native: initial support for `defer` (#14779)

vlib/v/gen/native/amd64.v

@@ -1903,7 +1903,7 @@ fn (mut g Gen) for_stmt(node ast.ForStmt) {
 fn (mut g Gen) fn_decl_amd64(node ast.FnDecl) {
 	g.push(.rbp)
 	g.mov_rbp_rsp()
-	locals_count := node.scope.objects.len + node.params.len
+	locals_count := node.scope.objects.len + node.params.len + node.defer_stmts.len
 	g.stackframe_size = (locals_count * 8) + 0x10
 	g.sub8(.rsp, g.stackframe_size)
 
@@ -1917,6 +1917,11 @@ fn (mut g Gen) fn_decl_amd64(node ast.FnDecl) {
 		offset += 4
 		g.mov_reg_to_var(offset, native.fn_arg_registers[i])
 	}
+	// define defer vars
+	for i in 0 .. node.defer_stmts.len {
+		name := '_defer$i'
+		g.allocate_var(name, 8, 0)
+	}
 	//
 	g.stmts(node.stmts)
 	is_main := node.name == 'main.main'
@@ -1930,6 +1935,24 @@ fn (mut g Gen) fn_decl_amd64(node ast.FnDecl) {
 	// g.leave()
 	g.labels.addrs[0] = g.pos()
 	g.println('; label 0: return')
+	if g.defer_stmts.len != 0 {
+		// save return value
+		g.push(.rax)
+		for defer_stmt in g.defer_stmts.reverse() {
+			defer_var := g.get_var_offset('_defer$defer_stmt.idx_in_fn')
+			g.mov_var_to_reg(.rax, defer_var)
+			g.cmp_zero(.rax)
+			label := g.labels.new_label()
+			jump_addr := g.cjmp(.je)
+			g.labels.patches << LabelPatch{
+				id: label
+				pos: jump_addr
+			}
+			g.stmts(defer_stmt.stmts)
+			g.labels.addrs[label] = g.pos()
+		}
+		g.pop(.rax)
+	}
 	g.add8(.rsp, g.stackframe_size)
 	g.pop(.rbp)
 	g.ret()

vlib/v/gen/native/gen.v

@@ -48,6 +48,7 @@ mut:
 	callpatches          []CallPatch
 	strs                 []String
 	labels               &LabelTable
+	defer_stmts          []ast.DeferStmt
 }
 
 enum RelocType {
@@ -72,7 +73,6 @@ struct CallPatch {
 struct LabelTable {
 mut:
 	label_id int
-	return_ids []int = [0] // array is for defer
 	addrs    []i64 = [i64(0)] // register address of label here
 	patches  []LabelPatch // push placeholders
 	branches []BranchLabel
@@ -489,6 +489,7 @@ fn (mut g Gen) fn_decl(node ast.FnDecl) {
 	g.stack_var_pos = 0
 	g.register_function_address(node.name)
 	g.labels = &LabelTable{}
+	g.defer_stmts.clear()
 	if g.pref.arch == .arm64 {
 		g.fn_decl_arm64(node)
 	} else {
@@ -678,6 +679,12 @@ fn (mut g Gen) stmt(node ast.Stmt) {
 			}
 		}
 		ast.ConstDecl {}
+		ast.DeferStmt {
+			defer_var := g.get_var_offset('_defer$g.defer_stmts.len')
+			g.mov_int_to_var(defer_var, ._8, 1)
+			g.defer_stmts << node
+			g.defer_stmts[g.defer_stmts.len - 1].idx_in_fn = g.defer_stmts.len - 1
+		}
 		ast.ExprStmt {
 			g.expr(node.expr)
 		}
@@ -714,6 +721,7 @@ fn (mut g Gen) stmt(node ast.Stmt) {
 			// dump(node)
 			// dump(node.types)
 			mut s := '?' //${node.exprs[0].val.str()}'
+			// TODO: void return
 			e0 := node.exprs[0]
 			match e0 {
 				ast.IntegerLiteral {
@@ -740,7 +748,7 @@ fn (mut g Gen) stmt(node ast.Stmt) {
 			}
 
 			// jump to return label
-			label := g.labels.return_ids.last()
+			label := 0
 			pos := g.jmp(0)
 			g.labels.patches << LabelPatch{
 				id: label

vlib/v/gen/native/tests/defer.vv

@@ -0,0 +1,38 @@
+fn defer_test() {
+	println('normal1')
+	defer {
+		println('defer1')
+	}
+	defer {
+		println('defer2')
+	}
+	println('normal2')
+}
+
+fn defer_condition_test(i int) {
+	if i > 3 {
+		defer {
+			println('defer1')
+		}
+	} else {
+		defer {
+			println('defer2')
+		}
+	}
+}
+
+fn defer_return_test() int {
+	mut i := 1
+	defer {
+		i = 3
+	}
+	return i
+}
+
+fn main() {
+	defer_test()
+	defer_condition_test(1)
+	defer_condition_test(6)
+	a := defer_return_test()
+	println(a)
+}

vlib/v/gen/native/tests/defer.vv.out

@@ -0,0 +1,7 @@
+normal1
+normal2
+defer2
+defer1
+defer2
+defer1
+1