func (b *builder) stmt(fn *Function, _s ast.Stmt) {
	// The label of the current statement.  If non-nil, its _goto
	// target is always set; its _break and _continue are set only
	// within the body of switch/typeswitch/select/for/range.
	// It is effectively an additional default-nil parameter of stmt().
	var label *lblock
start:
	switch s := _s.(type) {
	case *ast.EmptyStmt:
		// ignore.  (Usually removed by gofmt.)

	case *ast.DeclStmt: // Con, Var or Typ
		d := s.Decl.(*ast.GenDecl)
		if d.Tok == token.VAR {
			for _, spec := range d.Specs {
				if vs, ok := spec.(*ast.ValueSpec); ok {
					b.localValueSpec(fn, vs)
				}
			}
		}

	case *ast.LabeledStmt:
		label = fn.labelledBlock(s.Label)
		emitJump(fn, label._goto)
		fn.currentBlock = label._goto
		_s = s.Stmt
		goto start // effectively: tailcall stmt(fn, s.Stmt, label)

	case *ast.ExprStmt:
		b.expr(fn, s.X)

	case *ast.SendStmt:
		fn.emit(&Send{
			Chan: b.expr(fn, s.Chan),
			X: emitConv(fn, b.expr(fn, s.Value),
				fn.Pkg.typeOf(s.Chan).Underlying().(*types.Chan).Elem()),
			pos: s.Arrow,
		})

	case *ast.IncDecStmt:
		op := token.ADD
		if s.Tok == token.DEC {
			op = token.SUB
		}
		loc := b.addr(fn, s.X, false)
		b.assignOp(fn, loc, NewConst(exact.MakeInt64(1), loc.typ()), op, s.Pos())

	case *ast.AssignStmt:
		switch s.Tok {
		case token.ASSIGN, token.DEFINE:
			b.assignStmt(fn, s.Lhs, s.Rhs, s.Tok == token.DEFINE)

		default: // +=, etc.
			op := s.Tok + token.ADD - token.ADD_ASSIGN
			b.assignOp(fn, b.addr(fn, s.Lhs[0], false), b.expr(fn, s.Rhs[0]), op, s.Pos())
		}

	case *ast.GoStmt:
		// The "intrinsics" new/make/len/cap are forbidden here.
		// panic is treated like an ordinary function call.
		v := Go{pos: s.Go}
		b.setCall(fn, s.Call, &v.Call)
		fn.emit(&v)

	case *ast.DeferStmt:
		// The "intrinsics" new/make/len/cap are forbidden here.
		// panic is treated like an ordinary function call.
		v := Defer{pos: s.Defer}
		b.setCall(fn, s.Call, &v.Call)
		fn.emit(&v)

		// A deferred call can cause recovery from panic,
		// and control resumes at the Recover block.
		createRecoverBlock(fn)

	case *ast.ReturnStmt:
		var results []Value
		if len(s.Results) == 1 && fn.Signature.Results().Len() > 1 {
			// Return of one expression in a multi-valued function.
			tuple := b.exprN(fn, s.Results[0])
			ttuple := tuple.Type().(*types.Tuple)
			for i, n := 0, ttuple.Len(); i < n; i++ {
				results = append(results,
					emitConv(fn, emitExtract(fn, tuple, i),
						fn.Signature.Results().At(i).Type()))
			}
		} else {
			// 1:1 return, or no-arg return in non-void function.
			for i, r := range s.Results {
				v := emitConv(fn, b.expr(fn, r), fn.Signature.Results().At(i).Type())
				results = append(results, v)
			}
		}
		if fn.namedResults != nil {
			// Function has named result parameters (NRPs).
			// Perform parallel assignment of return operands to NRPs.
			for i, r := range results {
				emitStore(fn, fn.namedResults[i], r, s.Return)
			}
		}
		// Run function calls deferred in this
		// function when explicitly returning from it.
		fn.emit(new(RunDefers))
		if fn.namedResults != nil {
			// Reload NRPs to form the result tuple.
			results = results[:0]
			for _, r := range fn.namedResults {
				results = append(results, emitLoad(fn, r))
			}
		}
		fn.emit(&Return{Results: results, pos: s.Return})
		fn.currentBlock = fn.newBasicBlock("unreachable")

	case *ast.BranchStmt:
		var block *BasicBlock
		switch s.Tok {
		case token.BREAK:
			if s.Label != nil {
				block = fn.labelledBlock(s.Label)._break
			} else {
				for t := fn.targets; t != nil && block == nil; t = t.tail {
					block = t._break
				}
			}

		case token.CONTINUE:
			if s.Label != nil {
				block = fn.labelledBlock(s.Label)._continue
			} else {
				for t := fn.targets; t != nil && block == nil; t = t.tail {
					block = t._continue
				}
			}

		case token.FALLTHROUGH:
			for t := fn.targets; t != nil && block == nil; t = t.tail {
				block = t._fallthrough
			}

		case token.GOTO:
			block = fn.labelledBlock(s.Label)._goto
		}
		emitJump(fn, block)
		fn.currentBlock = fn.newBasicBlock("unreachable")

	case *ast.BlockStmt:
		b.stmtList(fn, s.List)

	case *ast.IfStmt:
		if s.Init != nil {
			b.stmt(fn, s.Init)
		}
		then := fn.newBasicBlock("if.then")
		done := fn.newBasicBlock("if.done")
		els := done
		if s.Else != nil {
			els = fn.newBasicBlock("if.else")
		}
		b.cond(fn, s.Cond, then, els)
		fn.currentBlock = then
		b.stmt(fn, s.Body)
		emitJump(fn, done)

		if s.Else != nil {
			fn.currentBlock = els
			b.stmt(fn, s.Else)
			emitJump(fn, done)
		}

		fn.currentBlock = done

	case *ast.SwitchStmt:
		b.switchStmt(fn, s, label)

	case *ast.TypeSwitchStmt:
		b.typeSwitchStmt(fn, s, label)

	case *ast.SelectStmt:
		b.selectStmt(fn, s, label)

	case *ast.ForStmt:
		b.forStmt(fn, s, label)

	case *ast.RangeStmt:
		b.rangeStmt(fn, s, label)

	default:
		panic(fmt.Sprintf("unexpected statement kind: %T", s))
	}
}
func (b *builder) stmt(fn *Function, _s ast.Stmt) {
	// The label of the current statement.  If non-nil, its _goto
	// target is always set; its _break and _continue are set only
	// within the body of switch/typeswitch/select/for/range.
	// It is effectively an additional default-nil parameter of stmt().
	var label *lblock
start:
	switch s := _s.(type) {
	case *ast.EmptyStmt:
		// ignore.  (Usually removed by gofmt.)

	case *ast.DeclStmt: // Con, Var or Typ
		d := s.Decl.(*ast.GenDecl)
		if d.Tok == token.VAR {
			for _, spec := range d.Specs {
				if vs, ok := spec.(*ast.ValueSpec); ok {
					b.localValueSpec(fn, vs)
				}
			}
		}

	case *ast.LabeledStmt:
		label = fn.labelledBlock(s.Label)
		emitJump(fn, label._goto)
		fn.currentBlock = label._goto
		_s = s.Stmt
		goto start // effectively: tailcall stmt(fn, s.Stmt, label)

	case *ast.ExprStmt:
		b.expr(fn, s.X)

	case *ast.SendStmt:
		fn.emit(&Send{
			Chan: b.expr(fn, s.Chan),
			X: emitConv(fn, b.expr(fn, s.Value),
				fn.Pkg.typeOf(s.Chan).Underlying().(*types.Chan).Elem()),
			pos: s.Arrow,
		})

	case *ast.IncDecStmt:
		op := token.ADD
		if s.Tok == token.DEC {
			op = token.SUB
		}
		loc := b.addr(fn, s.X, false)
		b.assignOp(fn, loc, NewConst(exact.MakeInt64(1), loc.typ()), op, s.Pos())

	case *ast.AssignStmt:
		switch s.Tok {
		case token.ASSIGN, token.DEFINE:
			b.assignStmt(fn, s.Lhs, s.Rhs, s.Tok == token.DEFINE)

		default: // +=, etc.
			op := s.Tok + token.ADD - token.ADD_ASSIGN
			b.assignOp(fn, b.addr(fn, s.Lhs[0], false), b.expr(fn, s.Rhs[0]), op, s.Pos())
		}

	case *ast.GoStmt:
		// The "intrinsics" new/make/len/cap are forbidden here.
		// panic is treated like an ordinary function call.
		v := Go{pos: s.Go}
		b.setCall(fn, s.Call, &v.Call)
		fn.emit(&v)

	case *ast.DeferStmt:
		// The "intrinsics" new/make/len/cap are forbidden here.
		// panic is treated like an ordinary function call.
		v := Defer{pos: s.Defer}
		b.setCall(fn, s.Call, &v.Call)
		fn.emit(&v)

		// A deferred call can cause recovery from panic,
		// and control resumes at the Recover block.
		createRecoverBlock(fn)

	case *ast.ReturnStmt:
		var results []Value
		if len(s.Results) == 1 && fn.Signature.Results().Len() > 1 {
			// Return of one expression in a multi-valued function.
			tuple := b.exprN(fn, s.Results[0])
			ttuple := tuple.Type().(*types.Tuple)
			for i, n := 0, ttuple.Len(); i < n; i++ {
				results = append(results,
					emitConv(fn, emitExtract(fn, tuple, i),
						fn.Signature.Results().At(i).Type()))
			}
		} else {
			// 1:1 return, or no-arg return in non-void function.
			for i, r := range s.Results {
				v := emitConv(fn, b.expr(fn, r), fn.Signature.Results().At(i).Type())
				results = append(results, v)
			}
		}
		if fn.namedResults != nil {
			// Function has named result parameters (NRPs).
			// Perform parallel assignment of return operands to NRPs.
			for i, r := range results {
				emitStore(fn, fn.namedResults[i], r, s.Return)
			}
		}
		// Run function calls deferred in this
		// function when explicitly returning from it.
		fn.emit(new(RunDefers))
		if fn.namedResults != nil {
			// Reload NRPs to form the result tuple.
			results = results[:0]
			for _, r := range fn.namedResults {
				results = append(results, emitLoad(fn, r))
			}
		}
		fn.emit(&Return{Results: results, pos: s.Return})
		fn.currentBlock = fn.newBasicBlock("unreachable")

	case *ast.BranchStmt:
		var block *BasicBlock
		switch s.Tok {
		case token.BREAK:
			if s.Label != nil {
				block = fn.labelledBlock(s.Label)._break
			} else {
				for t := fn.targets; t != nil && block == nil; t = t.tail {
					block = t._break
				}
			}

		case token.CONTINUE:
			if s.Label != nil {
				block = fn.labelledBlock(s.Label)._continue
			} else {
				for t := fn.targets; t != nil && block == nil; t = t.tail {
					block = t._continue
				}
			}

		case token.FALLTHROUGH:
			for t := fn.targets; t != nil && block == nil; t = t.tail {
				block = t._fallthrough
			}

		case token.GOTO:
			block = fn.labelledBlock(s.Label)._goto
		}
		emitJump(fn, block)
		fn.currentBlock = fn.newBasicBlock("unreachable")

	case *ast.BlockStmt:
		b.stmtList(fn, s.List)

	case *ast.IfStmt:
		if s.Init != nil {
			b.stmt(fn, s.Init)
		}
		then := fn.newBasicBlock("if.then")
		done := fn.newBasicBlock("if.done")
		els := done
		if s.Else != nil {
			els = fn.newBasicBlock("if.else")
		}
		b.cond(fn, s.Cond, then, els)
		fn.currentBlock = then
		b.stmt(fn, s.Body)
		emitJump(fn, done)

		if s.Else != nil {
			fn.currentBlock = els
			b.stmt(fn, s.Else)
			emitJump(fn, done)
		}

		fn.currentBlock = done

	case *ast.SwitchStmt:
		b.switchStmt(fn, s, label)

	case *ast.TypeSwitchStmt:
		b.typeSwitchStmt(fn, s, label)

	case *ast.SelectStmt:
		b.selectStmt(fn, s, label)

	case *ast.ForStmt:
		b.forStmt(fn, s, label)

	case *ast.RangeStmt:
		b.rangeStmt(fn, s, label)

	default:
		panic(fmt.Sprintf("unexpected statement kind: %T", s))
	}
}
// stmt lowers statement s to SSA form, emitting code to fn.