replacing the VRP threader

[Aldy Hernandez]

On Tue, Sep 21, 2021 at 12:48 PM Aldy Hernandez <aldyh@redhat.com> wrote:

> SUMMARY
> =======
>
> The hybrid threader gets 14.5% more jump threads than the legacy code,
> but most of these threads are at the expense of other threading passes.
> The more it gets, the less DOM and the backward threader get.  That
> being said, there is a total improvement of 0.87% jump threads in the
> total compilation.

Well, it turns out we're considerably better than reported.

Andrew just found a one-line change in the path solver that improves
our VRP threading goodness to 18.5% and our overall jump threading
gains to 1.28%.

Yay!
Aldy