runtime: clean up adjustpointer and eliminate write barrier

Commit a5c3bbe0 modified adjustpointers to use *uintptrs instead of
*unsafe.Pointers for manipulating stack pointers for clarity and to
eliminate the unnecessary write barrier when writing the updated stack
pointer.

This commit makes the equivalent change to adjustpointer.

Change-Id: I6dc309590b298bdd86ecdc9737db848d6786c3f7
Reviewed-on: https://go-review.googlesource.com/17148Reviewed-by: Rick Hudson <rlh@golang.org>
Run-TryBot: Austin Clements <austin@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>

src/runtime/stack.go

@@ -521,15 +521,15 @@ type adjustinfo struct {
 // Adjustpointer checks whether *vpp is in the old stack described by adjinfo.
 // If so, it rewrites *vpp to point into the new stack.
 func adjustpointer(adjinfo *adjustinfo, vpp unsafe.Pointer) {
-	pp := (*unsafe.Pointer)(vpp)
+	pp := (*uintptr)(vpp)
 	p := *pp
 	if stackDebug >= 4 {
-		print("        ", pp, ":", p, "\n")
+		print("        ", pp, ":", hex(p), "\n")
 	}
-	if adjinfo.old.lo <= uintptr(p) && uintptr(p) < adjinfo.old.hi {
-		*pp = add(p, adjinfo.delta)
+	if adjinfo.old.lo <= p && p < adjinfo.old.hi {
+		*pp = p + adjinfo.delta
 		if stackDebug >= 3 {
-			print("        adjust ptr ", pp, ":", p, " -> ", *pp, "\n")
+			print("        adjust ptr ", pp, ":", hex(p), " -> ", hex(*pp), "\n")
 		}
 	}
 }