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From: "roger at nextmovesoftware dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug target/43892] PowerPC suboptimal "add with carry" optimization
Date: Tue, 29 Aug 2023 17:43:33 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D43892

--- Comment #39 from Roger Sayle <roger at nextmovesoftware dot com> ---
My apologies for dropping the ball on this patch (series)... My only access=
 to
PowerPC hardware is/was via the GCC compile farm, which complicates things.

Shortly after David's approval, Segher enquired whether the patch could be
modified to also handle -mcpu=3Dpower10 (which represents carry differently=
):
https://gcc.gnu.org/pipermail/gcc-patches/2021-December/586868.html

Trying to (also) address this then openned up a rabbit hole/can of worms
related to how middle-end (and rs6000.md) represents overflow, which includ=
ed a
combine patch:
https://gcc.gnu.org/pipermail/gcc-patches/2021-December/586572.html

Soon after GCC entered stage 4 (or stage 3), and the above patches (and an
unsubmitted one for power10) simply got lost in the backlog.  I believe this
patch is sound, but unfortunately I don't have the bandwidth/patience to
(re)check it against mainline on (multiple variants of) rs6000.

If one of the IBM folks could take it from here, that'd be much appreciated=
.=