runtime: use built-in clear to simplify code

Change-Id: Icb6d9ca996b4119d8636d9f7f6a56e510d74d059
GitHub-Last-Rev: 08178e8ff7
GitHub-Pull-Request: golang/go#66188
Reviewed-on: https://go-review.googlesource.com/c/go/+/569979
Reviewed-by: Keith Randall <khr@golang.org>
Reviewed-by: qiulaidongfeng <2645477756@qq.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Michael Knyszek <mknyszek@google.com>
Auto-Submit: Keith Randall <khr@golang.org>
Reviewed-by: Keith Randall <khr@google.com>

src/runtime/heapdump.go

@@ -735,9 +735,7 @@ func makeheapobjbv(p uintptr, size uintptr) bitvector {
 		tmpbuf = (*[1 << 30]byte)(p)[:n]
 	}
 	// Convert heap bitmap to pointer bitmap.
-	for i := uintptr(0); i < nptr/8+1; i++ {
-		tmpbuf[i] = 0
-	}
+	clear(tmpbuf[:nptr/8+1])
 	if goexperiment.AllocHeaders {
 		s := spanOf(p)
 		tp := s.typePointersOf(p, size)

src/runtime/mcheckmark.go

@@ -52,9 +52,7 @@ func startCheckmarks() {
 			arena.checkmarks = bitmap
 		} else {
 			// Otherwise clear the existing bitmap.
-			for i := range bitmap.b {
-				bitmap.b[i] = 0
-			}
+			clear(bitmap.b[:])
 		}
 	}
 	// Enable checkmarking.

src/runtime/mgc.go

@@ -1665,9 +1665,7 @@ func gcResetMarkState() {
 	unlock(&mheap_.lock)
 	for _, ai := range arenas {
 		ha := mheap_.arenas[ai.l1()][ai.l2()]
-		for i := range ha.pageMarks {
-			ha.pageMarks[i] = 0
-		}
+		clear(ha.pageMarks[:])
 	}
 
 	work.bytesMarked = 0

src/runtime/mpagealloc.go

@@ -511,10 +511,7 @@ func (p *pageAlloc) update(base, npages uintptr, contig, alloc bool) {
 		// either totally allocated or freed.
 		whole := p.summary[len(p.summary)-1][sc+1 : ec]
 		if alloc {
-			// Should optimize into a memclr.
-			for i := range whole {
-				whole[i] = 0
-			}
+			clear(whole)
 		} else {
 			for i := range whole {
 				whole[i] = freeChunkSum

src/runtime/mpallocbits.go

@@ -85,18 +85,14 @@ func (b *pageBits) clearRange(i, n uint) {
 	_ = b[j/64]
 	// Clear leading bits.
 	b[i/64] &^= ^uint64(0) << (i % 64)
-	for k := i/64 + 1; k < j/64; k++ {
-		b[k] = 0
-	}
+	clear(b[i/64+1 : j/64])
 	// Clear trailing bits.
 	b[j/64] &^= (uint64(1) << (j%64 + 1)) - 1
 }
 
 // clearAll frees all the bits of b.
 func (b *pageBits) clearAll() {
-	for i := range b {
-		b[i] = 0
-	}
+	clear(b[:])
 }
 
 // clearBlock64 clears the 64-bit aligned block of bits containing the i'th bit that

src/runtime/mprof.go

@@ -954,9 +954,7 @@ func record(r *MemProfileRecord, b *bucket) {
 		asanwrite(unsafe.Pointer(&r.Stack0[0]), unsafe.Sizeof(r.Stack0))
 	}
 	copy(r.Stack0[:], b.stk())
-	for i := int(b.nstk); i < len(r.Stack0); i++ {
-		r.Stack0[i] = 0
-	}
+	clear(r.Stack0[b.nstk:])
 }
 
 func iterate_memprof(fn func(*bucket, uintptr, *uintptr, uintptr, uintptr, uintptr)) {
@@ -1012,9 +1010,7 @@ func BlockProfile(p []BlockProfileRecord) (n int, ok bool) {
 				asanwrite(unsafe.Pointer(&r.Stack0[0]), unsafe.Sizeof(r.Stack0))
 			}
 			i := copy(r.Stack0[:], b.stk())
-			for ; i < len(r.Stack0); i++ {
-				r.Stack0[i] = 0
-			}
+			clear(r.Stack0[i:])
 			p = p[1:]
 		}
 	}
@@ -1042,9 +1038,7 @@ func MutexProfile(p []BlockProfileRecord) (n int, ok bool) {
 			r.Count = int64(bp.count)
 			r.Cycles = bp.cycles
 			i := copy(r.Stack0[:], b.stk())
-			for ; i < len(r.Stack0); i++ {
-				r.Stack0[i] = 0
-			}
+			clear(r.Stack0[i:])
 			p = p[1:]
 		}
 	}

src/runtime/profbuf.go

@@ -367,10 +367,8 @@ func (b *profBuf) write(tagPtr *unsafe.Pointer, now int64, hdr []uint64, stk []u
 	data[0] = uint64(2 + b.hdrsize + uintptr(len(stk))) // length
 	data[1] = uint64(now)                               // time stamp
 	// header, zero-padded
-	i := uintptr(copy(data[2:2+b.hdrsize], hdr))
-	for ; i < b.hdrsize; i++ {
-		data[2+i] = 0
-	}
+	i := copy(data[2:2+b.hdrsize], hdr)
+	clear(data[2+i : 2+b.hdrsize])
 	for i, pc := range stk {
 		data[2+b.hdrsize+uintptr(i)] = uint64(pc)
 	}
@@ -469,9 +467,7 @@ Read:
 			dst := b.overflowBuf
 			dst[0] = uint64(2 + b.hdrsize + 1)
 			dst[1] = time
-			for i := uintptr(0); i < b.hdrsize; i++ {
-				dst[2+i] = 0
-			}
+			clear(dst[2 : 2+b.hdrsize])
 			dst[2+b.hdrsize] = uint64(count)
 			return dst[:2+b.hdrsize+1], overflowTag[:1], false
 		}