From: Joseph Myers <joseph@codesourcery.com>
To: Aldy Hernandez <aldyh@redhat.com>
Cc: GCC patches <gcc-patches@gcc.gnu.org>, Jakub Jelinek <jakub@redhat.com>
Subject: Re: [COMMITTED] Implement ranger folder for __builtin_signbit.
Date: Thu, 1 Sep 2022 16:41:10 +0000 [thread overview]
Message-ID: <alpine.DEB.2.22.394.2209011632000.550568@digraph.polyomino.org.uk> (raw)
In-Reply-To: <20220901111851.2595874-2-aldyh@redhat.com>
On Thu, 1 Sep 2022, Aldy Hernandez via Gcc-patches wrote:
> Now that we keep track of the signbit, we can use it to fold __builtin_signbit.
>
> I am assuming I don't have try too hard to get the actual signbit
> number and 1 will do. Especially, since we're inconsistent in trunk whether
> we fold the builtin or whether we calculate it at runtime.
The main thing to watch out for is cases where, in the abstract machine,
there is a single call executed to __builtin_signbit, but after code
transformations, some uses of the result of that call are optimized to use
a 0 or 1 value and other uses end up using a runtime value - inconsistency
between different calls is fine, inconsistency where only a single call is
executed in the abstract machine isn't. (Cf. bugs 102930, 85957, 93681,
93806, 93682, for example; the test in bug 93806 comment 27 is the sort of
thing to try.)
--
Joseph S. Myers
joseph@codesourcery.com
next prev parent reply other threads:[~2022-09-01 16:41 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-09-01 11:18 [COMMITTED] Add signbit property to frange to better model signed zeros Aldy Hernandez
2022-09-01 11:18 ` [COMMITTED] Implement ranger folder for __builtin_signbit Aldy Hernandez
2022-09-01 16:41 ` Joseph Myers [this message]
2022-09-01 18:25 ` Aldy Hernandez
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