}

func (fwdRefAux) CanBeAnSSAAux() {}

// insertPhis finds all the places in the function where a phi is
// necessary and inserts them.
// Uses FwdRef ops to find all uses of variables, and s.defvars to find
// all definitions.
// Phi values are inserted, and all FwdRefs are changed to a Copy
// of the appropriate phi or definition.
// TODO: make this part of cmd/compile/internal/ssa somehow?
func (s *state) insertPhis() {

		for i := 0; i < len(b.Values); i++ {
			phi := b.Values[i]
			if phi.Uses == 0 || phi == ctl || phi.Op != OpPhi {
				continue
			}
			fixPhi(phi, i)
			if phi.Block == b {
				continue
			}
			// phi got moved to a different block with v.moveTo.
			// Adjust phi values in this new block that refer
			// to phi to refer to the corresponding phi arg instead.
			// phi used to be evaluated prior to this block,

	// Insert phi functions as necessary for future changes to flow graph.
	for i, emc := range tofixBackedges {
		e := emc.e
		h := e.b

		// find the phi function for the memory input at "h", if there is one.
		var headerMemPhi *Value // look for header mem phi

		for _, v := range h.Values {
			if v.Op == OpPhi && v.Type.IsMemory() {
				headerMemPhi = v
			}
		}

		if headerMemPhi == nil {

		b.Fatalf("inconsistent state for %v, num predecessors: %d, num phi args: %d", phi, n, numPhiArgs)
	}
	phi.Args[i].Uses--
	phi.Args[i] = phi.Args[n]
	phi.Args[n] = nil
	phi.Args = phi.Args[:n]
	phielimValue(phi)
}

// LackingPos indicates whether b is a block whose position should be inherited
// from its successors.  This is true if all the values within it have unreliable positions

	// Recursively decompose phis for each field.
	for _, f := range fields[:n] {
		decomposeUserPhi(f)
	}
}

// decomposeArrayPhi replaces phi-of-array with arraymake(phi-of-array-element),
// and then recursively decomposes the element phi.
func decomposeArrayPhi(v *Value) {
	t := v.Type
	if t.NumElem() == 0 {
		v.reset(OpArrayMake0)
		return
	}
	if t.NumElem() != 1 {

	for _, use := range t.defUse[val] {
		if val == use {
			// Phi may refer to itself as uses, ignore them to avoid re-visiting phi
			// for performance reason
			continue
		}
		t.uses = append(t.uses, use)
	}
	for _, block := range t.defBlock[val] {
		if t.visitedBlock[block.ID] {
			t.propagate(block)
		}
	}
}

// meet meets all of phi arguments and computes result lattice

	case "amd64":
		const maxcost = 2
		phi := 0
		other := 0
		for _, v := range post.Values {
			if v.Op == OpPhi {
				// Each phi results in CondSelect, which lowers into CMOV,
				// CMOV has latency >1 on most CPUs.
				phi++
			}
			for _, x := range v.Args {
				if x.Block == no || x.Block == yes {
					other++
				}
			}
		}
		cost := phi * 1
		if phi > 1 {

	if f.scheduled {
		for _, b := range f.Blocks {
			seenNonPhi := false
			for _, v := range b.Values {
				switch v.Op {
				case OpPhi:
					if seenNonPhi {
						f.Fatalf("phi after non-phi @ %s: %s", b, v)
					}
				default:
					seenNonPhi = true
				}
			}
		}
	}
}

// domCheck reports whether x dominates y (including x==y).

	// tuple selectors must be tightened to generators and de-duplicated before scheduling
	{"tighten tuple selectors", "schedule"},
	// remove critical edges before phi tighten, so that phi args get better placement
	{"critical", "phi tighten"},
	// don't layout blocks until critical edges have been removed
	{"critical", "layout"},
	// regalloc requires the removal of all critical edges
	{"critical", "regalloc"},

		Bloc("b2",
			Valu("ptr2", OpAddr, ptrType, 0, nil, "sb"),
			Goto("checkPtr")),
		// both ptr1 and ptr2 are guaranteed non-nil here
		Bloc("checkPtr",
			Valu("phi", OpPhi, ptrType, 0, nil, "ptr1", "ptr2"),
			Valu("bool2", OpIsNonNil, c.config.Types.Bool, 0, nil, "phi"),
			If("bool2", "extra", "exit")),
		Bloc("extra",
			Goto("exit")),
		Bloc("exit",
			Exit("mem")))

	CheckFunc(fun.f)
	nilcheckelim(fun.f)