Stacking weapon rerolls

[herrhauptmann]

Several feats and abilities allow you to reroll your damage dice.

Great Weapon Fighting Style: Reroll on a 1 or 2. Must use new roll.
Piercer: 1/turn, reroll just one damage dice. Must use new roll.
Savage Attacker: Use either roll.

Since two of these say you have to use the new roll, is it even possible to stack these abilities? Obviously GWF or Piercer alone are intended to stop you from rerolling constantly, but what if you have both?

[Chronos]

I'd say that they stack. Ordinarily when you don't have any of these abilities, you have to use whatever the result of your roll is, and these abilities change that. So I'd say they also work on the condition of "must use the results of the reroll".

[Samayu]

One could interpret the rules to indicate that no, you can't reroll that die. If you're going to reroll something, it must be a different die. But one could also say that the separate reroll clauses override each other. I think that interpretation is the most correct. If you spend resources on those features, why shouldn't you be able to cash in on them? And this certainly isn't game breaking.

Edit:
Also, multiple rerolls on the same die have diminishing returns anyway, so yeah, give them all the rerolls.

[PhoenixPhyre]

I won't speak to what the rules are.

However, I will say that rerolls (especially conditional rerolls) are fun...and extremely expensive in the only currency that matters. Game time. Having to decide "do I reroll" and then rerolling, especially if it's only part of the result or you don't know until afterwards breaks the action-resolution flow worse than almost anything else (interrupts, especially conditional ones, are a little worse).

As a result, I'm in favor of a houserule that no more than one reroll ability can be used on any given action resolution. If you rerolled the attack, you can't reroll damage. If you silvery barbs once, no one else can do it again on that action.