func (b *builder) forStmt(fn *Function, s *ast.ForStmt, label *lblock) {
	//	...init...
	//      jump loop
	// loop:
	//      if cond goto body else done
	// body:
	//      ...body...
	//      jump post
	// post:				 (target of continue)
	//      ...post...
	//      jump loop
	// done:                                 (target of break)
	if s.Init != nil {
		b.stmt(fn, s.Init)
	}
	body := fn.newBasicBlock("for.body")
	done := fn.newBasicBlock("for.done") // target of 'break'
	loop := body                         // target of back-edge
	if s.Cond != nil {
		loop = fn.newBasicBlock("for.loop")
	}
	cont := loop // target of 'continue'
	if s.Post != nil {
		cont = fn.newBasicBlock("for.post")
	}
	if label != nil {
		label._break = done
		label._continue = cont
	}
	emitJump(fn, loop)
	fn.currentBlock = loop
	if loop != body {
		b.cond(fn, s.Cond, body, done)
		fn.currentBlock = body
	}
	fn.targets = &targets{
		tail:      fn.targets,
		_break:    done,
		_continue: cont,
	}
	b.stmt(fn, s.Body)
	fn.targets = fn.targets.tail
	emitJump(fn, cont)

	if s.Post != nil {
		fn.currentBlock = cont
		b.stmt(fn, s.Post)
		emitJump(fn, loop) // back-edge
	}
	fn.currentBlock = done
}
func (b *builder) forStmt(fn *Function, s *ast.ForStmt, label *lblock) {
	//	...init...
	//      jump loop
	// loop:
	//      if cond goto body else done
	// body:
	//      ...body...
	//      jump post
	// post:				 (target of continue)
	//      ...post...
	//      jump loop
	// done:                                 (target of break)
	if s.Init != nil {
		b.stmt(fn, s.Init)
	}
	body := fn.newBasicBlock("for.body")
	done := fn.newBasicBlock("for.done") // target of 'break'
	loop := body                         // target of back-edge
	if s.Cond != nil {
		loop = fn.newBasicBlock("for.loop")
	}
	cont := loop // target of 'continue'
	if s.Post != nil {
		cont = fn.newBasicBlock("for.post")
	}
	if label != nil {
		label._break = done
		label._continue = cont
	}
	emitJump(fn, loop)
	fn.currentBlock = loop
	if loop != body {
		b.cond(fn, s.Cond, body, done)
		fn.currentBlock = body
	}
	fn.targets = &targets{
		tail:      fn.targets,
		_break:    done,
		_continue: cont,
	}
	b.stmt(fn, s.Body)
	fn.targets = fn.targets.tail
	emitJump(fn, cont)

	if s.Post != nil {
		fn.currentBlock = cont
		b.stmt(fn, s.Post)
		emitJump(fn, loop) // back-edge
	}
	fn.currentBlock = done
}
// forStmt emits to fn code for the for statement s, optionally
// labelled by label.
//