internal,runtime: use the builtin clear

To simplify the code.

Change-Id: I023de705504c0b580718eec3c7c563b6cf2c8184
GitHub-Last-Rev: 026b32c799b13d0c7ded54f2e61429e6c5ed0aa8
GitHub-Pull-Request: golang/go#73412
Reviewed-on: https://go-review.googlesource.com/c/go/+/666118
Reviewed-by: Keith Randall <khr@golang.org>
Reviewed-by: Keith Randall <khr@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Auto-Submit: Keith Randall <khr@golang.org>
Reviewed-by: Michael Pratt <mpratt@google.com>

src/internal/profile/graph.go

@@ -253,12 +253,8 @@ func NewGraph(prof *Profile, o *Options) *Graph {
 		if dw == 0 && w == 0 {
 			continue
 		}
-		for k := range seenNode {
-			delete(seenNode, k)
-		}
-		for k := range seenEdge {
-			delete(seenEdge, k)
-		}
+		clear(seenNode)
+		clear(seenEdge)
 		var parent *Node
 		// A residual edge goes over one or more nodes that were not kept.
 		residual := false

src/internal/zstd/xxhash.go

@@ -41,9 +41,7 @@ func (xh *xxhash64) reset() {
 	xh.v[3] = xxhPrime64c1
 	xh.v[3] = -xh.v[3]
 
-	for i := range xh.buf {
-		xh.buf[i] = 0
-	}
+	clear(xh.buf[:])
 	xh.cnt = 0
 }
 

src/runtime/mstats.go

@@ -834,9 +834,7 @@ func (m *consistentHeapStats) unsafeRead(out *heapStatsDelta) {
 func (m *consistentHeapStats) unsafeClear() {
 	assertWorldStopped()
 
-	for i := range m.stats {
-		m.stats[i] = heapStatsDelta{}
-	}
+	clear(m.stats[:])
 }
 
 // read takes a globally consistent snapshot of m

src/runtime/proc.go

@@ -5690,14 +5690,10 @@ func (pp *p) destroy() {
 		wbBufFlush1(pp)
 		pp.gcw.dispose()
 	}
-	for i := range pp.sudogbuf {
-		pp.sudogbuf[i] = nil
-	}
+	clear(pp.sudogbuf[:])
 	pp.sudogcache = pp.sudogbuf[:0]
 	pp.pinnerCache = nil
-	for j := range pp.deferpoolbuf {
-		pp.deferpoolbuf[j] = nil
-	}
+	clear(pp.deferpoolbuf[:])
 	pp.deferpool = pp.deferpoolbuf[:0]
 	systemstack(func() {
 		for i := 0; i < pp.mspancache.len; i++ {