[Bug fortran/46331] New: Compilation time long with simple function in array constructor

[Bug fortran/46331] New: Compilation time long with simple function in array constructor

[jvdelisle at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=46331

           Summary: Compilation time long with simple function in array
                    constructor
           Product: gcc
           Version: 4.6.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: fortran
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: jvdelisle@gcc.gnu.org


program foo
    implicit none

    Integer :: i
    Integer, Parameter :: N = 10**4
    Real, Dimension(N) :: xs

    ! Random points
    xs = (/ (rand(0), i=1,N) /)
    print *, xs
end program

The time spent in the FE is not bad, but the resulting translation is horrible
and it wreaks havoc with the middle end and down the road.

I think we should not expand this constructor at all, especially since 'i' is
not used in the function expression. However, rand(0) needs to be called once
for each element.  That means it needs to be translated into:

do i-1,N
  xs = rand(0)
end do

In otherwords, I think another special case in gfc_trans_assignment.  There are
other special cases already there.

[Bug fortran/46331] Compilation time long with simple function in array constructor

[jvdelisle at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=46331

--- Comment #1 from Jerry DeLisle <jvdelisle at gcc dot gnu.org> 2010-11-06 16:09:30 UTC ---
I should add that if rand is the only function that acts like this, then this
is not of much value.  While just playing around, this translates as expected.
(Nice short -fdump-tree-original file.)

program foo
    implicit none

    Integer :: i
    Integer, Parameter :: N = 10**4
    Real, Dimension(N) :: xs

    ! Random points
    !xs = (/ (rand(0), i=1,N) /)
    xs = (/ (myfunction(0), i=1,N) /)
    !xs = myfunction (0.0)
    print *, xs
contains
  function myfunction(somenumber)
    integer :: somenumber
    real :: myfunction
    myfunction = 1234.567
    if (somenumber .eq. 42) return
    myfunction = somenumber + rand(0)
  end function
end program

[Bug fortran/46331] Compilation time long with simple function in array constructor

[jvdelisle at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=46331

--- Comment #2 from Jerry DeLisle <jvdelisle at gcc dot gnu.org> 2010-11-07 14:32:47 UTC ---
Patch: The part removed too agressively decides if an expression is constant. 
In the case of rand(), the result obviously does not reduce to a constant but
the array constructor was expanded.  Returning zero here means the function is
not constant and therefore the array is not expanded at compile time.

Regression tested OK on x86-64.

Index: expr.c
===================================================================
--- expr.c    (revision 166382)
+++ expr.c    (working copy)
@@ -900,7 +900,6 @@ int
 gfc_is_constant_expr (gfc_expr *e)
 {
   gfc_constructor *c;
-  gfc_actual_arglist *arg;

   if (e == NULL)
     return 1;
@@ -921,19 +920,8 @@ gfc_is_constant_expr (gfc_expr *e)
       /* Specification functions are constant.  */
       if (check_specification_function (e) == MATCH_YES)
     return 1;
+      return 0;

-      /* Call to intrinsic with at least one argument.  */
-      if (e->value.function.isym && e->value.function.actual)
-    {
-      for (arg = e->value.function.actual; arg; arg = arg->next)
-        if (!gfc_is_constant_expr (arg->expr))
-          return 0;
-
-      return 1;
-    }
-      else
-    return 0;
-
     case EXPR_CONSTANT:
     case EXPR_NULL:
       return 1;

[Bug fortran/46331] Compilation time long with simple function in array constructor

[jvdelisle at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=46331

Jerry DeLisle <jvdelisle at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |ASSIGNED
   Last reconfirmed|                            |2010.11.08 02:19:56
         AssignedTo|unassigned at gcc dot       |jvdelisle at gcc dot
                   |gnu.org                     |gnu.org
     Ever Confirmed|0                           |1

--- Comment #3 from Jerry DeLisle <jvdelisle at gcc dot gnu.org> 2010-11-08 02:19:56 UTC ---
I have a better patch and will submit it for approval.

[Bug fortran/46331] Compilation time long with simple function in array constructor

[jvdelisle at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=46331

--- Comment #4 from Jerry DeLisle <jvdelisle at gcc dot gnu.org> 2010-11-10 04:58:23 UTC ---
Author: jvdelisle
Date: Wed Nov 10 04:58:16 2010
New Revision: 166520

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=166520
Log:
2010-11-09  Jerry DeLisle  <jvdelisle@gcc.gnu.org>
        Mikael Morin   <mikael@gcc.gnu.org>

    PR fortran/46331
    * intrinsic.c: Correctly set the pure attributes for intrinsic
    functions.
    * expr.c (check_specification_function): Remove this function and move
    its code into gfc_is_constant_expr. (gfc_is_constant_expr): Change the
    order of checks by checking for non-constant arguments first.  Then,
    check for initialization functions, followed by intrinsics.

Modified:
    trunk/gcc/fortran/ChangeLog
    trunk/gcc/fortran/expr.c
    trunk/gcc/fortran/intrinsic.c

[Bug fortran/46331] Compilation time long with simple function in array constructor

[jvdelisle at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=46331

Jerry DeLisle <jvdelisle at gcc dot gnu.org> changed:

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

--- Comment #5 from Jerry DeLisle <jvdelisle at gcc dot gnu.org> 2010-11-10 05:25:59 UTC ---
Fixed on trunk.