runtime: update a few comments

noescape is now 0 instructions with the SSA backend.
fast atomics are no longer a TODO (at least for amd64).

Change-Id: Ib6e06f7471bef282a47ba236d8ce95404bb60a42
Reviewed-on: https://go-review.googlesource.com/28087
Run-TryBot: Keith Randall <khr@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Reviewed-by: Cherry Zhang <cherryyz@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>

src/runtime/proc.go

@@ -543,7 +543,7 @@ func ready(gp *g, traceskip int, next bool) {
 	// status is Gwaiting or Gscanwaiting, make Grunnable and put on runq
 	casgstatus(gp, _Gwaiting, _Grunnable)
 	runqput(_g_.m.p.ptr(), gp, next)
-	if atomic.Load(&sched.npidle) != 0 && atomic.Load(&sched.nmspinning) == 0 { // TODO: fast atomic
+	if atomic.Load(&sched.npidle) != 0 && atomic.Load(&sched.nmspinning) == 0 {
 		wakep()
 	}
 	_g_.m.locks--
@@ -1901,7 +1901,7 @@ top:
 	// If number of spinning M's >= number of busy P's, block.
 	// This is necessary to prevent excessive CPU consumption
 	// when GOMAXPROCS>>1 but the program parallelism is low.
-	if !_g_.m.spinning && 2*atomic.Load(&sched.nmspinning) >= procs-atomic.Load(&sched.npidle) { // TODO: fast atomic
+	if !_g_.m.spinning && 2*atomic.Load(&sched.nmspinning) >= procs-atomic.Load(&sched.npidle) {
 		goto stop
 	}
 	if !_g_.m.spinning {
@@ -2341,7 +2341,7 @@ func reentersyscall(pc, sp uintptr) {
 		save(pc, sp)
 	}
 
-	if atomic.Load(&sched.sysmonwait) != 0 { // TODO: fast atomic
+	if atomic.Load(&sched.sysmonwait) != 0 {
 		systemstack(entersyscall_sysmon)
 		save(pc, sp)
 	}
@@ -2806,7 +2806,7 @@ func newproc1(fn *funcval, argp *uint8, narg int32, nret int32, callerpc uintptr
 	}
 	runqput(_p_, newg, true)
 
-	if atomic.Load(&sched.npidle) != 0 && atomic.Load(&sched.nmspinning) == 0 && unsafe.Pointer(fn.fn) != unsafe.Pointer(funcPC(main)) { // TODO: fast atomic
+	if atomic.Load(&sched.npidle) != 0 && atomic.Load(&sched.nmspinning) == 0 && unsafe.Pointer(fn.fn) != unsafe.Pointer(funcPC(main)) {
 		wakep()
 	}
 	_g_.m.locks--
@@ -3604,7 +3604,7 @@ func sysmon() {
 			delay = 10 * 1000
 		}
 		usleep(delay)
-		if debug.schedtrace <= 0 && (sched.gcwaiting != 0 || atomic.Load(&sched.npidle) == uint32(gomaxprocs)) { // TODO: fast atomic
+		if debug.schedtrace <= 0 && (sched.gcwaiting != 0 || atomic.Load(&sched.npidle) == uint32(gomaxprocs)) {
 			lock(&sched.lock)
 			if atomic.Load(&sched.gcwaiting) != 0 || atomic.Load(&sched.npidle) == uint32(gomaxprocs) {
 				atomic.Store(&sched.sysmonwait, 1)

src/runtime/stubs.go

@@ -90,7 +90,7 @@ func memequal(a, b unsafe.Pointer, size uintptr) bool
 // noescape hides a pointer from escape analysis.  noescape is
 // the identity function but escape analysis doesn't think the
 // output depends on the input.  noescape is inlined and currently
-// compiles down to a single xor instruction.
+// compiles down to zero instructions.
 // USE CAREFULLY!
 //go:nosplit
 func noescape(p unsafe.Pointer) unsafe.Pointer {