cmd/compile: remove overflow pointer padding for nacl

CL 200077 removed nacl bits in the toolchain, but it misses the code to
add pointer overflow padding, which is specific for nacl.

This CL removes that part.

Passes toolstash-check.

Updates #30439

Change-Id: I1e77cade9f31690e16cd13d3445a98b500671252
Reviewed-on: https://go-review.googlesource.com/c/go/+/202159
Run-TryBot: Cuong Manh Le <cuong.manhle.vn@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Keith Randall <khr@golang.org>

src/cmd/compile/internal/gc/reflect.go

@@ -112,27 +112,6 @@ func bmap(t *types.Type) *types.Type {
 	elems := makefield("elems", arr)
 	field = append(field, elems)
 
-	// Make sure the overflow pointer is the last memory in the struct,
-	// because the runtime assumes it can use size-ptrSize as the
-	// offset of the overflow pointer. We double-check that property
-	// below once the offsets and size are computed.
-	//
-	// BUCKETSIZE is 8, so the struct is aligned to 64 bits to this point.
-	// On 32-bit systems, the max alignment is 32-bit, and the
-	// overflow pointer will add another 32-bit field, and the struct
-	// will end with no padding.
-	// On 64-bit systems, the max alignment is 64-bit, and the
-	// overflow pointer will add another 64-bit field, and the struct
-	// will end with no padding.
-	// On nacl/amd64p32, however, the max alignment is 64-bit,
-	// but the overflow pointer will add only a 32-bit field,
-	// so if the struct needs 64-bit padding (because a key or elem does)
-	// then it would end with an extra 32-bit padding field.
-	// Preempt that by emitting the padding here.
-	if int(elemtype.Align) > Widthptr || int(keytype.Align) > Widthptr {
-		field = append(field, makefield("pad", types.Types[TUINTPTR]))
-	}
-
 	// If keys and elems have no pointers, the map implementation
 	// can keep a list of overflow pointers on the side so that
 	// buckets can be marked as having no pointers.
@@ -196,7 +175,7 @@ func bmap(t *types.Type) *types.Type {
 	}
 
 	// Double-check that overflow field is final memory in struct,
-	// with no padding at end. See comment above.
+	// with no padding at end.
 	if overflow.Offset != bucket.Width-int64(Widthptr) {
 		Fatalf("bad offset of overflow in bmap for %v", t)
 	}