runtime: use more natural types in struct workbuf

Until recently, struct workbuf had only lfnode and uintptr fields
before the obj array to make it convenient to compute the size of the
obj array.  It slowly grew more fields until this became inconvenient
enough that it was restructured to make the size computation easy.
Now the size computation doesn't care what the field types are, so
switch to more natural types.

Change-Id: I966140ba7ebb4aeb41d5c66d9d2a3bdc17dd4bcf
Reviewed-on: https://go-review.googlesource.com/5262Reviewed-by: Russ Cox <rsc@golang.org>

src/runtime/mgcwork.go

@@ -84,7 +84,7 @@ func (ww *gcWorkProducer) put(obj uintptr) {
 	wbuf.obj[wbuf.nobj] = obj
 	wbuf.nobj++
 
-	if wbuf.nobj == uintptr(len(wbuf.obj)) {
+	if wbuf.nobj == len(wbuf.obj) {
 		putfull(wbuf, 50)
 		w.wbuf = 0
 	}
@@ -199,9 +199,9 @@ func (w *gcWork) balance() {
 
 type workbufhdr struct {
 	node  lfnode // must be first
-	nobj  uintptr
+	nobj  int
 	inuse bool   // This workbuf is in use by some gorotuine and is not on the work.empty/partial/full queues.
-	log   [4]uintptr // line numbers forming a history of ownership changes to workbuf
+	log   [4]int // line numbers forming a history of ownership changes to workbuf
 }
 
 type workbuf struct {
@@ -222,7 +222,7 @@ type workbuf struct {
 
 // logget records the past few values of entry to aid in debugging.
 // logget checks the buffer b is not currently in use.
-func (b *workbuf) logget(entry uintptr) {
+func (b *workbuf) logget(entry int) {
 	if !_Debugwbufs {
 		return
 	}
@@ -239,7 +239,7 @@ func (b *workbuf) logget(entry uintptr) {
 
 // logput records the past few values of entry to aid in debugging.
 // logput checks the buffer b is currently in use.
-func (b *workbuf) logput(entry uintptr) {
+func (b *workbuf) logput(entry int) {
 	if !_Debugwbufs {
 		return
 	}
@@ -283,7 +283,7 @@ func checknocurrentwbuf() {
 // allocating new buffers if none are available.
 // entry is used to record a brief history of ownership.
 //go:nowritebarrier
-func getempty(entry uintptr) *workbuf {
+func getempty(entry int) *workbuf {
 	var b *workbuf
 	if work.empty != 0 {
 		b = (*workbuf)(lfstackpop(&work.empty))
@@ -301,7 +301,7 @@ func getempty(entry uintptr) *workbuf {
 // putempty puts a workbuf onto the work.empty list.
 // Upon entry this go routine owns b. The lfstackpush relinquishes ownership.
 //go:nowritebarrier
-func putempty(b *workbuf, entry uintptr) {
+func putempty(b *workbuf, entry int) {
 	b.checkempty()
 	b.logput(entry)
 	lfstackpush(&work.empty, &b.node)
@@ -311,7 +311,7 @@ func putempty(b *workbuf, entry uintptr) {
 // putfull accepts partially full buffers so the GC can avoid competing
 // with the mutators for ownership of partially full buffers.
 //go:nowritebarrier
-func putfull(b *workbuf, entry uintptr) {
+func putfull(b *workbuf, entry int) {
 	b.checknonempty()
 	b.logput(entry)
 	lfstackpush(&work.full, &b.node)
@@ -323,7 +323,7 @@ func putfull(b *workbuf, entry uintptr) {
 // using entry + xxx00000 to
 // indicating that two line numbers in the call chain.
 //go:nowritebarrier
-func getpartialorempty(entry uintptr) *workbuf {
+func getpartialorempty(entry int) *workbuf {
 	var b *workbuf
 	// If this m has a buf in currentwbuf then as an optimization
 	// simply return that buffer. If it turns out currentwbuf
@@ -332,7 +332,7 @@ func getpartialorempty(entry uintptr) *workbuf {
 	if getg().m.currentwbuf != 0 {
 		b = (*workbuf)(unsafe.Pointer(xchguintptr(&getg().m.currentwbuf, 0)))
 		if b != nil {
-			if b.nobj <= uintptr(len(b.obj)) {
+			if b.nobj <= len(b.obj) {
 				return b
 			}
 			putfull(b, entry+80100000)
@@ -357,13 +357,13 @@ func getpartialorempty(entry uintptr) *workbuf {
 // using entry + xxx00000 to
 // indicating that two call chain line numbers.
 //go:nowritebarrier
-func putpartial(b *workbuf, entry uintptr) {
+func putpartial(b *workbuf, entry int) {
 	if b.nobj == 0 {
 		putempty(b, entry+81500000)
-	} else if b.nobj < uintptr(len(b.obj)) {
+	} else if b.nobj < len(b.obj) {
 		b.logput(entry)
 		lfstackpush(&work.partial, &b.node)
-	} else if b.nobj == uintptr(len(b.obj)) {
+	} else if b.nobj == len(b.obj) {
 		b.logput(entry)
 		lfstackpush(&work.full, &b.node)
 	} else {
@@ -374,7 +374,7 @@ func putpartial(b *workbuf, entry uintptr) {
 // trygetfull tries to get a full or partially empty workbuffer.
 // If one is not immediately available return nil
 //go:nowritebarrier
-func trygetfull(entry uintptr) *workbuf {
+func trygetfull(entry int) *workbuf {
 	b := (*workbuf)(lfstackpop(&work.full))
 	if b == nil {
 		b = (*workbuf)(lfstackpop(&work.partial))
@@ -415,7 +415,7 @@ func trygetfull(entry uintptr) *workbuf {
 // This is in fact the termination condition for the STW mark
 // phase.
 //go:nowritebarrier
-func getfull(entry uintptr) *workbuf {
+func getfull(entry int) *workbuf {
 	b := (*workbuf)(lfstackpop(&work.full))
 	if b != nil {
 		b.logget(entry)
@@ -480,7 +480,7 @@ func handoff(b *workbuf) *workbuf {
 	n := b.nobj / 2
 	b.nobj -= n
 	b1.nobj = n
-	memmove(unsafe.Pointer(&b1.obj[0]), unsafe.Pointer(&b.obj[b.nobj]), n*unsafe.Sizeof(b1.obj[0]))
+	memmove(unsafe.Pointer(&b1.obj[0]), unsafe.Pointer(&b.obj[b.nobj]), uintptr(n)*unsafe.Sizeof(b1.obj[0]))
 	_g_ := getg()
 	_g_.m.gcstats.nhandoff++
 	_g_.m.gcstats.nhandoffcnt += uint64(n)