runtime: clean up loops over allp

allp now has length gomaxprocs, which means none of allp[i] are nil or
in state _Pdead. This lets replace several different styles of loops
over allp with normal range loops.

for i := 0; i < gomaxprocs; i++ { ... } loops can simply range over
allp. Likewise, range loops over allp[:gomaxprocs] can just range over
allp.

Loops that check for p == nil || p.state == _Pdead don't need to check
this any more.

Loops that check for p == nil don't have to check this *if* dead Ps
don't affect them. I checked that all such loops are, in fact,
unaffected by dead Ps. One loop was potentially affected, which this
fixes by zeroing p.gcAssistTime in procresize.

Updates #15131.

Change-Id: Ifa1c2a86ed59892eca0610360a75bb613bc6dcee
Reviewed-on: https://go-review.googlesource.com/45575
Run-TryBot: Austin Clements <austin@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Rick Hudson <rlh@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

1 files changed, 0 insertions, 6 deletions

diff --git a/src/runtime/trace.go b/src/runtime/trace.go
index 398d0449b4..e179e18b9f 100644
--- a/src/runtime/trace.go
+++ b/src/runtime/trace.go
@@ -280,9 +280,6 @@ func StopTrace() {
 	// Loop over all allocated Ps because dead Ps may still have
 	// trace buffers.
 	for _, p := range allp[:cap(allp)] {
-		if p == nil {
-			break
-		}
 		buf := p.tracebuf
 		if buf != 0 {
 			traceFullQueue(buf)
@@ -323,9 +320,6 @@ func StopTrace() {
 	// The lock protects us from races with StartTrace/StopTrace because they do stop-the-world.
 	lock(&trace.lock)
 	for _, p := range allp[:cap(allp)] {
-		if p == nil {
-			break
-		}
 		if p.tracebuf != 0 {
 			throw("trace: non-empty trace buffer in proc")
 		}