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From: "jakub at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug tree-optimization/107591] New: range-op{,-float}.cc for x * x
Date: Wed, 09 Nov 2022 15:37:06 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D107591

            Bug ID: 107591
           Summary: range-op{,-float}.cc for x * x
           Product: gcc
           Version: 13.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: jakub at gcc dot gnu.org
  Target Milestone: ---

int
foo (int x)
{
  if (x < -13 || x > 26)
    return -1;
  return x * x;
}

results in
x_4(D) :      [irange] int [-13, 26]
_5  : [irange] int [-338, 676]
That is unnecessarily pessimized, because it only computes [-13, 26] * [-13,
26]
range without taking into account that both operands are the same.
For the powi (x, 2) case the range is actually [0, 26 * 26], i.e. we should=
n't
do a cross product for it, just compute the -13 * -13, 0 * 0 (if 0 is in the
range) and 26 * 26 products and form from that the range (I admit I haven't
thought about unsigned or wrapping stuff).

On the PR107569 testcase it is on frange:
  _3 =3D u_2(D)->x;
  _6 =3D _3 * _3;
  _7 =3D u_2(D)->y;
  _8 =3D _7 * _7;
  _9 =3D _6 + _8;
  if (_9 u>=3D 0.0)
If we don't know anything further about u_2(D)->x and u_2(D)->y, VARYING *
VARYING is [0, +Inf] +-NAN, added twice is the same (note, unless
-fno-signed-zeros, it should be really [+0, +Inf] +-NAN, not [-0, +Inf] +-N=
AN,
but it doesn't matter for the u>=3D 0.0 comparison).
And then we can fold u>=3D 0.0 to true.=