log.Fatalf("faultOnNilArg1 with aux %s not allowed", v.aux)
				}
			}
			if v.hasSideEffects {
				fmt.Fprintln(w, "hasSideEffects: true,")
			}
			if v.zeroWidth {
				fmt.Fprintln(w, "zeroWidth: true,")
			}
			if v.unsafePoint {
				fmt.Fprintln(w, "unsafePoint: true,")
			}

		{name: "XCHGL", argLength: 3, reg: gpstorexchg, asm: "XCHGL", aux: "SymOff", resultInArg0: true, faultOnNilArg1: true, hasSideEffects: true, symEffect: "RdWr"},
		{name: "XCHGQ", argLength: 3, reg: gpstorexchg, asm: "XCHGQ", aux: "SymOff", resultInArg0: true, faultOnNilArg1: true, hasSideEffects: true, symEffect: "RdWr"},

		// Atomic adds.

	exprs := op.split(e, seen)

	// Partition the slice of expressions into commutative sets.
	i := 0
	var sets [][]ast.Expr
	for j := 0; j <= len(exprs); j++ {
		if j == len(exprs) || analysisutil.HasSideEffects(info, exprs[j]) {
			if i < j {
				sets = append(sets, exprs[i:j])
			}
			i = j + 1
		}
	}

	return sets
}

// checkRedundant checks for expressions of the form
//
//	e && e

		hasSideEffects: true,
		generic:        true,
	},
	{
		name:           "AtomicExchange64",
		argLen:         3,
		hasSideEffects: true,
		generic:        true,
	},
	{
		name:           "AtomicAdd32",
		argLen:         3,
		hasSideEffects: true,
		generic:        true,
	},
	{
		name:           "AtomicAdd64",
		argLen:         3,
		hasSideEffects: true,

	return true
}

// isEmpty reports whether b contains any live values.
// There may be false positives.
func isEmpty(b *Block) bool {
	for _, v := range b.Values {
		if v.Uses > 0 || v.Op.IsCall() || v.Op.HasSideEffects() || v.Type.IsVoid() || opcodeTable[v.Op].nilCheck {
			return false
		}
	}
	return true
}

// fuseBlockPlain handles a run of blocks with length >= 2,

				q = append(q, v)
				if v.Pos.IsStmt() != src.PosNotStmt {
					liveOrderStmts = append(liveOrderStmts, v)
				}
			}
		}
		for _, v := range b.Values {
			if (opcodeTable[v.Op].call || opcodeTable[v.Op].hasSideEffects || opcodeTable[v.Op].nilCheck) && !live[v.ID] {
				live[v.ID] = true
				q = append(q, v)
				if v.Pos.IsStmt() != src.PosNotStmt {
					liveOrderStmts = append(liveOrderStmts, v)
				}
			}

	// or anything else with side-effects
	for _, v := range b.Values {
		if v.Op == OpPhi || isDivMod(v.Op) || isPtrArithmetic(v.Op) || v.Type.IsMemory() ||
			v.MemoryArg() != nil || opcodeTable[v.Op].hasSideEffects {
			return false
		}
	}
	return true
}

func isDivMod(op Op) bool {
	switch op {
	case OpDiv8, OpDiv8u, OpDiv16, OpDiv16u,
		OpDiv32, OpDiv32u, OpDiv64, OpDiv64u, OpDiv128u,

		// Ignore Args since they can't be autos.
		if v.Op.SymEffect() != SymNone && v.Op != OpArg {
			panic("unhandled op with sym effect")
		}

		if v.Uses == 0 && v.Op != OpNilCheck && !v.Op.IsCall() && !v.Op.HasSideEffects() || len(args) == 0 {
			// We need to keep nil checks even if they have no use.
			// Also keep calls and values that have side effects.
			return
		}

	if v.Type.IsMemory() {
		// We don't need to preserve all memory ops, but we do need
		// to keep calls at least (because they might have
		// synchronization operations we can't see).
		return false
	}
	if v.Op.HasSideEffects() {
		// These are mostly synchronization operations.
		return false
	}
	return true
}

// AutoVar returns a *Name and int64 representing the auto variable and offset within it

	faultOnNilArg1    bool      // this op will fault if arg1 is nil (and aux encodes a small offset)
	usesScratch       bool      // this op requires scratch memory space
	hasSideEffects    bool      // for "reasons", not to be eliminated.  E.g., atomic store, #19182.
	zeroWidth         bool      // op never translates into any machine code. example: copy, which may sometimes translate to machine code, is not zero-width.