[Bug fortran/28914] New: Code inside loop hangs; outside loop runs normally; runs OK on other compilers

[Bug fortran/28914] New: Code inside loop hangs; outside loop runs normally; runs OK on other compilers

[kornkven at arsc dot edu]

!
! Un-comment the DO and ENDDO and the compiled program
! hangs after the first output line.
!
! Compiled with: gfortran junk.f90
! where: gfortran --version gives
!   GNU Fortran 95 (GCC 4.0.2 20051125 (Red Hat 4.0.2-8))
! Running on Fedora Core 4, Opteron
!
! E. Kornkven, kornkven@arsc.edu
!
      program junk
      implicit none
      integer n, i
      parameter (n = 1000000)
      double precision a(n), b(n), c(n), summation

      print*, '                perform some computation ... '
      summation = 0.0
      do i = 1, 1
         a = (/ (i, i = 1, n) /)
         a = sqrt(a)
         b = 1.0 / a
         c = b - a
         summation = SUM(a)
      enddo

      a(n/2) = 13.0
      print*, "Is the middle value 13.0? ", a(n/2-1), a(n/2), a(n/2+1)
      print*, "Summation = ", summation

      end program junk


-- 
           Summary: Code inside loop hangs; outside loop runs normally; runs
                    OK on other compilers
           Product: gcc
           Version: 4.0.2
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: fortran
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: kornkven at arsc dot edu


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=28914

[Bug fortran/28914] Code inside loop hangs; outside loop runs normally; runs OK on other compilers

[kargl at gcc dot gnu dot org]

------- Comment #1 from kargl at gcc dot gnu dot org  2006-08-31 02:06 -------
Upgrade gfortran to at least 4.1.1.  The code works
fine with gfortran 4.2.


-- 

kargl at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |WAITING


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=28914

[Bug fortran/28914] Code inside loop hangs; outside loop runs normally; runs OK on other compilers

[kargl at gcc dot gnu dot org]

------- Comment #2 from kargl at gcc dot gnu dot org  2006-08-31 02:47 -------
Well, you do need to upgrade your compiler, but there appears to be
a bug :(

If n <= 65000, the program works fine.  For larger n, the combination
of 
      do i = 1, 1
         a = (/ (i, i = 1, n) /)
      end do

i as the do-loop index and i as the implied-do-loop index is
causing problems.  Normally, one cannot alter the do-loop 
index within the body of the loop.  ISTR from the F95 standard,
that the i in the implied-do-loop has the scope of only the
implied-do-loop.  Thus, the above code is legal.

Why there is a change in behavior at i = 65000 (or so), I have
no idea.


-- 

kargl at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Last reconfirmed|0000-00-00 00:00:00         |2006-08-31 02:47:50
               date|                            |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=28914

[Bug fortran/28914] Code inside loop hangs; outside loop runs normally; runs OK on other compilers

[jvdelisle at gcc dot gnu dot org]

------- Comment #3 from jvdelisle at gcc dot gnu dot org  2006-08-31 05:28 -------
Setting the parameter n=65535, the program appears to execute correctly. 
However, the pr28914.f90.003t.original file is 706800 bytes long and embedded
with a very large static declaration of the array.  As if it has been inlined.

With n=66536, the dump file is 4436 bytes long and has code to initialize the
array with a loop.  That looping code appears broken.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=28914

[Bug fortran/28914] Code inside loop hangs; outside loop runs normally; runs OK on other compilers

[paul dot richard dot thomas at cea dot fr]

------- Comment #4 from paul dot richard dot thomas at cea dot fr  2006-09-01 13:45 -------
(In reply to comment #3)
> Setting the parameter n=65535, the program appears to execute correctly. 
> However, the pr28914.f90.003t.original file is 706800 bytes long and embedded
> with a very large static declaration of the array.  As if it has been inlined.
> With n=66536, the dump file is 4436 bytes long and has code to initialize the
> array with a loop.  That looping code appears broken.

The looping code, of itself, is not broken.  If one of the 'i's, say in the
implied do-loop, is changed to 'j', the code runs to completion.  The problem
is that the implied do-loop counter uses a variable declaration and so a
symbol.  This clashes with the variable i.

Since do-loops can run with +ve or -ve steps, the end condition is enforced
through:

            L.1:;
            D.931 = i == 1;
            i = i + 1;
            if (D.931) goto L.2; else (void) 0;

ie. with an equality.  The implied do-loop sets this larger than 1 so the loop
never stops.

For n < 65536, the loop is simplified out of existence and the large static
array makes its appearance.  This seems to be an undesirable consequence of
treating array initializers and array constructors with the same limit.

I would:

(i) Change the size limit for simplification of array constructors; and
(ii) Store the current value of the loop counter in a temporary and restore it
after the array constructor has done its thing (patch follows).

Paul


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=28914

[Bug fortran/28914] Code inside loop hangs; outside loop runs normally; runs OK on other compilers

[paul dot richard dot thomas at cea dot fr]

------- Comment #5 from paul dot richard dot thomas at cea dot fr  2006-09-01 13:48 -------
Created an attachment (id=12168)
 --> (http://gcc.gnu.org/bugzilla/attachment.cgi?id=12168&action=view)
A provisional fix for the problem

This is not regtested.

Also, I know that there is a better way to detect a declared variable; however,
I am up to my eyeballs getting TR15541 out of the door... wait a few days, I
will sort this one.

Paul


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=28914

[Bug fortran/28914] Code inside loop hangs; outside loop runs normally; runs OK on other compilers

[jvdelisle at gcc dot gnu dot org]

------- Comment #6 from jvdelisle at gcc dot gnu dot org  2006-09-02 19:24 -------
I tested the provisional patch on i686-linux-pc-gnu.  

Had to set tmp_loopvar = NULL when declared to avoid warning message on
possibly uninitialized variable.

Fixes the test case in this PR.  Regression testsd fine.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=28914

[Bug fortran/28914] Code inside loop hangs; outside loop runs normally; runs OK on other compilers

[jvdelisle at gcc dot gnu dot org]

------- Comment #7 from jvdelisle at gcc dot gnu dot org  2006-09-03 03:44 -------
Just an added note.  Compile time for large values of n is very long.  Many
seconds.  For n - 20000000

$ time gfc pr28914.f90

real    1m5.009s
user    1m3.896s
sys     0m0.048s

This is on 3.2 gigahertz machine.  The resulting executable is about 10kbytes
in size.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=28914

[Bug fortran/28914] Code inside loop hangs; outside loop runs normally; runs OK on other compilers

[paul dot richard dot thomas at cea dot fr]

------- Comment #8 from paul dot richard dot thomas at cea dot fr  2006-09-04 12:08 -------
Even simpler is:

trans-array.c(gfc_trans_array_constructor_value)

replace           loopvar = se.expr;
by                loopvar = gfc_evaluate_now (se.expr, pblock);

gfc_expand_constructor is called from resolve_expr and from three places in
expr.c.  As far as I can tell, non-initialization expressions only try the
expansion from resolve_expr.  If I flag the calls to distinguish them and limit
the maximum number of expanded elements to 10, say, in gfc_expand_constructor,
the code reflects this but the compilation time does not.  Something, somewhere
is doing a temporary expansion of the constructor, which is taking all the
time.

I have to leave this again but I will get to the bottom of it.

Paul


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=28914

[Bug fortran/28914] Code inside loop hangs; outside loop runs normally; runs OK on other compilers

[jvdelisle at gcc dot gnu dot org]

------- Comment #9 from jvdelisle at gcc dot gnu dot org  2006-09-04 19:33 -------
The proposed change in comment #8 appears to give several testsuite failures.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=28914

[Bug fortran/28914] Code inside loop hangs; outside loop runs normally; runs OK on other compilers

[pault at gcc dot gnu dot org]

------- Comment #10 from pault at gcc dot gnu dot org  2006-09-05 19:38 -------
(In reply to comment #9)
> The proposed change in comment #8 appears to give several testsuite failures.
> 
Yes, I know; see the email that I sent you today.  The original patch on #5
works fine and is nearly the right solution.

Paul


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=28914

[Bug fortran/28914] Code inside loop hangs; outside loop runs normally; runs OK on other compilers

[jvdelisle at gcc dot gnu dot org]

------- Comment #11 from jvdelisle at gcc dot gnu dot org  2006-09-10 04:18 -------
Apatch for this bug has been submitted to the fortran list for approval.


-- 

jvdelisle at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
         AssignedTo|unassigned at gcc dot gnu   |jvdelisle at gcc dot gnu dot
                   |dot org                     |org
             Status|WAITING                     |ASSIGNED
     Ever Confirmed|0                           |1
   Last reconfirmed|2006-08-31 02:47:50         |2006-09-10 04:18:51
               date|                            |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=28914

[Bug fortran/28914] Code inside loop hangs; outside loop runs normally; runs OK on other compilers

[jvdelisle at gcc dot gnu dot org]

------- Comment #12 from jvdelisle at gcc dot gnu dot org  2006-09-10 04:53 -------
Subject: Bug 28914

Author: jvdelisle
Date: Sun Sep 10 04:53:18 2006
New Revision: 116808

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=116808
Log:
2006-09-09  Paul Thomas <pault@gcc.gnu.org>

        PR fortran/28914
        * trans-array.c (gfc_trans_array_constructor_value): Create a temporary
        loop variable to hold the current loop variable in case it is modified
        by the array constructor.

Modified:
    trunk/gcc/fortran/ChangeLog
    trunk/gcc/fortran/trans-array.c


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=28914

[Bug fortran/28914] Code inside loop hangs; outside loop runs normally; runs OK on other compilers

[jvdelisle at gcc dot gnu dot org]

------- Comment #13 from jvdelisle at gcc dot gnu dot org  2006-09-10 04:58 -------
Subject: Bug 28914

Author: jvdelisle
Date: Sun Sep 10 04:58:29 2006
New Revision: 116809

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=116809
Log:
2006-09-09  Jerry DeLisle  <jvdelisle@gcc.gnu.org>

        PR fortran/28914
        * gfortran.dg/actual_array_constructor_3.f90: New test.

Added:
    trunk/gcc/testsuite/gfortran.dg/actual_array_constructor_3.f90
Modified:
    trunk/gcc/testsuite/ChangeLog


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=28914

[Bug fortran/28914] Code inside loop hangs; outside loop runs normally; runs OK on other compilers

[jvdelisle at gcc dot gnu dot org]

------- Comment #14 from jvdelisle at gcc dot gnu dot org  2006-09-10 05:07 -------
Fixed on 4.2 only, Follow PR20923 for long compile time issues.


-- 

jvdelisle at gcc dot gnu dot org changed:

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


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=28914

[Bug fortran/28914] Code inside loop hangs; outside loop runs normally; runs OK on other compilers

[pinskia at gcc dot gnu dot org]

-- 

pinskia at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|---                         |4.2.0


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=28914