[Bug tree-optimization/95729] New: Failure to optimize away certain returns when the condition to reach them is a calculation that already results in that value

[Bug tree-optimization/95729] New: Failure to optimize away certain returns when the condition to reach them is a calculation that already results in that value

[gabravier at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95729

            Bug ID: 95729
           Summary: Failure to optimize away certain returns when the
                    condition to reach them is a calculation that already
                    results in that value
           Product: gcc
           Version: 11.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: gabravier at gmail dot com
  Target Milestone: ---

int f(int a, int b)
{
    if (a != b)
        return a - b;
    else
        return 0;
}

This can be optimized to `return a - b;`. This optimization is done by LLVM,
but not by GCC.

[Bug tree-optimization/95729] Failure to optimize away certain returns when the condition to reach them is a calculation that already results in that value

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95729

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Severity|normal                      |enhancement

[Bug tree-optimization/95729] Failure to optimize away certain returns when the condition to reach them is a calculation that already results in that value

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95729

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2020-06-18
     Ever confirmed|0                           |1

--- Comment #1 from Richard Biener <rguenth at gcc dot gnu.org> ---
Confirmed.  Sth for phiopt and/or a cond_expr match.pd pattern (which phiopt
could exercise btw).  a != b ? a - b : 0  -> a - b

[Bug tree-optimization/95729] Failure to optimize away certain returns when the condition to reach them is a calculation that already results in that value

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95729

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

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

--- Comment #2 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
;; a != b ? a - b : 0
Something like:
(simplify
 (cond (ne:c @0 @1) (minus@2 @0 @1) zero_p)
 (if (!HONOR_NANS (type) && !HONOR_SIGNED_ZEROS (type))
 @2)
(simplify
 (cond (eq:c @0 @1) zero_p (minus@2 @0 @1))
 (if (!HONOR_NANS (type) && !HONOR_SIGNED_ZEROS (type))
 @2)

Note I noticed LLVM 13 no longer does this optimization (I wonder if they have
a testsuite).

[Bug tree-optimization/95729] Failure to optimize away certain returns when the condition to reach them is a calculation that already results in that value

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95729

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

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

--- Comment #3 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
basically an exact dup of bug 19832.

*** This bug has been marked as a duplicate of bug 19832 ***