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From: "pinskia at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug tree-optimization/101024] New: Missed min expression at phiopt1
Date: Fri, 11 Jun 2021 04:00:23 +0000
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X-Bugzilla-Component: tree-optimization
X-Bugzilla-Version: 12.0
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D101024

            Bug ID: 101024
           Summary: Missed min expression at phiopt1
           Product: gcc
           Version: 12.0
            Status: UNCONFIRMED
          Keywords: missed-optimization
          Severity: enhancement
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: pinskia at gcc dot gnu.org
  Target Milestone: ---

Take:
unsigned f(int nunits)
{
  int units_per =3D 32 / (8);


  unsigned int chunk_nunits =3D ((nunits) < (units_per) ? (nunits) :
(units_per));
  return chunk_nunits;
}
-------- CUT ------
Compile with the C++ front-end and -O2 (note C++ is needed as fold won't
convert ?: into min/max expression due to lvalue requirements).
You will notice this is not caught by phiopt1 even though it should be whil=
e it
is caught now (on the trunk) by phiopt2 (match-and-simplify).  That is the
minmax_replacement does not handle the above case but match does.

Note this shows up in read code (GCC) in assemble_real (varasm.c). There are
two cases of this in assemble_real but only one of the two is caught in phi=
opt2
though because there looks like some jump threading that had happened before
that causes other issues.

I am filing this as a bug only so I can keep track of moving minmax_replace=
ment
to match-and-simplify.=