[Bug fortran/38318] New: moving the allocation of temps out of loops.

[Bug fortran/38318] New: moving the allocation of temps out of loops.

[jv244 at cam dot ac dot uk]

consider the following source and timings, were a natural form of a subroutine
S1, and two hand optimized forms are timed:

> cat test.f90
SUBROUTINE S1(N,A)
 REAL :: A(3)
 DO I=1,N
   CALL S2(-A)
 ENDDO
END SUBROUTINE

SUBROUTINE S1_opt1(N,A)
 REAL :: A(3)
 REAL, ALLOCATABLE :: B(:)
 ALLOCATE(B(SIZE(A,1)))
 DO I=1,N
   B=-A
   CALL S2(B)
 ENDDO
END SUBROUTINE


SUBROUTINE S1_opt2(N,A)
 REAL :: A(3),B(3)
 DO I=1,N
   B=-A
   CALL S2(B)
 ENDDO
END SUBROUTINE

> cat main.f90

SUBROUTINE S2(A)
 REAL :: A(*),D
 COMMON /F/D
 D=D+A(1)+A(2)+A(3)
END SUBROUTINE

INTEGER, PARAMETER :: N=100000
REAL :: A(3),T1,T2,T3,T4,D
COMMON /F/D
D=0.0
A=0.0
CALL CPU_TIME(T1)
DO I=1,10000
  CALL S1(N,A)
ENDDO
CALL CPU_TIME(T2)
DO I=1,10000
  CALL S1_opt1(N,A)
ENDDO
CALL CPU_TIME(T3)
DO I=1,10000
  CALL S1_opt2(N,A)
ENDDO
CALL CPU_TIME(T4)

write(6,*) "Default [s]:",T2-T1
write(6,*) "OPT1 [s]:",T3-T2
write(6,*) "OPT2 [s]:",T4-T3
write(6,*) D
END

gfortran-4.4 -O3 test.f90 main.f90
 Default [s]:   18.293142
 OPT1 [s]:   6.2603912
 OPT2 [s]:   6.2563915

ifort -O3 test.f90 main.f90
 Default [s]:   6.256391
 OPT1 [s]:   6.252390
 OPT2 [s]:   6.256390

so, gfortran by default is about 3x slower than ifort, which by default moves
the generation of the temporaries out of the loop. 

FYI, allowing for multi file IPO, I hope LTO gets that far...

ifort -O3 -fast test.f90 main.f90 (includes ipo)
 Default [s]:   3.752234
 OPT1 [s]:   1.276080
 OPT2 [s]:   3.752234


-- 
           Summary: moving the allocation of temps out of loops.
           Product: gcc
           Version: 4.4.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: fortran
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: jv244 at cam dot ac dot uk
OtherBugsDependingO 36854
             nThis:


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=38318

[Bug fortran/38318] moving the allocation of temps out of loops.

[tkoenig at gcc dot gnu dot org]

------- Comment #1 from tkoenig at gcc dot gnu dot org  2008-12-06 20:25 -------
This could also be useful when done in the middle-end,
see PR 21046.


-- 

tkoenig at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
  BugsThisDependsOn|                            |21046
           Severity|normal                      |enhancement
             Status|UNCONFIRMED                 |NEW
     Ever Confirmed|0                           |1
   Last reconfirmed|0000-00-00 00:00:00         |2008-12-06 20:25:54
               date|                            |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=38318

[Bug fortran/38318] moving the allocation of temps out of loops.

[jv244 at cam dot ac dot uk]

------- Comment #2 from jv244 at cam dot ac dot uk  2010-02-21 09:12 -------
seemingly being discussed, since useful for tonto

http://gcc.gnu.org/ml/fortran/2010-02/msg00157.html


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=38318

[Bug fortran/38318] moving the allocation of temps out of loops.

[burnus at gcc dot gnu dot org]

------- Comment #3 from burnus at gcc dot gnu dot org  2010-02-21 11:06 -------
(In reply to comment #2)
> seemingly being discussed, since useful for tonto
> 
> http://gcc.gnu.org/ml/fortran/2010-02/msg00157.html
> 

But there: "it's unfortunately not possible to avoid the temporary creation
without serious data-flow analysis work - too late for the frontend"

Thus, this seems to be more a middle-end item.

Regarding the current timing, I get with ifort -O3 -fast (v 11.1) vs.
gfortran -flto -fwhole-program -O3 --fast-math -march=native (today's 4.5) It
is also interesting that gfortran is much faster for the optimized version than
ifort.

gfortran                     ifort
 Default [s]:   24.881554     Default [s]:   5.108319
 OPT1 [s]:   1.6641045        OPT1 [s]:   3.280205
 OPT2 [s]:   1.6641045        OPT2 [s]:   4.988311
   0.0000000                   0.0000000E+00

real    0m28.420s            real    0m13.400s


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=38318

[Bug middle-end/38318] moving the allocation of temps out of loops.

[jv244 at cam dot ac dot uk]

------- Comment #4 from jv244 at cam dot ac dot uk  2010-02-21 12:11 -------
(In reply to comment #3)
> (In reply to comment #2)
> > seemingly being discussed, since useful for tonto
> > 
> > http://gcc.gnu.org/ml/fortran/2010-02/msg00157.html
> > 
> 
> But there: "it's unfortunately not possible to avoid the temporary creation
> without serious data-flow analysis work - too late for the frontend"
> 
> Thus, this seems to be more a middle-end item.

right, changing component as such. This would actually be much more powerful as
a middle-end thing, since it would also capture the case where a programmer
would explicitly allocate/deallocate stuff in a loop.


-- 

jv244 at cam dot ac dot uk changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
          Component|fortran                     |middle-end


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=38318