Re: [PATCH] Remove unnecessary "& 1" in year_month_day_last::day()

[Cassio Neri <cassio.neri@gmail.com>]

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I could not find any entry in gcc's bugzilla for that. Perhaps my search
wasn't good enough.


On Sun, 5 Nov 2023 at 15:58, Marc Glisse <marc.glisse@inria.fr> wrote:

> On Sun, 5 Nov 2023, Cassio Neri wrote:
>
> > When year_month_day_last::day() was implemented, Dr. Matthias Kretz
> realised
> > that the operation "& 1" wasn't necessary but we did not patch it at that
> > time. This patch removes the unnecessary operation.
>
> Is there an entry in gcc's bugzilla about having the optimizer handle this
> kind of optimization?
>
> unsigned f(unsigned x){
>    if(x>=32)__builtin_unreachable();
>    return 30|(x&1); // --> 30|x
> }
>
> (that optimization would come in addition to your patch, doing the
> optimization by hand is still a good idea)
>
> It looks like the criterion would be a|(b&c) when the possible 1 bits of b
> are included in the certainly 1 bits of a|c.
>
> --
> Marc Glisse
>