{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.

		{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},

		// 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.