{name: "AtomicStore8", argLength: 3, typ: "Mem", hasSideEffects: true},                     // Store arg1 to *arg0.  arg2=memory.  Returns memory.
	{name: "AtomicStore32", argLength: 3, typ: "Mem", hasSideEffects: true},                    // Store arg1 to *arg0.  arg2=memory.  Returns memory.
	{name: "AtomicStore64", argLength: 3, typ: "Mem", hasSideEffects: true},                    // Store arg1 to *arg0.  arg2=memory.  Returns memory.

		// SYNC
		{name: "LoweredAtomicStore8", argLength: 3, reg: gpstore, faultOnNilArg0: true, hasSideEffects: true},
		{name: "LoweredAtomicStore32", argLength: 3, reg: gpstore, faultOnNilArg0: true, hasSideEffects: true},
		{name: "LoweredAtomicStorezero", argLength: 2, reg: gpstore0, faultOnNilArg0: true, hasSideEffects: true},

		// atomic exchange.
		// store arg1 to arg0. arg2=mem. returns <old content of *arg0, memory>.

		{name: "LoweredAtomicStore8", argLength: 3, reg: gpstore, faultOnNilArg0: true, hasSideEffects: true},
		{name: "LoweredAtomicStore32", argLength: 3, reg: gpstore, faultOnNilArg0: true, hasSideEffects: true},
		{name: "LoweredAtomicStore64", argLength: 3, reg: gpstore, faultOnNilArg0: true, hasSideEffects: true},
		// store zero to arg0. arg1=mem. returns memory.

		{name: "LoweredAtomicStore8", argLength: 3, reg: gpstore, faultOnNilArg0: true, hasSideEffects: true},
		{name: "LoweredAtomicStore32", argLength: 3, reg: gpstore, faultOnNilArg0: true, hasSideEffects: true},
		{name: "LoweredAtomicStore64", argLength: 3, reg: gpstore, faultOnNilArg0: true, hasSideEffects: true},
		// store zero to arg0. arg1=mem. returns memory.

		{name: "LoweredAtomicStore8", argLength: 3, reg: gpstore, faultOnNilArg0: true, hasSideEffects: true},
		{name: "LoweredAtomicStore32", argLength: 3, reg: gpstore, faultOnNilArg0: true, hasSideEffects: true},
		{name: "LoweredAtomicStore64", argLength: 3, reg: gpstore, faultOnNilArg0: true, hasSideEffects: true},

		// Atomic exchange.
		// store arg1 to *arg0. arg2=mem. returns <old content of *arg0, memory>.

		{name: "LoweredAtomicAnd32", argLength: 3, reg: gpstore, asm: "AND", faultOnNilArg0: true, hasSideEffects: true},
		{name: "LoweredAtomicOr8", argLength: 3, reg: gpstore, asm: "OR", faultOnNilArg0: true, hasSideEffects: true},
		{name: "LoweredAtomicOr32", argLength: 3, reg: gpstore, asm: "OR", faultOnNilArg0: true, hasSideEffects: true},

					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,")
			}

	// 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