Optimize/eliminate bounds checking

TODO: do better at it by tracking min/max values of integers. The
following straightforward code doesn't have its bounds checks removed:

    for _, n := range slice {
        println(n)
    }

src/runtime/hashmap.go

@@ -66,6 +66,7 @@ func hashmapMake(keySize, valueSize uint8) *hashmap {
 }
 
 // Set a specified key to a given value. Grow the map if necessary.
+//go:nobounds
 func hashmapSet(m *hashmap, key unsafe.Pointer, value unsafe.Pointer, hash uint32, keyEqual func(x, y unsafe.Pointer, n uintptr) bool) {
 	numBuckets := uintptr(1) << m.bucketBits
 	bucketNumber := (uintptr(hash) & (numBuckets - 1))
@@ -114,6 +115,7 @@ func hashmapSet(m *hashmap, key unsafe.Pointer, value unsafe.Pointer, hash uint3
 }
 
 // Get the value of a specified key, or zero the value if not found.
+//go:nobounds
 func hashmapGet(m *hashmap, key unsafe.Pointer, value unsafe.Pointer, hash uint32, keyEqual func(x, y unsafe.Pointer, n uintptr) bool) {
 	numBuckets := uintptr(1) << m.bucketBits
 	bucketNumber := (uintptr(hash) & (numBuckets - 1))