runtime: only clear pointer-containing memory during map delete

When deleting entries from a map, only clear the key and value
if they contain pointers. And use memclrHasPointers to do so.

While we're here, specialize key clearing in mapdelete_faststr,
and fix another missed usage of add in mapdelete.

Benchmarking impeded by #21546.

Change-Id: I3f6f924f738d6b899b722d6438e9e63f52359b84
Reviewed-on: https://go-review.googlesource.com/57630
Run-TryBot: Josh Bleecher Snyder <josharian@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Keith Randall <khr@golang.org>

src/runtime/hashmap.go

@@ -681,16 +681,20 @@ func mapdelete(t *maptype, h *hmap, key unsafe.Pointer) {
 			if !alg.equal(key, k2) {
 				continue
 			}
+			// Only clear key if there are pointers in it.
 			if t.indirectkey {
 				*(*unsafe.Pointer)(k) = nil
-			} else {
-				typedmemclr(t.key, k)
+			} else if t.key.kind&kindNoPointers == 0 {
+				memclrHasPointers(k, t.key.size)
 			}
-			v := unsafe.Pointer(uintptr(unsafe.Pointer(b)) + dataOffset + bucketCnt*uintptr(t.keysize) + i*uintptr(t.valuesize))
-			if t.indirectvalue {
-				*(*unsafe.Pointer)(v) = nil
-			} else {
-				typedmemclr(t.elem, v)
+			// Only clear value if there are pointers in it.
+			if t.indirectvalue || t.elem.kind&kindNoPointers == 0 {
+				v := add(unsafe.Pointer(b), dataOffset+bucketCnt*uintptr(t.keysize)+i*uintptr(t.valuesize))
+				if t.indirectvalue {
+					*(*unsafe.Pointer)(v) = nil
+				} else {
+					memclrHasPointers(v, t.elem.size)
+				}
 			}
 			b.tophash[i] = empty
 			h.count--

src/runtime/hashmap_fast.go

@@ -652,9 +652,15 @@ func mapdelete_fast32(t *maptype, h *hmap, key uint32) {
 			if key != *(*uint32)(k) || b.tophash[i] == empty {
 				continue
 			}
-			typedmemclr(t.key, unsafe.Pointer(k))
-			v := unsafe.Pointer(uintptr(unsafe.Pointer(b)) + dataOffset + bucketCnt*4 + i*uintptr(t.valuesize))
-			typedmemclr(t.elem, v)
+			// Only clear key if there are pointers in it.
+			if t.key.kind&kindNoPointers == 0 {
+				memclrHasPointers(k, t.key.size)
+			}
+			// Only clear value if there are pointers in it.
+			if t.elem.kind&kindNoPointers == 0 {
+				v := unsafe.Pointer(uintptr(unsafe.Pointer(b)) + dataOffset + bucketCnt*4 + i*uintptr(t.valuesize))
+				memclrHasPointers(v, t.elem.size)
+			}
 			b.tophash[i] = empty
 			h.count--
 			goto done
@@ -699,9 +705,15 @@ func mapdelete_fast64(t *maptype, h *hmap, key uint64) {
 			if key != *(*uint64)(k) || b.tophash[i] == empty {
 				continue
 			}
-			typedmemclr(t.key, unsafe.Pointer(k))
-			v := unsafe.Pointer(uintptr(unsafe.Pointer(b)) + dataOffset + bucketCnt*8 + i*uintptr(t.valuesize))
-			typedmemclr(t.elem, v)
+			// Only clear key if there are pointers in it.
+			if t.key.kind&kindNoPointers == 0 {
+				memclrHasPointers(k, t.key.size)
+			}
+			// Only clear value if there are pointers in it.
+			if t.elem.kind&kindNoPointers == 0 {
+				v := unsafe.Pointer(uintptr(unsafe.Pointer(b)) + dataOffset + bucketCnt*8 + i*uintptr(t.valuesize))
+				memclrHasPointers(v, t.elem.size)
+			}
 			b.tophash[i] = empty
 			h.count--
 			goto done
@@ -752,9 +764,12 @@ func mapdelete_faststr(t *maptype, h *hmap, ky string) {
 			if k.str != key.str && !memequal(k.str, key.str, uintptr(key.len)) {
 				continue
 			}
-			typedmemclr(t.key, unsafe.Pointer(k))
-			v := unsafe.Pointer(uintptr(unsafe.Pointer(b)) + dataOffset + bucketCnt*2*sys.PtrSize + i*uintptr(t.valuesize))
-			typedmemclr(t.elem, v)
+			*(*string)(kptr) = ""
+			// Only clear value if there are pointers in it.
+			if t.elem.kind&kindNoPointers == 0 {
+				v := unsafe.Pointer(uintptr(unsafe.Pointer(b)) + dataOffset + bucketCnt*2*sys.PtrSize + i*uintptr(t.valuesize))
+				memclrHasPointers(v, t.elem.size)
+			}
 			b.tophash[i] = empty
 			h.count--
 			goto done