The "range" clause in a "for-range" loop now accepts iterator functions of the following types

	func(func() bool)
	func(func(K) bool)
	func(func(K, V) bool)

as range expressions.
Calls of the iterator argument function produce the iteration values for the "for-range" loop.
For details see the [language spec](/ref/spec#For_statements).

	// make sure we don't get into an infinite loop with phi values.
	c := testConfig(t)
	ptrType := c.config.Types.BytePtr
	fun := c.Fun("entry",
		Bloc("entry",
			Valu("start", OpInitMem, types.TypeMem, 0, nil),
			Valu("sb", OpSB, c.config.Types.Uintptr, 0, nil),
			Valu("v", OpConstBool, c.config.Types.Bool, 1, nil),
			Valu("addr", OpAddr, ptrType, 0, nil, "sb"),
			Goto("loop")),
		Bloc("loop",

#include "go_asm.h"
#include "textflag.h"

// memequal(p, q unsafe.Pointer, size uintptr) bool
TEXT runtime·memequal(SB), NOSPLIT, $0-25
	Get SP
	I64Load a+0(FP)
	I64Load b+8(FP)
	I64Load size+16(FP)
	Call memeqbody<>(SB)
	I64Store8 ret+24(FP)
	RET

// memequal_varlen(a, b unsafe.Pointer) bool
TEXT runtime·memequal_varlen(SB), NOSPLIT, $0-17
	Get SP
	I64Load a+0(FP)
	I64Load b+8(FP)

#define	REGCTXT	R22

// memequal(a, b unsafe.Pointer, size uintptr) bool
TEXT runtime·memequal(SB),NOSPLIT,$0-13
	MOVW	a+0(FP), R1
	MOVW	b+4(FP), R2
	BEQ	R1, R2, eq
	MOVW	size+8(FP), R3
	ADDU	R1, R3, R4
loop:
	BNE	R1, R4, test
	MOVW	$1, R1
	MOVB	R1, ret+12(FP)
	RET
test:
	MOVBU	(R1), R6
	ADDU	$1, R1
	MOVBU	(R2), R7
	ADDU	$1, R2
	BEQ	R6, R7, loop

	MOVB	R0, ret+12(FP)
	RET
eq:
	MOVW	$1, R1

// Defined by the runtime package.
func signal_disable(uint32)
func signal_enable(uint32)
func signal_ignore(uint32)
func signal_ignored(uint32) bool
func signal_recv() uint32

func loop() {
	for {
		process(syscall.Signal(signal_recv()))
	}
}

func init() {
	watchSignalLoop = loop
}

const (
	numSig = 65 // max across all systems
)

func signum(sig os.Signal) int {
	switch sig := sig.(type) {

  // detection graph, disconnecting each loop from the enclosing graph.
  // Specifically, we:
  // * add a new "frame" node for each loop.
  // * replace edges to "Enter" nodes, and edges from "Exit" nodes with edges
  //   to/from the corresponding frame node. In essence, we collapse the loop
  //   into a single node for the purpose of cycle detection in the enclosing
  //   graph.

// Test escape analysis for goto statements.

package escape

var x bool

func f1() {
	var p *int
loop:
	if x {
		goto loop
	}
	// BAD: We should be able to recognize that there
	// aren't any more "goto loop" after here.
	p = new(int) // ERROR "escapes to heap"
	_ = p
}

func f2() {
	var p *int
	if x {
	loop:
		goto loop
	} else {
		p = new(int) // ERROR "does not escape"
	}
	_ = p
}

#include "textflag.h"

#define	REGCTXT	R29

// memequal(a, b unsafe.Pointer, size uintptr) bool
TEXT runtime·memequal<ABIInternal>(SB),NOSPLIT|NOFRAME,$0-25
	BEQ	R4, R5, eq
	ADDV	R4, R6, R7
	PCALIGN	$16
loop:
	BNE	R4, R7, test
	MOVV	$1, R4
	RET
test:
	MOVBU	(R4), R9
	ADDV	$1, R4
	MOVBU	(R5), R10
	ADDV	$1, R5
	BEQ	R9, R10, loop

	MOVB    R0, R4
	RET
eq:
	MOVV	$1, R4
	RET

// Issue #14768 - make sure we can inline for loops.
func for1(fn func() bool) { // ERROR "can inline for1" "fn does not escape"
	for {
		if fn() {
			break
		} else {
			continue
		}
	}
}

func for2(fn func() bool) { // ERROR "can inline for2" "fn does not escape"
Loop:
	for {
		if fn() {
			break Loop
		} else {
			continue Loop
		}
	}
}

// Defined by the runtime package.
func signal_disable(uint32)
func signal_enable(uint32)
func signal_ignore(uint32)
func signal_ignored(uint32) bool
func signal_recv() string

func init() {
	watchSignalLoop = loop
}

func loop() {
	for {
		process(syscall.Note(signal_recv()))
	}
}

const numSig = 256

func signum(sig os.Signal) int {
	switch sig := sig.(type) {