[Bug fortran/32239] New: optimize power in loops

[Bug fortran/32239] New: optimize power in loops

[jv244 at cam dot ac dot uk]

Current trunk generates always a call to 
_gfortran_pow_r4_i4 for this code

SUBROUTINE T(a,b,F,n)
 REAL :: a,b,F(n)
 INTEGER :: n
 INTEGER :: i
 DO i=1,n
    a=a+F(i)*b**i
 ENDDO
END SUBROUTINE

which could, however, be transformed by the compiler (at least in -ffast-math,
but even otherwise for Fortran) in the much more efficient equivalent code

SUBROUTINE T_opt(a,b,F,n)
 REAL :: a,b,F(n)
 INTEGER :: n
 INTEGER :: i
 REAL    :: tmp

 tmp=1.0
 DO i=1,n
    tmp=tmp*b
    a=a+F(i)*tmp
 ENDDO
END SUBROUTINE

I think it is a pretty common situation (just from grepping in our code, most
non-constant integer powers we have are loop indices).


-- 
           Summary: optimize power in loops
           Product: gcc
           Version: 4.3.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: fortran
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: jv244 at cam dot ac dot uk


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=32239

[Bug fortran/32239] optimize power in loops

[rguenth at gcc dot gnu dot org]

------- Comment #1 from rguenth at gcc dot gnu dot org  2007-06-08 10:11 -------
Confirmed.  Instead of calls to _gfortran_pow_r4_i4, gfortran should use
__builtin_powi in this case.  __builtin_powi is either expanded inline or
implemented by the libgcc powi function which looks like

TYPE
NAME (TYPE x, int m)
{
  unsigned int n = m < 0 ? -m : m;
  TYPE y = n % 2 ? x : 1;
  while (n >>= 1)
    {
      x = x * x;
      if (n % 2)
        y = y * x;
    }
  return m < 0 ? 1/y : y;
}


-- 

rguenth at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
     Ever Confirmed|0                           |1
   Last reconfirmed|0000-00-00 00:00:00         |2007-06-08 10:11:40
               date|                            |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=32239

[Bug fortran/32239] optimize power in loops, use __builtin_powi instead of _gfortran_pow_r4_i4

[jb at gcc dot gnu dot org]

------- Comment #2 from jb at gcc dot gnu dot org  2007-06-17 06:39 -------
Assigning to myself, this should be easy to fix.


-- 

jb at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |jb at gcc dot gnu dot org
         AssignedTo|unassigned at gcc dot gnu   |jb at gcc dot gnu dot org
                   |dot org                     |
             Status|NEW                         |ASSIGNED
   Last reconfirmed|2007-06-08 10:11:40         |2007-06-17 06:39:39
               date|                            |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=32239

[Bug fortran/32239] optimize power in loops, use __builtin_powi instead of _gfortran_pow_r4_i4

[patchapp at dberlin dot org]

------- Comment #3 from patchapp at dberlin dot org  2007-06-17 11:40 -------
Subject: Bug number PR32239

A patch for this bug has been added to the patch tracker.
The mailing list url for the patch is
http://gcc.gnu.org/ml/gcc-patches/2007-06/msg01172.html


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=32239

[Bug fortran/32239] optimize power in loops, use __builtin_powi instead of _gfortran_pow_r4_i4

[burnus at gcc dot gnu dot org]

------- Comment #4 from burnus at gcc dot gnu dot org  2007-06-25 19:52 -------
"At the moment the vectorizer only vectorizes builtin_pow if the exponent is
either 2 or 0.5. whereas if we expand constant exponents in the gfortran
frontend (gfc_conv_cst_int_power) it vectorizes for other constant integer
powers as well"

I've filled PR middle-end/32503 for this.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=32239

[Bug fortran/32239] optimize power in loops, use __builtin_powi instead of _gfortran_pow_r4_i4

[jb at gcc dot gnu dot org]

------- Comment #5 from jb at gcc dot gnu dot org  2007-07-01 16:24 -------
Subject: Bug 32239

Author: jb
Date: Sun Jul  1 16:24:38 2007
New Revision: 126175

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=126175
Log:
gcc/fortran:

2007-07-01  Janne Blomqvist  <jb@gcc.gnu.org>

        PR fortran/32239
        * trans-expr.c (gfc_conv_power_op): Use builtin_powi for
        real**int4 powers.
        * f95-lang.c (gfc_init_builtin_functions): Add builtin_powi to the
        builtins table.


libgfortran:

2007-07-01  Janne Blomqvist  <jb@gcc.gnu.org>

        PR fortran/32239
        * Makefile.am: Don't generate real**int4 pow functions.
        * gfortran.map: Remove real**int4 pow symbols.
        * Makefile.in: Regenerated.

testsuite

2007-07-01  Janne Blomqvist  <jb@gcc.gnu.org>

        PR fortran/32239
        * gfortran.fortran-torture/execute/intrinsic_fraction_exponent.f90
        (test_4): Use proper test for floating point equality.
        (test_8): Likewise.


Modified:
    trunk/gcc/fortran/ChangeLog
    trunk/gcc/fortran/f95-lang.c
    trunk/gcc/fortran/trans-expr.c
    trunk/gcc/testsuite/ChangeLog
   
trunk/gcc/testsuite/gfortran.fortran-torture/execute/intrinsic_fraction_exponent.f90
    trunk/libgfortran/ChangeLog
    trunk/libgfortran/Makefile.am
    trunk/libgfortran/Makefile.in
    trunk/libgfortran/gfortran.map


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=32239

[Bug fortran/32239] optimize power in loops, use __builtin_powi instead of _gfortran_pow_r4_i4

[jb at gcc dot gnu dot org]

------- Comment #6 from jb at gcc dot gnu dot org  2007-07-02 16:21 -------
Subject: Bug 32239

Author: jb
Date: Mon Jul  2 16:21:37 2007
New Revision: 126215

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=126215
Log:
Forgot to delete these during yesterdays commit.

2007-07-02  Janne Blomqvist  <jb@gcc.gnu.org>

        PR fortran/32239
        * generated/pow_r*_i4.c: Removed.


Removed:
    trunk/libgfortran/generated/pow_r10_i4.c
    trunk/libgfortran/generated/pow_r16_i4.c
    trunk/libgfortran/generated/pow_r4_i4.c
    trunk/libgfortran/generated/pow_r8_i4.c
Modified:
    trunk/libgfortran/ChangeLog


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=32239

[Bug fortran/32239] optimize power in loops, use __builtin_powi instead of _gfortran_pow_r4_i4

[jb at gcc dot gnu dot org]

------- Comment #7 from jb at gcc dot gnu dot org  2007-07-02 20:46 -------
Closing as Fortran FE is fixed. There is 32503 for better vectorization of
builtin_powi, and if we want the strength reduction optimization from comment
#0 a new missed-optimization PR should be filed against the middle-end (or
tree-optimization).


-- 

jb at gcc dot gnu dot org changed:

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


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=32239