[Bug tree-optimization/56352] New: Simplify testing of related conditions in for loop

[Bug tree-optimization/56352] New: Simplify testing of related conditions in for loop

[josh.m.conner at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56352

             Bug #: 56352
           Summary: Simplify testing of related conditions in for loop
    Classification: Unclassified
           Product: gcc
           Version: 4.8.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: josh.m.conner@gmail.com


If we have a loop like this:

for (i = 0; i < a && i < b; i++)
{
  /* Code which cannot affect i, a, or b */
}

gcc should be able to optimize this into:

tmp = MIN(a,b)
for (i = 0; i < tmp; i++)
{
  /* Body */
}

But it does not.  Similarly, code like:

for (i = 0; i < a; i++)
{
  if (i >= b)
    break;

  /* Code which cannot affect i, a, or b */
}

Should be similarly optimized.

[Bug tree-optimization/56352] Simplify testing of related conditions in for loop

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=56352

--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Testcase:

int f(int);
void g(int a, int b)
{
    int i;
for (i = 0; i < a; i++)
{
  if (i >= b)
    break;

  f(i);
}

}

[Bug tree-optimization/56352] Simplify testing of related conditions in for loop

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=56352

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |missed-optimization
             Status|UNCONFIRMED                 |RESOLVED
      Known to fail|                            |8.1.0, 8.5.0
         Resolution|---                         |DUPLICATE
      Known to work|                            |10.1.0, 9.1.0, 9.4.0

--- Comment #2 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
GCC9+ does the correct thing:
.L5:
        movl    %ebx, %edi
        addl    $1, %ebx
        call    f(int)
        cmpl    %ebx, %ebp
        jg      .L5

GCC 8.5 had:
  _9 = b_5(D) <= i_7;
  _8 = a_4(D) <= i_7;
  _10 = _8 | _9;

This was fixed by r9-104.
Note there is some issues with mixing constants and non-constants but that is
still recorded in PR 85143.
And really this is a dup of bug 85143.

*** This bug has been marked as a duplicate of bug 85143 ***