runtime: remove wbufptr

Since workbuf is now marked go:notinheap, the write barrier-preventing
wrapper type wbufptr is no longer necessary. Remove it.

Change-Id: I3e5b5803a1547d65de1c1a9c22458a38e08549b7
Reviewed-on: https://go-review.googlesource.com/35971
Run-TryBot: Austin Clements <austin@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Rick Hudson <rlh@golang.org>

src/runtime/mgcwork.go

@@ -25,21 +25,6 @@ const (
 // grey objects, thus blackening them, and then scans them,
 // potentially producing new pointers to grey objects.
 
-// A wbufptr holds a workbuf*, but protects it from write barriers.
-// workbufs never live on the heap, so write barriers are unnecessary.
-// Write barriers on workbuf pointers may also be dangerous in the GC.
-//
-// TODO: Since workbuf is now go:notinheap, this isn't necessary.
-type wbufptr uintptr
-
-func wbufptrOf(w *workbuf) wbufptr {
-	return wbufptr(unsafe.Pointer(w))
-}
-
-func (wp wbufptr) ptr() *workbuf {
-	return (*workbuf)(unsafe.Pointer(wp))
-}
-
 // A gcWork provides the interface to produce and consume work for the
 // garbage collector.
 //
@@ -75,7 +60,7 @@ type gcWork struct {
 	// next.
 	//
 	// Invariant: Both wbuf1 and wbuf2 are nil or neither are.
-	wbuf1, wbuf2 wbufptr
+	wbuf1, wbuf2 *workbuf
 
 	// Bytes marked (blackened) on this gcWork. This is aggregated
 	// into work.bytesMarked by dispose.
@@ -87,12 +72,12 @@ type gcWork struct {
 }
 
 func (w *gcWork) init() {
-	w.wbuf1 = wbufptrOf(getempty())
+	w.wbuf1 = getempty()
 	wbuf2 := trygetfull()
 	if wbuf2 == nil {
 		wbuf2 = getempty()
 	}
-	w.wbuf2 = wbufptrOf(wbuf2)
+	w.wbuf2 = wbuf2
 }
 
 // put enqueues a pointer for the garbage collector to trace.
@@ -100,18 +85,18 @@ func (w *gcWork) init() {
 //go:nowritebarrier
 func (w *gcWork) put(obj uintptr) {
 	flushed := false
-	wbuf := w.wbuf1.ptr()
+	wbuf := w.wbuf1
 	if wbuf == nil {
 		w.init()
-		wbuf = w.wbuf1.ptr()
+		wbuf = w.wbuf1
 		// wbuf is empty at this point.
 	} else if wbuf.nobj == len(wbuf.obj) {
 		w.wbuf1, w.wbuf2 = w.wbuf2, w.wbuf1
-		wbuf = w.wbuf1.ptr()
+		wbuf = w.wbuf1
 		if wbuf.nobj == len(wbuf.obj) {
 			putfull(wbuf)
 			wbuf = getempty()
-			w.wbuf1 = wbufptrOf(wbuf)
+			w.wbuf1 = wbuf
 			flushed = true
 		}
 	}
@@ -132,7 +117,7 @@ func (w *gcWork) put(obj uintptr) {
 // otherwise it returns false and the caller needs to call put.
 //go:nowritebarrier
 func (w *gcWork) putFast(obj uintptr) bool {
-	wbuf := w.wbuf1.ptr()
+	wbuf := w.wbuf1
 	if wbuf == nil {
 		return false
 	} else if wbuf.nobj == len(wbuf.obj) {
@@ -151,15 +136,15 @@ func (w *gcWork) putFast(obj uintptr) bool {
 // other gcWork instances or other caches.
 //go:nowritebarrier
 func (w *gcWork) tryGet() uintptr {
-	wbuf := w.wbuf1.ptr()
+	wbuf := w.wbuf1
 	if wbuf == nil {
 		w.init()
-		wbuf = w.wbuf1.ptr()
+		wbuf = w.wbuf1
 		// wbuf is empty at this point.
 	}
 	if wbuf.nobj == 0 {
 		w.wbuf1, w.wbuf2 = w.wbuf2, w.wbuf1
-		wbuf = w.wbuf1.ptr()
+		wbuf = w.wbuf1
 		if wbuf.nobj == 0 {
 			owbuf := wbuf
 			wbuf = trygetfull()
@@ -167,7 +152,7 @@ func (w *gcWork) tryGet() uintptr {
 				return 0
 			}
 			putempty(owbuf)
-			w.wbuf1 = wbufptrOf(wbuf)
+			w.wbuf1 = wbuf
 		}
 	}
 
@@ -180,7 +165,7 @@ func (w *gcWork) tryGet() uintptr {
 // the caller is expected to call tryGet().
 //go:nowritebarrier
 func (w *gcWork) tryGetFast() uintptr {
-	wbuf := w.wbuf1.ptr()
+	wbuf := w.wbuf1
 	if wbuf == nil {
 		return 0
 	}
@@ -197,15 +182,15 @@ func (w *gcWork) tryGetFast() uintptr {
 // been retrieved.  get returns 0 if there are no pointers remaining.
 //go:nowritebarrier
 func (w *gcWork) get() uintptr {
-	wbuf := w.wbuf1.ptr()
+	wbuf := w.wbuf1
 	if wbuf == nil {
 		w.init()
-		wbuf = w.wbuf1.ptr()
+		wbuf = w.wbuf1
 		// wbuf is empty at this point.
 	}
 	if wbuf.nobj == 0 {
 		w.wbuf1, w.wbuf2 = w.wbuf2, w.wbuf1
-		wbuf = w.wbuf1.ptr()
+		wbuf = w.wbuf1
 		if wbuf.nobj == 0 {
 			owbuf := wbuf
 			wbuf = getfull()
@@ -213,7 +198,7 @@ func (w *gcWork) get() uintptr {
 				return 0
 			}
 			putempty(owbuf)
-			w.wbuf1 = wbufptrOf(wbuf)
+			w.wbuf1 = wbuf
 		}
 	}
 
@@ -231,21 +216,21 @@ func (w *gcWork) get() uintptr {
 //
 //go:nowritebarrier
 func (w *gcWork) dispose() {
-	if wbuf := w.wbuf1.ptr(); wbuf != nil {
+	if wbuf := w.wbuf1; wbuf != nil {
 		if wbuf.nobj == 0 {
 			putempty(wbuf)
 		} else {
 			putfull(wbuf)
 		}
-		w.wbuf1 = 0
+		w.wbuf1 = nil
 
-		wbuf = w.wbuf2.ptr()
+		wbuf = w.wbuf2
 		if wbuf.nobj == 0 {
 			putempty(wbuf)
 		} else {
 			putfull(wbuf)
 		}
-		w.wbuf2 = 0
+		w.wbuf2 = nil
 	}
 	if w.bytesMarked != 0 {
 		// dispose happens relatively infrequently. If this
@@ -265,14 +250,14 @@ func (w *gcWork) dispose() {
 // global queue.
 //go:nowritebarrier
 func (w *gcWork) balance() {
-	if w.wbuf1 == 0 {
+	if w.wbuf1 == nil {
 		return
 	}
-	if wbuf := w.wbuf2.ptr(); wbuf.nobj != 0 {
+	if wbuf := w.wbuf2; wbuf.nobj != 0 {
 		putfull(wbuf)
-		w.wbuf2 = wbufptrOf(getempty())
-	} else if wbuf := w.wbuf1.ptr(); wbuf.nobj > 4 {
-		w.wbuf1 = wbufptrOf(handoff(wbuf))
+		w.wbuf2 = getempty()
+	} else if wbuf := w.wbuf1; wbuf.nobj > 4 {
+		w.wbuf1 = handoff(wbuf)
 	} else {
 		return
 	}
@@ -285,7 +270,7 @@ func (w *gcWork) balance() {
 // empty returns true if w has no mark work available.
 //go:nowritebarrier
 func (w *gcWork) empty() bool {
-	return w.wbuf1 == 0 || (w.wbuf1.ptr().nobj == 0 && w.wbuf2.ptr().nobj == 0)
+	return w.wbuf1 == nil || (w.wbuf1.nobj == 0 && w.wbuf2.nobj == 0)
 }
 
 // Internally, the GC work pool is kept in arrays in work buffers.