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From: "amacleod at redhat dot com" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug tree-optimization/102650] [12 Regression] Dead Code Elimination
 Regression at -O3 (trunk vs 11.2.0)
Date: Wed, 19 Jan 2022 15:15:47 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D102650

--- Comment #6 from Andrew Macleod <amacleod at redhat dot com> ---
(In reply to Richard Biener from comment #4)
> If it is undefined it should be unreachable, not switch to a random static
> branch ;)  (defeating uninit diagnostics, of course)

Well, its not unreachable.. we reach that code always and have to take one =
of
the branches. It just uses an automatic variable which hasn't been initiali=
zed,
making it undefined.

We could choose whatever value we want for it.  If we chose non-zero, the c=
all
would be eliminated.  It would take analysis of some sort to decide which
branch is more profitable to remove in the presence of undefined...=20=20

THis seems like something that maybe uninit could do :-)  Hey, this is
uninitialized, tell the user and then see what the most profitable value to
assume for it going forward would be and set it to that value :-)=