[Bug tree-optimization/101240] [missed optimization] Transitivity of less-than and less-or-equal

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101240

Richard Biener <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Blocks|                            |85316
   Last reconfirmed|                            |2021-06-29
                 CC|                            |amacleod at redhat dot com
             Status|UNCONFIRMED                 |NEW
     Ever confirmed|0                           |1

--- Comment #1 from Richard Biener <rguenth at gcc dot gnu.org> ---
EVRP sees

  <bb 2> :
  _1 = (*a_8(D))[0];
  _2 = (*a_8(D))[1];
  if (_1 < _2)
    goto <bb 3>; [INV]
  else
    goto <bb 5>; [INV]

  <bb 3> :
  _4 = (*a_8(D))[2];
  if (_2 < _4)
    goto <bb 4>; [INV]
  else
    goto <bb 5>; [INV]

  <bb 4> :
  __builtin_unreachable ();

  <bb 5> :
  _6 = (*a_8(D))[2];
  _9 = _1 < _6;

so predicate analysis should handle this (but it does not).  Btw, I fixed
the testcase for you:

#define ALWAYS_TRUE(x) do { if (x) __builtin_unreachable(); } while (false)
bool test_array(unsigned (&a)[3]) {
  ALWAYS_TRUE(a[0] < a[1] && a[1] < a[2]);
  return a[0] < a[2];
}


Referenced Bugs:

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=85316
[Bug 85316] [meta-bug] VRP range propagation missed cases