// loop because there might be backedges that haven't been visited yet.
			mem = memDefsAtBlockEnds[b.Preds[j].b.ID]
		}
		memDefsAtBlockEnds[b.ID] = mem
		if f.pass.debug > 2 {
			fmt.Printf("memDefsAtBlockEnds[%s] = %s\n", b, mem)
		}
	}

	// Maps from block to newly-inserted phi function in block.
	newmemphis := make(map[*Block]rewrite)