[Bug target/35498] New: libgomp/testsuite/libgomp.c/atomic-3.c fails on ppc-linux

[Bug target/35498] New: libgomp/testsuite/libgomp.c/atomic-3.c fails on ppc-linux

[jakub at gcc dot gnu dot org]

/* { dg-do run } */
/* { dg-options "-fopenmp -O2" } */

extern int omp_get_num_threads (void);
extern void abort (void);

short e[64];
int num_threads;
int g;
_Complex double d, f;

__attribute__((noinline)) void
foo (int x, long long y)
{
#pragma omp parallel num_threads (4)
  {
    int i;
    #pragma omp barrier
    for (i = 0; i < 2400; i++)
      {
        if (i == 0)
          num_threads = omp_get_num_threads ();
        #pragma omp atomic
          e[0] += x;
      }
  }
}

int
main (void)
{
  int i;
  foo (3, 3LL);
  if (e[0] != 3 * 2400 * num_threads)
    abort ();
  return 0;
}

as well as atomic-3.c fails on ppc-linux.
In *.optimized dump the atomic operation is:
  D.1288 = (short unsigned int) .omp_data_i->x;
  D.1290 = e[0];

<bb 6>:
  D.1294 = __sync_val_compare_and_swap_2 (&e, D.1290, (short int) ((short
unsigned int) D.1290 + D.1288));
  D.1295 = D.1290;
  D.1290 = D.1294;
  if (D.1294 != D.1295)
    goto <bb 6>;
  else
    goto <bb 7>;
which looks correct.


-- 
           Summary: libgomp/testsuite/libgomp.c/atomic-3.c fails on ppc-
                    linux
           Product: gcc
           Version: 4.3.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: target
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: jakub at gcc dot gnu dot org
GCC target triplet: ppc-linux


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=35498

[Bug target/35498] libgomp/testsuite/libgomp.c/atomic-3.c fails on ppc-linux

[jakub at gcc dot gnu dot org]

------- Comment #1 from jakub at gcc dot gnu dot org  2008-03-07 16:33 -------
Patch:
2008-03-07  Jakub Jelinek  <jakub@redhat.com>

        PR target/35498
        * config/rs6000/rs6000.c (rs6000_expand_compare_and_swapqhi): Shift
        wdst back after sync_compare_and_swapqhi_internal.

--- gcc/config/rs6000/rs6000.c.jj       2008-02-29 09:11:54.000000000 +0100
+++ gcc/config/rs6000/rs6000.c  2008-03-07 17:22:27.000000000 +0100
@@ -13858,6 +13858,9 @@ rs6000_expand_compare_and_swapqhi (rtx d
   emit_insn (gen_sync_compare_and_swapqhi_internal (wdst, mask,
                                                    oldval, newval, mem));

+  /* Shift the result back.  */
+  emit_insn (gen_lshrsi3 (wdst, wdst, shift));
+
   emit_move_insn (dst, gen_lowpart (mode, wdst));
 }


will test it now and if successfull, post.


-- 

jakub at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
         AssignedTo|unassigned at gcc dot gnu   |jakub at gcc dot gnu dot org
                   |dot org                     |
             Status|UNCONFIRMED                 |ASSIGNED
     Ever Confirmed|0                           |1
   Last reconfirmed|0000-00-00 00:00:00         |2008-03-07 16:33:42
               date|                            |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=35498

[Bug target/35498] libgomp/testsuite/libgomp.c/atomic-3.c fails on ppc-linux

[jakub at gcc dot gnu dot org]

------- Comment #2 from jakub at gcc dot gnu dot org  2008-03-08 07:31 -------
Subject: Bug 35498

Author: jakub
Date: Sat Mar  8 07:30:55 2008
New Revision: 133024

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=133024
Log:
        PR target/35498
        * config/rs6000/rs6000.c (rs6000_expand_compare_and_swapqhi): Shift
        wdst back after sync_compare_and_swapqhi_internal.

Modified:
    trunk/gcc/ChangeLog
    trunk/gcc/config/rs6000/rs6000.c


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=35498

[Bug target/35498] libgomp/testsuite/libgomp.c/atomic-3.c fails on ppc-linux

[jakub at gcc dot gnu dot org]

------- Comment #3 from jakub at gcc dot gnu dot org  2008-03-08 07:37 -------
Subject: Bug 35498

Author: jakub
Date: Sat Mar  8 07:36:35 2008
New Revision: 133025

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=133025
Log:
        PR target/35498
        * config/rs6000/rs6000.c (rs6000_expand_compare_and_swapqhi): Shift
        wdst back after sync_compare_and_swapqhi_internal.

Modified:
    branches/gcc-4_3-branch/gcc/ChangeLog
    branches/gcc-4_3-branch/gcc/config/rs6000/rs6000.c


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=35498

[Bug target/35498] libgomp/testsuite/libgomp.c/atomic-3.c fails on ppc-linux

[jakub at gcc dot gnu dot org]

------- Comment #4 from jakub at gcc dot gnu dot org  2008-03-08 07:48 -------
The reason why the old code without the right shift almost worked is that
for the 4 byte aligned 16-bit vars each loop was executed usually twice.
.L6:
        lha 0,0(27)
        lhz 8,2(26)
        .align 4
.L4:
        sync
        add 9,8,0
        rlwinm 10,0,0,0xffff
        rlwinm 9,9,0,0xffff
        slw 11,10,31
        slw 9,9,31
.L11:
        lwarx 7,0,29
        and 0,7,28
        cmpw 0,0,11
        bne- 0,.L12
        andc 7,7,28
        or 7,7,9
        stwcx. 7,0,29
        bne- 0,.L11
        isync
.L12:
!       srw 0,0,31      ! This insn was added by this patch
        rlwinm 0,0,0,0xffff
        cmpw 7,0,10
        extsh 0,0
        bne 7,.L4
The first time usually the atomic instruction succeeded, but r0 after rlwinm
was 0, so most often different from r10.  This means the code then jumped to
.L4, with r0 = 0 as the expected value of e[0]. r10 then becomes 0 as new
expected value, lwarx reads the new actual value of e[0], which will be
different from
the expected 0.  So it jumps to .L12, r0 now contains the e[0] value in upper
half and 0 in lower half and r10 is 0, so in the second big loop nothing is
changed and the loop exits.  This is what happens if there is no contention. 
If there is contention though, the first loop doesn't compare and swap anything
and 
as shown above, the second loop iteration won't change anything unless e[0] is
0.


-- 

jakub at gcc dot gnu dot org changed:

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


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=35498

[Bug target/35498] libgomp/testsuite/libgomp.c/atomic-3.c fails on ppc-linux

[pinskia at gcc dot gnu dot org]

-- 

pinskia at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |pinskia at gcc dot gnu dot
                   |                            |org
   Target Milestone|---                         |4.3.0


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=35498