runtime: undo manual inlining of mbits.setMarked

Since atomic.Or8 is now an intrinsic (and has been for some time),
markBits.setMarked is inlinable. Undo the manual inlining of it.

Change-Id: I8e37ccf0851ad1d3088d9c8ae0f6f0c439d7eb2d
Reviewed-on: https://go-review.googlesource.com/c/138659
Run-TryBot: Austin Clements <austin@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

src/runtime/mbitmap.go

@@ -283,9 +283,7 @@ func (m markBits) isMarked() bool {
 	return *m.bytep&m.mask != 0
 }
 
-// setMarked sets the marked bit in the markbits, atomically. Some compilers
-// are not able to inline atomic.Or8 function so if it appears as a hot spot consider
-// inlining it manually.
+// setMarked sets the marked bit in the markbits, atomically.
 func (m markBits) setMarked() {
 	// Might be racing with other updates, so use atomic update always.
 	// We used to be clever here and use a non-atomic update in certain

src/runtime/mgcmark.go

@@ -1228,8 +1228,7 @@ func greyobject(obj, base, off uintptr, span *mspan, gcw *gcWork, objIndex uintp
 		if mbits.isMarked() {
 			return
 		}
-		// mbits.setMarked() // Avoid extra call overhead with manual inlining.
-		atomic.Or8(mbits.bytep, mbits.mask)
+		mbits.setMarked()
 		// If this is a noscan object, fast-track it to black
 		// instead of greying it.
 		if span.spanclass.noscan() {