nextMem := f.Cache.allocValueSlice(f.NumValues())
	defer f.Cache.freeValueSlice(nextMem)

	// inBlockUses records whether a value is used in the block
	// in which it lives. (block control values don't count as uses.)
	inBlockUses := f.Cache.allocBoolSlice(f.NumValues())
	defer f.Cache.freeBoolSlice(inBlockUses)
	if f.Config.optimize {
		for _, b := range f.Blocks {
			for _, v := range b.Values {