runtime: remove checkgc code from hashmap

Currently hashmap is riddled with code that attempts to force a GC on
the next allocation if checkgc is set. This no longer works as
originally intended with the concurrent collector, and is apparently
no longer used anyway.

Remove checkgc.

Change-Id: Ia6c17c405fa8821dc2e6af28d506c1133ab1ca0c
Reviewed-on: https://go-review.googlesource.com/8355
Reviewed-by: Keith Randall <khr@golang.org>

src/runtime/hashmap.go

@@ -96,9 +96,6 @@ const (
 
 	// sentinel bucket ID for iterator checks
 	noCheck = 1<<(8*ptrSize) - 1
-
-	// trigger a garbage collection at every alloc called from this code
-	checkgc = false
 )
 
 // A header for a Go map.
@@ -246,16 +243,10 @@ func makemap(t *maptype, hint int64, h *hmap, bucket unsafe.Pointer) *hmap {
 	// If hint is large zeroing this memory could take a while.
 	buckets := bucket
 	if B != 0 {
-		if checkgc {
-			memstats.next_gc = memstats.heap_alloc
-		}
 		buckets = newarray(t.bucket, uintptr(1)<<B)
 	}
 
 	// initialize Hmap
-	if checkgc {
-		memstats.next_gc = memstats.heap_alloc
-	}
 	if h == nil {
 		h = (*hmap)(newobject(t.hmap))
 	}
@@ -430,9 +421,6 @@ func mapassign1(t *maptype, h *hmap, key unsafe.Pointer, val unsafe.Pointer) {
 	hash := alg.hash(key, uintptr(h.hash0))
 
 	if h.buckets == nil {
-		if checkgc {
-			memstats.next_gc = memstats.heap_alloc
-		}
 		h.buckets = newarray(t.bucket, 1)
 	}
 
@@ -493,9 +481,6 @@ again:
 
 	if inserti == nil {
 		// all current buckets are full, allocate a new one.
-		if checkgc {
-			memstats.next_gc = memstats.heap_alloc
-		}
 		newb := (*bmap)(newobject(t.bucket))
 		h.setoverflow(t, b, newb)
 		inserti = &newb.tophash[0]
@@ -505,17 +490,11 @@ again:
 
 	// store new key/value at insert position
 	if t.indirectkey {
-		if checkgc {
-			memstats.next_gc = memstats.heap_alloc
-		}
 		kmem := newobject(t.key)
 		*(*unsafe.Pointer)(insertk) = kmem
 		insertk = kmem
 	}
 	if t.indirectvalue {
-		if checkgc {
-			memstats.next_gc = memstats.heap_alloc
-		}
 		vmem := newobject(t.elem)
 		*(*unsafe.Pointer)(insertv) = vmem
 		insertv = vmem
@@ -776,9 +755,6 @@ func hashGrow(t *maptype, h *hmap) {
 		throw("evacuation not done in time")
 	}
 	oldbuckets := h.buckets
-	if checkgc {
-		memstats.next_gc = memstats.heap_alloc
-	}
 	newbuckets := newarray(t.bucket, uintptr(1)<<(h.B+1))
 	flags := h.flags &^ (iterator | oldIterator)
 	if h.flags&iterator != 0 {
@@ -879,9 +855,6 @@ func evacuate(t *maptype, h *hmap, oldbucket uintptr) {
 				if (hash & newbit) == 0 {
 					b.tophash[i] = evacuatedX
 					if xi == bucketCnt {
-						if checkgc {
-							memstats.next_gc = memstats.heap_alloc
-						}
 						newx := (*bmap)(newobject(t.bucket))
 						h.setoverflow(t, x, newx)
 						x = newx
@@ -906,9 +879,6 @@ func evacuate(t *maptype, h *hmap, oldbucket uintptr) {
 				} else {
 					b.tophash[i] = evacuatedY
 					if yi == bucketCnt {
-						if checkgc {
-							memstats.next_gc = memstats.heap_alloc
-						}
 						newy := (*bmap)(newobject(t.bucket))
 						h.setoverflow(t, y, newy)
 						y = newy