runtime: clean up more traces of the old mark bit

Commit 59877bfa renamed bitMarked to bitScan, since the bitmap is no
longer used for marking. However, there were several other references
to this strewn about comments and in some other constant names. Fix
these up, too.

Change-Id: I4183d28c6b01977f1d75a99ad55b150f2211772d
Reviewed-on: https://go-review.googlesource.com/28450
Run-TryBot: Austin Clements <austin@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Rick Hudson <rlh@golang.org>

src/runtime/mbitmap.go

@@ -80,11 +80,11 @@ const (
 	bitPointer = 1 << 0
 	bitScan    = 1 << 4
 
-	heapBitsShift   = 1                     // shift offset between successive bitPointer or bitMarked entries
+	heapBitsShift   = 1                     // shift offset between successive bitPointer or bitScan entries
 	heapBitmapScale = sys.PtrSize * (8 / 2) // number of data bytes described by one heap bitmap byte
 
-	// all mark/pointer bits in a byte
-	bitMarkedAll  = bitScan | bitScan<<heapBitsShift | bitScan<<(2*heapBitsShift) | bitScan<<(3*heapBitsShift)
+	// all scan/pointer bits in a byte
+	bitScanAll    = bitScan | bitScan<<heapBitsShift | bitScan<<(2*heapBitsShift) | bitScan<<(3*heapBitsShift)
 	bitPointerAll = bitPointer | bitPointer<<heapBitsShift | bitPointer<<(2*heapBitsShift) | bitPointer<<(3*heapBitsShift)
 )
 
@@ -481,7 +481,7 @@ func (h heapBits) forward(n uintptr) heapBits {
 	return heapBits{subtractb(h.bitp, n/4), uint32(n%4) * heapBitsShift}
 }
 
-// The caller can test isMarked and isPointer by &-ing with bitMarked and bitPointer.
+// The caller can test morePointers and isPointer by &-ing with bitScan and bitPointer.
 // The result includes in its higher bits the bits for subsequent words
 // described by the same bitmap byte.
 func (h heapBits) bits() uint32 {
@@ -730,7 +730,7 @@ func (h heapBits) initSpan(s *mspan) {
 		end := h.bitp
 		bitp := subtractb(end, nbyte-1)
 		for {
-			*bitp = bitPointerAll | bitMarkedAll
+			*bitp = bitPointerAll | bitScanAll
 			if bitp == end {
 				break
 			}
@@ -945,7 +945,7 @@ func heapBitsSetType(x, size, dataSize uintptr, typ *_type) {
 		b := uint32(*ptrmask)
 		hb := (b & 3) | bitScan
 		if gcphase == _GCoff {
-			// bitPointer == 1, bitMarked is 1 << 4, heapBitsShift is 1.
+			// bitPointer == 1, bitScan is 1 << 4, heapBitsShift is 1.
 			// 110011 is shifted h.shift and complemented.
 			// This clears out the bits that are about to be
 			// ored into *h.hbitp in the next instructions.
@@ -1128,7 +1128,7 @@ func heapBitsSetType(x, size, dataSize uintptr, typ *_type) {
 
 	// Phase 1: Special case for leading byte (shift==0) or half-byte (shift==4).
 	// The leading byte is special because it contains the bits for word 1,
-	// which does not have the marked bits set.
+	// which does not have the scan bit set.
 	// The leading half-byte is special because it's a half a byte and must be
 	// manipulated atomically.
 	switch {
@@ -1177,7 +1177,7 @@ func heapBitsSetType(x, size, dataSize uintptr, typ *_type) {
 		hb |= bitScan << (2 * heapBitsShift)
 		b >>= 2
 		nb -= 2
-		// Note: no bitMarker for second word because that's
+		// Note: no bitScan for second word because that's
 		// the checkmark.
 		if gcphase == _GCoff {
 			*hbitp &^= uint8((bitPointer | bitScan | (bitPointer << heapBitsShift)) << (2 * heapBitsShift))
@@ -1211,7 +1211,7 @@ func heapBitsSetType(x, size, dataSize uintptr, typ *_type) {
 		// but we'll stop at the break and then truncate
 		// appropriately in Phase 3.
 		hb = b & bitPointerAll
-		hb |= bitMarkedAll
+		hb |= bitScanAll
 		if w += 4; w >= nw {
 			break
 		}
@@ -1259,7 +1259,7 @@ func heapBitsSetType(x, size, dataSize uintptr, typ *_type) {
 
 		// Emit bitmap byte.
 		hb = b & bitPointerAll
-		hb |= bitMarkedAll
+		hb |= bitScanAll
 		if w += 4; w >= nw {
 			break
 		}
@@ -1275,7 +1275,7 @@ Phase3:
 		// there are more entries than possible pointer slots.
 		// Discard the excess entries (can't be more than 3).
 		mask := uintptr(1)<<(4-(w-nw)) - 1
-		hb &= mask | mask<<4 // apply mask to both pointer bits and mark bits
+		hb &= mask | mask<<4 // apply mask to both pointer bits and scan bits
 	}
 
 	// Change nw from counting possibly-pointer words to total words in allocation.
@@ -1525,11 +1525,11 @@ Run:
 				dst = add1(dst)
 				bits >>= 8
 			} else {
-				v := bits&bitPointerAll | bitMarkedAll
+				v := bits&bitPointerAll | bitScanAll
 				*dst = uint8(v)
 				dst = subtract1(dst)
 				bits >>= 4
-				v = bits&bitPointerAll | bitMarkedAll
+				v = bits&bitPointerAll | bitScanAll
 				*dst = uint8(v)
 				dst = subtract1(dst)
 				bits >>= 4
@@ -1563,11 +1563,11 @@ Run:
 					dst = add1(dst)
 					bits >>= 8
 				} else {
-					v := bits&0xf | bitMarkedAll
+					v := bits&0xf | bitScanAll
 					*dst = uint8(v)
 					dst = subtract1(dst)
 					bits >>= 4
-					v = bits&0xf | bitMarkedAll
+					v = bits&0xf | bitScanAll
 					*dst = uint8(v)
 					dst = subtract1(dst)
 					bits >>= 4
@@ -1694,7 +1694,7 @@ Run:
 					}
 				} else {
 					for nbits >= 4 {
-						*dst = uint8(bits&0xf | bitMarkedAll)
+						*dst = uint8(bits&0xf | bitScanAll)
 						dst = subtract1(dst)
 						bits >>= 4
 						nbits -= 4
@@ -1752,7 +1752,7 @@ Run:
 			for i := c / 4; i > 0; i-- {
 				bits |= (uintptr(*src) & 0xf) << nbits
 				src = subtract1(src)
-				*dst = uint8(bits&0xf | bitMarkedAll)
+				*dst = uint8(bits&0xf | bitScanAll)
 				dst = subtract1(dst)
 				bits >>= 4
 			}
@@ -1778,7 +1778,7 @@ Run:
 		totalBits = (uintptr(unsafe.Pointer(dstStart))-uintptr(unsafe.Pointer(dst)))*4 + nbits
 		nbits += -nbits & 3
 		for ; nbits > 0; nbits -= 4 {
-			v := bits&0xf | bitMarkedAll
+			v := bits&0xf | bitScanAll
 			*dst = uint8(v)
 			dst = subtract1(dst)
 			bits >>= 4