[Bug tree-optimization/46726] New: x*x has different cost than pow(x,2) with -ffast-math

[Bug tree-optimization/46726] New: x*x has different cost than pow(x,2) with -ffast-math

[rguenth at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=46726

           Summary: x*x has different cost than pow(x,2) with -ffast-math
           Product: gcc
           Version: 4.6.0
            Status: UNCONFIRMED
          Keywords: missed-optimization
          Severity: normal
          Priority: P3
         Component: tree-optimization
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: rguenth@gcc.gnu.org
                CC: hubicka@gcc.gnu.org


double 
foo(double x, double y)
{
  return x*x + y;
}

is inlined at -O2 but not at -O2 -ffast-math (which folds x*x to pow(x, 2)).
MUL_EXPR has const 1 but __builtin_pow isn't is_inexpensive_builtin.

We probably should special-case pow(, 2) and pow(, 0.5) and sqrt where
target support is available.

[Bug tree-optimization/46726] x*x has different cost than pow(x,2) with -ffast-math

[rguenth at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=46726

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |ASSIGNED
   Last reconfirmed|                            |2010.12.06 16:29:41
         AssignedTo|unassigned at gcc dot       |rguenth at gcc dot gnu.org
                   |gnu.org                     |
     Ever Confirmed|0                           |1

--- Comment #1 from Richard Guenther <rguenth at gcc dot gnu.org> 2010-12-06 16:29:41 UTC ---
Mine.

[Bug tree-optimization/46726] x*x has different cost than pow(x,2) with -ffast-math

[rguenth at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=46726

--- Comment #2 from Richard Guenther <rguenth at gcc dot gnu.org> 2010-12-07 10:43:42 UTC ---
Author: rguenth
Date: Tue Dec  7 10:43:38 2010
New Revision: 167531

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=167531
Log:
2010-12-07  Richard Guenther  <rguenther@suse.de>

    PR tree-optimization/46726
    * tree-inline.c (estimate_num_insns): Special case pow (x, 2.0).

Modified:
    trunk/gcc/ChangeLog
    trunk/gcc/tree-inline.c

[Bug tree-optimization/46726] x*x has different cost than pow(x,2) with -ffast-math

[rguenth at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=46726

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|ASSIGNED                    |RESOLVED
         Resolution|                            |FIXED
   Target Milestone|---                         |4.6.0

--- Comment #3 from Richard Guenther <rguenth at gcc dot gnu.org> 2010-12-07 10:45:35 UTC ---
Fixed.