[dev.garbage] runtime: use s.base() everywhere it makes sense

Currently we have lots of (s.start << _PageShift) and variants. We now
have an s.base() function that returns this. It's faster and more
readable, so use it.

Change-Id: I888060a9dae15ea75ca8cc1c2b31c905e71b452b
Reviewed-on: https://go-review.googlesource.com/22559Reviewed-by: Rick Hudson <rlh@golang.org>
Run-TryBot: Austin Clements <austin@google.com>

src/runtime/heapdump.go

@@ -447,7 +447,7 @@ func dumproots() {
 					continue
 				}
 				spf := (*specialfinalizer)(unsafe.Pointer(sp))
-				p := unsafe.Pointer((uintptr(s.start) << _PageShift) + uintptr(spf.special.offset))
+				p := unsafe.Pointer(s.base() + uintptr(spf.special.offset))
 				dumpfinalizer(p, spf.fn, spf.fint, spf.ot)
 			}
 		}
@@ -467,7 +467,7 @@ func dumpobjs() {
 		if s.state != _MSpanInUse {
 			continue
 		}
-		p := uintptr(s.start << _PageShift)
+		p := s.base()
 		size := s.elemsize
 		n := (s.npages << _PageShift) / size
 		if n > uintptr(len(freemark)) {
@@ -619,7 +619,7 @@ func dumpmemprof() {
 				continue
 			}
 			spp := (*specialprofile)(unsafe.Pointer(sp))
-			p := uintptr(s.start<<_PageShift) + uintptr(spp.special.offset)
+			p := s.base() + uintptr(spp.special.offset)
 			dumpint(tagAllocSample)
 			dumpint(uint64(p))
 			dumpint(uint64(uintptr(unsafe.Pointer(spp.b))))

src/runtime/mfinal.go

@@ -402,7 +402,7 @@ func findObject(v unsafe.Pointer) (s *mspan, x unsafe.Pointer, n uintptr) {
 	if s == nil {
 		return
 	}
-	x = unsafe.Pointer(uintptr(s.start) << pageShift)
+	x = unsafe.Pointer(s.base())
 
 	if uintptr(v) < uintptr(x) || uintptr(v) >= uintptr(unsafe.Pointer(s.limit)) || s.state != mSpanInUse {
 		s = nil

src/runtime/mgcmark.go

@@ -1247,7 +1247,7 @@ func gcDumpObject(label string, obj, off uintptr) {
 		print(" s=nil\n")
 		return
 	}
-	print(" s.start*_PageSize=", hex(s.start*_PageSize), " s.limit=", hex(s.limit), " s.sizeclass=", s.sizeclass, " s.elemsize=", s.elemsize, "\n")
+	print(" s.base()=", hex(s.base()), " s.limit=", hex(s.limit), " s.sizeclass=", s.sizeclass, " s.elemsize=", s.elemsize, "\n")
 	skipped := false
 	for i := uintptr(0); i < s.elemsize; i += sys.PtrSize {
 		// For big objects, just print the beginning (because

src/runtime/mheap.go

@@ -808,7 +808,7 @@ func (h *mheap) freeSpanLocked(s *mspan, acctinuse, acctidle bool, unusedsince i
 		}
 	case _MSpanInUse:
 		if s.allocCount != 0 || s.sweepgen != h.sweepgen {
-			print("MHeap_FreeSpanLocked - span ", s, " ptr ", hex(s.start<<_PageShift), " allocCount ", s.allocCount, " sweepgen ", s.sweepgen, "/", h.sweepgen, "\n")
+			print("MHeap_FreeSpanLocked - span ", s, " ptr ", hex(s.base()), " allocCount ", s.allocCount, " sweepgen ", s.sweepgen, "/", h.sweepgen, "\n")
 			throw("MHeap_FreeSpanLocked - invalid free")
 		}
 		h.pagesInUse -= uint64(s.npages)
@@ -892,7 +892,7 @@ func scavengelist(list *mSpanList, now, limit uint64) uintptr {
 	var sumreleased uintptr
 	for s := list.first; s != nil; s = s.next {
 		if (now-uint64(s.unusedsince)) > limit && s.npreleased != s.npages {
-			start := uintptr(s.start) << _PageShift
+			start := s.base()
 			end := start + s.npages<<_PageShift
 			if sys.PhysPageSize > _PageSize {
 				// We can only release pages in
@@ -1062,7 +1062,7 @@ func addspecial(p unsafe.Pointer, s *special) bool {
 	mp := acquirem()
 	span.ensureSwept()
 
-	offset := uintptr(p) - uintptr(span.start<<_PageShift)
+	offset := uintptr(p) - span.base()
 	kind := s.kind
 
 	lock(&span.speciallock)
@@ -1110,7 +1110,7 @@ func removespecial(p unsafe.Pointer, kind uint8) *special {
 	mp := acquirem()
 	span.ensureSwept()
 
-	offset := uintptr(p) - uintptr(span.start<<_PageShift)
+	offset := uintptr(p) - span.base()
 
 	lock(&span.speciallock)
 	t := &span.specials

src/runtime/stack.go

@@ -198,7 +198,7 @@ func stackpoolalloc(order uint8) gclinkptr {
 			throw("bad stackfreelist")
 		}
 		for i := uintptr(0); i < _StackCacheSize; i += _FixedStack << order {
-			x := gclinkptr(uintptr(s.start)<<_PageShift + i)
+			x := gclinkptr(s.base() + i)
 			x.ptr().next = s.stackfreelist
 			s.stackfreelist = x
 		}
@@ -391,7 +391,7 @@ func stackalloc(n uint32) (stack, []stkbar) {
 				throw("out of memory")
 			}
 		}
-		v = unsafe.Pointer(s.start << _PageShift)
+		v = unsafe.Pointer(s.base())
 	}
 
 	if raceenabled {
@@ -456,7 +456,7 @@ func stackfree(stk stack, n uintptr) {
 	} else {
 		s := mheap_.lookup(v)
 		if s.state != _MSpanStack {
-			println(hex(s.start<<_PageShift), v)
+			println(hex(s.base()), v)
 			throw("bad span state")
 		}
 		if gcphase == _GCoff {