[PATCH] Teach IndVarSimplify to add nuw and nsw to operations that provably don't overflow.

[Sanjoy Das]

> Perhaps it would help to explain it slightly differently: There are
> optimizations which we can only perform by *removing* any no-wrap flags. But
> we don't know whether that optimization or the no-wrap flags is more
> important, and so we have to make a choice, and the choice is to preserve
> the flags at the expense of the transformation. Thus, adding flags can

Is this choice always in favor of retaining the flags?  Or is it a
per-transform decision?

> reduce the set of combines which actually occur even though they don't
> reduce the set of combines which are valid.

Thanks, I understand the situation now.

>
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