[Bug tree-optimization/65053] New: [5 Regression] PostgreSQL miscompilation

[Bug tree-optimization/65053] New: [5 Regression] PostgreSQL miscompilation

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65053

            Bug ID: 65053
           Summary: [5 Regression] PostgreSQL miscompilation
           Product: gcc
           Version: 5.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: jakub at gcc dot gnu.org

Following testcase is miscompiled at -O2 starting with r220164:

int i;

__attribute__ ((noinline))
unsigned int foo (void)
{
  return 0;
}

int
main ()
{
  unsigned int u = -1;
  if (u == -1)
    {
      unsigned int n = foo ();
      if (n > 0)
    u = n - 1;
    }

  while (u != -1)
    {
      asm ("" : "+g" (u));
      u = -1;
      i = 1;
    }

  if (i)
    __builtin_abort ();
  return 0;
}

[Bug tree-optimization/65053] [5 Regression] PostgreSQL miscompilation

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65053

Jakub Jelinek <jakub at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2015-02-13
   Target Milestone|---                         |5.0
     Ever confirmed|0                           |1

[Bug tree-optimization/65053] [5 Regression] PostgreSQL miscompilation

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65053

--- Comment #1 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
I believe this is a phiopt1 bug.
In *.ifcombine we have:
  <bb 2>:
  n_5 = foo ();
  if (n_5 != 0)
    goto <bb 3>;
  else
    goto <bb 4>;

  <bb 3>:
  # RANGE [0, 4294967294]
  u_6 = n_5 + 4294967295;

  <bb 4>:
  # u_3 = PHI <u_6(3), 4294967295(2)>
  goto <bb 6>;
which looks right, for non-zero n_5 u_6 really is != 0xffffffffU.
But then *.phiopt optimizes this into:
  <bb 2>:
  n_5 = foo ();
  # RANGE [0, 4294967294]
  u_6 = n_5 + 4294967295;
  goto <bb 4>;
which is wrong, either it should have adjusted the value range or drop it when
making u_6 unconditional.
What r220164 did is just start using the VR information during the next VRP
pass, but as the info is bogus due to phiopt, it resulted in wrong optimization
later on.

[Bug tree-optimization/65053] [5 Regression] PostgreSQL miscompilation

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65053

Jakub Jelinek <jakub at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |ASSIGNED
           Assignee|unassigned at gcc dot gnu.org      |jakub at gcc dot gnu.org

--- Comment #2 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
Created attachment 34749
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=34749&action=edit
gcc5-pr65053.patch

Untested fix.

[Bug tree-optimization/65053] [5 Regression] PostgreSQL miscompilation

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65053

Jakub Jelinek <jakub at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Priority|P3                          |P1

[Bug tree-optimization/65053] [5 Regression] PostgreSQL miscompilation

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65053

--- Comment #3 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
Author: jakub
Date: Fri Feb 13 23:20:31 2015
New Revision: 220700

URL: https://gcc.gnu.org/viewcvs?rev=220700&root=gcc&view=rev
Log:
    PR tree-optimization/65053
    * tree-ssa-phiopt.c (value_replacement): When moving assign before
    cond, either reset VR on lhs or set it to phi result VR.

    * gcc.c-torture/execute/pr65053-1.c: New test.
    * gcc.c-torture/execute/pr65053-2.c: New test.

Added:
    trunk/gcc/testsuite/gcc.c-torture/execute/pr65053-1.c
    trunk/gcc/testsuite/gcc.c-torture/execute/pr65053-2.c
Modified:
    trunk/gcc/ChangeLog
    trunk/gcc/testsuite/ChangeLog
    trunk/gcc/tree-ssa-phiopt.c

[Bug tree-optimization/65053] [5 Regression] PostgreSQL miscompilation

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65053

Jakub Jelinek <jakub at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|ASSIGNED                    |RESOLVED
         Resolution|---                         |FIXED

--- Comment #4 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
Fixed.