[Bug target/54290] New: gcc 4.4/4.5/4.6 produces wrong code on sparc with -O2

[Bug target/54290] New: gcc 4.4/4.5/4.6 produces wrong code on sparc with -O2

[eriksnga at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=54290

             Bug #: 54290
           Summary: gcc 4.4/4.5/4.6 produces wrong code on sparc with -O2
    Classification: Unclassified
           Product: gcc
           Version: 4.6.3
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: target
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: eriksnga@gmail.com


Created attachment 28031
  --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=28031
Output from gcc -v

Test system: SunOS 5.10 sun4u sparc SUNW,SPARC-Enterprise Solaris

GCC Config:  output from gcc -v is attached for version 4.6.3

########################################################################
# Test case:

# cat ./testcase.c
#define CHECK 1234567890
double vd[2] = {1., 0.};
int    vi[2] = {CHECK, 0};
double *pd = vd;
int    *pi = vi;
void init (int *n, int *dummy) __attribute__ ((noinline));
void init (int *n, int *dummy)
{
  if(0 == n) dummy[0] = 0;
}
int main ()
{
  int dummy[1532];
  int i = -1, n = 1, s = 0;
  init (&n, dummy);
  while (i < n) {
    if (i == 0) {
      if (pd[i] > 0) {
        if (pi[i] > 0) {
          s += pi[i];
#ifdef VERIFY
          return (pi[i] == CHECK? 2 : 3);
#endif
        }
      }
      pd[i] = pi[i];
    }
    ++i;
  }
  return (s == CHECK? 0 : 1);
}
# 
# gcc-4.6.3 -O2 ./testcase.c
# ./a.out; echo $?
1
# 

O1 returns expected result (exit code 0).

Problem is reproducible with gcc/g++, 32/64bit ABI with same test case 
or slight variations thereof.

Problem is not reproducible on x86_64/Linux.

########################################################################
# Results from other GCC versions:

GCC version 4.3.2: returns 0, ie. correct result
GCC version 4.4.3: returns 1, ie. wrong   result
GCC version 4.5.2: returns 1, ie. wrong   result
GCC version 4.6.1: returns 1, ie. wrong   result
GCC version 4.6.3: returns 1, ie. wrong   result
GCC version 4.7.1: returns 0, ie. correct result

On x86_64/Linux, all versions return 0.

########################################################################
# Details:

The code produced by gcc-4.6.3 misses a load (resp. contains erroneous 
instructions) resulting in the use of the address of a temp in place of 
the value stored at that address.

[..]
        fbule,pt %fcc0, .LL10
         ld     [%o7], %f8      ! %f8 <- pi[i]
        sethi   %hi(-6144), %i5 ! compute address for temp
        or      %i5, 4, %i5
        add     %i5, %fp, %i5
        st      %f8, [%i5]      ! copy from %f8 ...
        ld      [%i5], %i5      ! ... to %i5 via temp
        add     %g4, %i5, %o5   ! %o5 <- s+pi[i]
        sethi   %hi(-6144), %i5 ! recompute address of temp ...
        or      %i5, 4, %i5     ! ... which is unnecessary; but when doing so
        add     %i5, %fp, %i5   ! ... value needs to be reloaded as well:
!                               !
!       ld      [%i5], %i5      ! missing instruction
!                               !
        cmp     %i5, 0          ! supposedly (pi[i] <=> 0), except %i5 contains
!                               ! address of temp instead of its value
        movg    %icc, %o5, %g4  ! pi[i] > 0 : s <- s+pi[i]
.LL10:
        fitod   %f8, %f8
[..]

As an apparent pre-requisite, the offset for the temp needs to be too 
large to fit into an immediate constant. Any array size greater equal to 
1022(m32) resp. 1532(m64) for "dummy" in the test case seems to fit the bill.

[Bug target/54290] gcc 4.4/4.5/4.6 produces wrong code on sparc with -O2

[eriksnga at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=54290

--- Comment #1 from Erik Volk <eriksnga at gmail dot com> 2012-08-16 19:51:23 UTC ---
Created attachment 28032
  --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=28032
preprocessed test case

[Bug target/54290] [4.6 regression] wrong code at -O2 with large offset

[ebotcazou at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=54290

Eric Botcazou <ebotcazou at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Target|                            |sparc*-*-*
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2012-08-28
                 CC|                            |ebotcazou at gcc dot
                   |                            |gnu.org
      Known to work|                            |4.7.2
            Summary|gcc 4.4/4.5/4.6 produces    |[4.6 regression] wrong code
                   |wrong code on sparc with    |at -O2 with large offset
                   |-O2                         |
     Ever Confirmed|0                           |1
      Known to fail|                            |4.5.4

--- Comment #2 from Eric Botcazou <ebotcazou at gcc dot gnu.org> 2012-08-28 23:23:57 UTC ---
Confirmed (with 4.5.4 at least).

[Bug target/54290] [4.6 regression] wrong code at -O2 with large offset

[ebotcazou at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=54290

Eric Botcazou <ebotcazou at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |ASSIGNED
                 CC|ebotcazou at gcc dot        |
                   |gnu.org                     |
         AssignedTo|unassigned at gcc dot       |ebotcazou at gcc dot
                   |gnu.org                     |gnu.org

--- Comment #3 from Eric Botcazou <ebotcazou at gcc dot gnu.org> 2012-08-28 23:26:59 UTC ---
Investigating.

[Bug target/54290] [4.6 regression] wrong code at -O2 with large offset

[ebotcazou at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=54290

Eric Botcazou <ebotcazou at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                URL|                            |http://gcc.gnu.org/ml/gcc-p
                   |                            |atches/2012-09/msg00037.htm
                   |                            |l
   Target Milestone|---                         |4.6.4

[Bug target/54290] [4.6 regression] wrong code at -O2 with large offset

[ebotcazou at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=54290

--- Comment #4 from Eric Botcazou <ebotcazou at gcc dot gnu.org> 2012-09-19 15:38:20 UTC ---
Author: ebotcazou
Date: Wed Sep 19 15:38:16 2012
New Revision: 191484

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=191484
Log:
    PR rtl-optimization/54290
    * reload1.c (choose_reload_regs): Also take into account secondary MEMs
    to remove address replacements for inherited reloads.
    (replaced_subreg): Move around.

Added:
    trunk/gcc/testsuite/gcc.c-torture/execute/20120919-1.c
Modified:
    trunk/gcc/ChangeLog
    trunk/gcc/reload1.c
    trunk/gcc/testsuite/ChangeLog

[Bug target/54290] [4.6 regression] wrong code at -O2 with large offset

[ebotcazou at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=54290

Eric Botcazou <ebotcazou at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|ASSIGNED                    |RESOLVED
         Resolution|                            |FIXED
   Target Milestone|4.6.4                       |4.8.0

--- Comment #5 from Eric Botcazou <ebotcazou at gcc dot gnu.org> 2012-09-19 15:41:25 UTC ---
The fix has been installed on the mainline.  Given the very rare occurrence of
the problem and the delicate nature of the change, no backports are planned.

[Bug target/54290] [4.6 regression] wrong code at -O2 with large offset

[ebotcazou at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=54290

--- Comment #6 from Eric Botcazou <ebotcazou at gcc dot gnu.org> 2012-09-21 11:06:57 UTC ---
Author: ebotcazou
Date: Fri Sep 21 11:06:51 2012
New Revision: 191609

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=191609
Log:
    PR rtl-optimization/54290
    PR rtl-optimization/54644
    * reload1.c (choose_reload_regs): Fix thinko in previous change.

Modified:
    trunk/gcc/ChangeLog
    trunk/gcc/reload1.c