[Bug tree-optimization/81184] [8 regression] gcc.dg/pr21643.c and gcc.dg/tree-ssa/phi-opt-11.c fail starting with r249450

["marxin at gcc dot gnu.org" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=81184

Martin Liška <marxin at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2017-06-23
                 CC|                            |jakub at gcc dot gnu.org
           Assignee|unassigned at gcc dot gnu.org      |marxin at gcc dot gnu.org
     Ever confirmed|0                           |1

--- Comment #1 from Martin Liška <marxin at gcc dot gnu.org> ---
Confirmed, I'm adding Jakub as author of original test-case.

The affected function changed from:

Optimizing range tests c_2(D) -[0, 31] and -[32, 32]
 into c_2(D) > 32
Removing basic block 3
;; basic block 3, loop depth 0
;;  pred:      
;;  succ:       4


fix_loop_structure: fixing up loops for function
f6 (unsigned char c)
{
  int _1;
  _Bool _5;

  <bb 2> [100.00%] [count: INV]:
  if (c_2(D) == 34)
    goto <bb 5>; [18.79%] [count: INV]
  else
    goto <bb 3>; [81.21%] [count: INV]

  <bb 3> [65.95%] [count: INV]:
  _5 = c_2(D) <= 32;
  if (_5 != 0)
    goto <bb 5>; [31.00%] [count: INV]
  else
    goto <bb 4>; [69.00%] [count: INV]

  <bb 4> [45.51%] [count: INV]:

  <bb 5> [100.00%] [count: INV]:
  # _1 = PHI <2(2), 0(4), 2(3)>
  return _1;

}

to:

Optimizing range tests c_2(D) -[32, 32] and -[34, 34]
 into (c_2(D) & 253) != 32
Width = 1 was chosen for reassociation
Merging blocks 2 and 3
fix_loop_structure: fixing up loops for function
f6 (unsigned char c)
{
  int _1;
  _Bool _4;
  unsigned char _5;

  <bb 2> [100.00%] [count: INV]:
  _5 = c_2(D) & 253;
  _4 = _5 == 32;
  if (_4 != 0)
    goto <bb 5>; [10.65%] [count: INV]
  else
    goto <bb 3>; [89.35%] [count: INV]

  <bb 3> [79.83%] [count: INV]:
  if (c_2(D) <= 31)
    goto <bb 4>; [18.79%] [count: INV]
  else
    goto <bb 5>; [81.21%] [count: INV]

  <bb 4> [15.00%] [count: INV]:

  <bb 5> [100.00%] [count: INV]:
  # _1 = PHI <0(3), 2(2), 2(4)>
  return _1;

}

On x86_64 it's different because the function looks as follows:

f6 (unsigned char c)
{
  int _1;
  _Bool _4;
  _Bool _5;
  _Bool _7;
  _Bool _8;
  _Bool _9;

  <bb 2> [100.00%] [count: INV]:
  _5 = c_2(D) == 32;
  _4 = c_2(D) == 34;
  _9 = c_2(D) <= 32;
  _7 = c_2(D) <= 31;
  _8 = _9 | _4;
  if (_8 != 0)
    goto <bb 3>; [15.00%] [count: INV]
  else
    goto <bb 4>; [85.00%] [count: INV]

  <bb 3> [15.00%] [count: INV]:

  <bb 4> [100.00%] [count: INV]:
  # _1 = PHI <0(2), 2(3)>
  return _1;

}

Note that the PR exposes problem where we are able to do predictions for
conditions, but
here we transform:

  if (c_2(D) == 34)
    goto <bb 3>; [10.65%] [count: INV]
  else
    goto <bb 4>; [89.35%] [count: INV]

into:
  _4 = c_2(D) == 34;

and then we do

  _8 = _9 | _4;
  if (_8 != 0)

It's related to PR79489.