runtime: don't cache t.key.alg in evacuate

The number of times that alg has to be spilled
and restored makes it better to just reload it.

Change-Id: I2674752a889ecad59dab54da1d68fad03db1ca85
Reviewed-on: https://go-review.googlesource.com/56931
Run-TryBot: Josh Bleecher Snyder <josharian@gmail.com>
Reviewed-by: Daniel Martí <mvdan@mvdan.cc>
Reviewed-by: Keith Randall <khr@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

src/runtime/hashmap.go

@@ -1024,7 +1024,6 @@ func bucketEvacuated(t *maptype, h *hmap, bucket uintptr) bool {
 func evacuate(t *maptype, h *hmap, oldbucket uintptr) {
 	b := (*bmap)(add(h.oldbuckets, oldbucket*uintptr(t.bucketsize)))
 	newbit := h.noldbuckets()
-	alg := t.key.alg
 	if !evacuated(b) {
 		// TODO: reuse overflow buckets instead of using new ones, if there
 		// is no iterator using the old buckets.  (If !oldIterator.)
@@ -1073,8 +1072,8 @@ func evacuate(t *maptype, h *hmap, oldbucket uintptr) {
 				if !h.sameSizeGrow() {
 					// Compute hash to make our evacuation decision (whether we need
 					// to send this key/value to bucket x or bucket y).
-					hash := alg.hash(k2, uintptr(h.hash0))
-					if h.flags&iterator != 0 && !t.reflexivekey && !alg.equal(k2, k2) {
+					hash := t.key.alg.hash(k2, uintptr(h.hash0))
+					if h.flags&iterator != 0 && !t.reflexivekey && !t.key.alg.equal(k2, k2) {
 						// If key != key (NaNs), then the hash could be (and probably
 						// will be) entirely different from the old hash. Moreover,
 						// it isn't reproducible. Reproducibility is required in the