 @@
+struct Qwe {
+mut:
+	a f64
+}
+
+fn f() &Qwe {
+	q := Qwe{
+		a: 12.5
+	}
+	return &q
+}
+
+fn g() f64 {
+	a := -0.125
+	b := 3
+	c := a * b
+	return c
+}
+
+fn test_reference_return() {
+	x := f()
+	y := g()
+	assert x.a == 12.5
+	assert y == -0.375
+}

vlib/v/tests/type_voidptr_test.v

@@ -15,7 +15,7 @@ fn memcpy(mut dest voidptr, src voidptr, len u32) voidptr {
 fn test_mut_voidptr_arg() {
 	mut a := [1, 2]!
 	b := [3, 4]!
-	mut aptr := voidptr(&a[0])
+	mut aptr := voidptr(unsafe { &a[0] })
 	unsafe { memcpy(mut aptr, &b[0], sizeof(int)) }
 	assert a == [3, 2]!
 }