//
// Phi values are special, as always. We define two kinds of phis, those
// where the merge happens in a register (a "register" phi) and those where
// the merge happens in a stack location (a "stack" phi).
//
// A register phi must have the phi and all of its inputs allocated to the
// same register. Register phis are spilled similarly to regular ops.
//

		// That means this code:
		//
		//	loop:
		//		ind = (Phi (Const [x]) nxt),
		//		if ind < end
		//		then goto enter_loop
		//		else goto exit_loop
		//
		//	enter_loop:
		//		do something without using ind nor nxt
		//		nxt = inc + ind
		//		goto loop
		//
		//	exit_loop:
		//
		// is rewritten to:
		//
		//	loop:
		//		ind = (Phi end nxt)
		//		if (Const [x]) < ind

			// Since target and load are in the same block
			// we can stop searching when we leave the block.
			continue
		}
		if v.Op == OpPhi {
			// A Phi implies we have reached the top of the block.
			// The memory phi, if it exists, is always
			// the first logical store in the block.
			continue
		}
		if v.Type.IsTuple() && v.Type.FieldType(1).IsMemory() {

				return !opcodeTable[v.Op].zeroWidth
			} else {
				return v.Op == OpInitMem
			}
		}

		// Examine the prolog portion of the block to process special
		// zero-width ops such as Arg, Phi, LoweredGetClosurePtr (etc)
		// whose lifetimes begin at the block starting point. In an
		// entry block, allow for the possibility that we may see Arg
		// ops that appear _after_ other non-zero-width operations.