all: make use of builtin clear

Change-Id: I1df0685c75fc1044ba46003a69ecc7dfc53bbc2b
Reviewed-on: https://go-review.googlesource.com/c/go/+/574675
Reviewed-by: Ian Lance Taylor <iant@google.com>
Reviewed-by: Than McIntosh <thanm@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Auto-Submit: Ian Lance Taylor <iant@google.com>

src/archive/zip/reader_test.go

@@ -904,9 +904,7 @@ func returnRecursiveZip() (r io.ReaderAt, size int64) {
 //	type zeros struct{}
 //
 //	func (zeros) Read(b []byte) (int, error) {
-//		for i := range b {
-//			b[i] = 0
-//		}
+//		clear(b)
 //		return len(b), nil
 //	}
 //

src/archive/zip/zip_test.go

@@ -814,8 +814,6 @@ func TestSuffixSaver(t *testing.T) {
 type zeros struct{}
 
 func (zeros) Read(p []byte) (int, error) {
-	for i := range p {
-		p[i] = 0
-	}
+	clear(p)
 	return len(p), nil
 }

src/crypto/aes/aes_gcm.go

@@ -176,9 +176,7 @@ func (g *gcmAsm) Open(dst, nonce, ciphertext, data []byte) ([]byte, error) {
 	gcmAesFinish(&g.productTable, &tagMask, &expectedTag, uint64(len(ciphertext)), uint64(len(data)))
 
 	if subtle.ConstantTimeCompare(expectedTag[:g.tagSize], tag) != 1 {
-		for i := range out {
-			out[i] = 0
-		}
+		clear(out)
 		return nil, errOpen
 	}
 

src/crypto/aes/gcm_ppc64x.go

@@ -212,9 +212,7 @@ func (g *gcmAsm) Open(dst, nonce, ciphertext, data []byte) ([]byte, error) {
 	ret, out := sliceForAppend(dst, len(ciphertext))
 
 	if subtle.ConstantTimeCompare(expectedTag[:g.tagSize], tag) != 1 {
-		for i := range out {
-			out[i] = 0
-		}
+		clear(out)
 		return nil, errOpen
 	}
 

src/crypto/aes/gcm_s390x.go

@@ -271,9 +271,7 @@ func (g *gcmAsm) Open(dst, nonce, ciphertext, data []byte) ([]byte, error) {
 		// so overwrites dst in the event of a tag mismatch. That
 		// behavior is mimicked here in order to be consistent across
 		// platforms.
-		for i := range out {
-			out[i] = 0
-		}
+		clear(out)
 		return nil, errOpen
 	}
 
@@ -363,9 +361,7 @@ func (g *gcmKMA) Open(dst, nonce, ciphertext, data []byte) ([]byte, error) {
 		// so overwrites dst in the event of a tag mismatch. That
 		// behavior is mimicked here in order to be consistent across
 		// platforms.
-		for i := range out {
-			out[i] = 0
-		}
+		clear(out)
 		return nil, errOpen
 	}
 

src/crypto/cipher/gcm.go

@@ -234,9 +234,7 @@ func (g *gcm) Open(dst, nonce, ciphertext, data []byte) ([]byte, error) {
 		// so overwrites dst in the event of a tag mismatch. That
 		// behavior is mimicked here in order to be consistent across
 		// platforms.
-		for i := range out {
-			out[i] = 0
-		}
+		clear(out)
 		return nil, errOpen
 	}
 

src/crypto/ecdh/ecdh_test.go

@@ -412,9 +412,7 @@ type zr struct{}
 
 // Read replaces the contents of dst with zeros. It is safe for concurrent use.
 func (zr) Read(dst []byte) (n int, err error) {
-	for i := range dst {
-		dst[i] = 0
-	}
+	clear(dst)
 	return len(dst), nil
 }
 

src/crypto/ecdsa/ecdsa.go

@@ -457,9 +457,7 @@ var zeroReader = zr{}
 
 // Read replaces the contents of dst with zeros. It is safe for concurrent use.
 func (zr) Read(dst []byte) (n int, err error) {
-	for i := range dst {
-		dst[i] = 0
-	}
+	clear(dst)
 	return len(dst), nil
 }
 

src/crypto/ed25519/ed25519_test.go

@@ -45,9 +45,7 @@ func Example_ed25519ctx() {
 type zeroReader struct{}
 
 func (zeroReader) Read(buf []byte) (int, error) {
-	for i := range buf {
-		buf[i] = 0
-	}
+	clear(buf)
 	return len(buf), nil
 }
 

src/crypto/internal/bigmod/nat.go

@@ -76,9 +76,7 @@ func (x *Nat) expand(n int) *Nat {
 		return x
 	}
 	extraLimbs := x.limbs[len(x.limbs):n]
-	for i := range extraLimbs {
-		extraLimbs[i] = 0
-	}
+	clear(extraLimbs)
 	x.limbs = x.limbs[:n]
 	return x
 }
@@ -89,9 +87,7 @@ func (x *Nat) reset(n int) *Nat {
 		x.limbs = make([]uint, n)
 		return x
 	}
-	for i := range x.limbs {
-		x.limbs[i] = 0
-	}
+	clear(x.limbs)
 	x.limbs = x.limbs[:n]
 	return x
 }

src/crypto/tls/example_test.go

@@ -18,10 +18,7 @@ import (
 type zeroSource struct{}
 
 func (zeroSource) Read(b []byte) (n int, err error) {
-	for i := range b {
-		b[i] = 0
-	}
-
+	clear(b)
 	return len(b), nil
 }
 

src/crypto/tls/handshake_test.go

@@ -310,10 +310,7 @@ Dialing:
 type zeroSource struct{}
 
 func (zeroSource) Read(b []byte) (n int, err error) {
-	for i := range b {
-		b[i] = 0
-	}
-
+	clear(b)
 	return len(b), nil
 }
 

src/hash/maphash/smhasher_test.go

@@ -318,9 +318,7 @@ type bytesKey struct {
 }
 
 func (k *bytesKey) clear() {
-	for i := range k.b {
-		k.b[i] = 0
-	}
+	clear(k.b)
 }
 func (k *bytesKey) random(r *rand.Rand) {
 	randBytes(r, k.b)

src/internal/fuzz/coverage.go

@@ -13,9 +13,7 @@ import (
 // source code to 0.
 func ResetCoverage() {
 	cov := coverage()
-	for i := range cov {
-		cov[i] = 0
-	}
+	clear(cov)
 }
 
 // SnapshotCoverage copies the current counter values into coverageSnapshot,

src/internal/poll/writev.go

@@ -69,9 +69,7 @@ func (fd *FD) Writev(v *[][]byte) (int64, error) {
 		TestHookDidWritev(int(wrote))
 		n += int64(wrote)
 		consume(v, int64(wrote))
-		for i := range iovecs {
-			iovecs[i] = syscall.Iovec{}
-		}
+		clear(iovecs)
 		if err != nil {
 			if err == syscall.EINTR {
 				continue

src/runtime/debug/garbage.go

@@ -63,9 +63,7 @@ func ReadGCStats(stats *GCStats) {
 
 	if len(stats.PauseQuantiles) > 0 {
 		if n == 0 {
-			for i := range stats.PauseQuantiles {
-				stats.PauseQuantiles[i] = 0
-			}
+			clear(stats.PauseQuantiles)
 		} else {
 			// There's room for a second copy of the data in stats.Pause.
 			// See the allocation at the top of the function.

src/runtime/mbitmap_allocheaders.go

@@ -544,9 +544,7 @@ func bulkBarrierPreWriteSrcOnly(dst, src, size uintptr, typ *abi.Type) {
 func (s *mspan) initHeapBits(forceClear bool) {
 	if (!s.spanclass.noscan() && heapBitsInSpan(s.elemsize)) || s.isUserArenaChunk {
 		b := s.heapBits()
-		for i := range b {
-			b[i] = 0
-		}
+		clear(b)
 	}
 }
 

src/runtime/memmove_test.go

@@ -240,9 +240,7 @@ func TestMemmoveAtomicity(t *testing.T) {
 				for i := range src {
 					src[i] = &x
 				}
-				for i := range dst {
-					dst[i] = nil
-				}
+				clear(dst)
 
 				var ready atomic.Uint32
 				go func() {

src/runtime/netpoll_wasip1.go

@@ -205,9 +205,7 @@ func netpoll(delay int64) (gList, int32) {
 	}
 
 	evts = evts[:len(pollsubs)]
-	for i := range evts {
-		evts[i] = event{}
-	}
+	clear(evts)
 
 retry:
 	var nevents size

src/runtime/write_err_android.go

@@ -80,9 +80,7 @@ func writeErr(b []byte) {
 		if v == '\n' || writePos == len(dst)-1 {
 			dst[writePos] = 0
 			write(writeFD, unsafe.Pointer(&writeBuf[0]), int32(hlen+writePos))
-			for i := range dst {
-				dst[i] = 0
-			}
+			clear(dst)
 			writePos = 0
 		}
 	}