[Bug tree-optimization/51877] New: [4.7 Regression] XEmacs miscompilation due to tail merging

[Bug tree-optimization/51877] New: [4.7 Regression] XEmacs miscompilation due to tail merging

[jakub at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51877

             Bug #: 51877
           Summary: [4.7 Regression] XEmacs miscompilation due to tail
                    merging
    Classification: Unclassified
           Product: gcc
           Version: 4.7.0
            Status: UNCONFIRMED
          Keywords: wrong-code
          Severity: normal
          Priority: P3
         Component: tree-optimization
        AssignedTo: jakub@gcc.gnu.org
        ReportedBy: jakub@gcc.gnu.org
                CC: vries@gcc.gnu.org


extern void abort (void);
struct A { int a; char b[32]; } a, b;

__attribute__((noinline, noclone))
struct A
bar (int x)
{
  struct A r;
  static int n;
  r.a = ++n;
  __builtin_memset (r.b, 0, sizeof (r.b));
  r.b[0] = x;
  return r;
}

__attribute__((noinline, noclone))
void
baz (void)
{
  asm volatile ("" : : : "memory");
}

__attribute__((noinline, noclone))
void
foo (struct A *x, int y)
{
  if (y == 6)
    a = bar (7);
  else
    *x = bar (7);
  baz ();
}

int
main ()
{
  a = bar (3);
  b = bar (4);
  if (a.a != 1 || a.b[0] != 3 || b.a != 2 || b.b[0] != 4)
    abort ();
  foo (&b, 0);
  if (a.a != 1 || a.b[0] != 3 || b.a != 3 || b.b[0] != 7)
    abort ();
  foo (&b, 6);
  if (a.a != 4 || a.b[0] != 7 || b.a != 3 || b.b[0] != 7)
    abort ();
  return 0;
}

is miscompiled at -O2 (distilled from XEmacs).  Tail merging surprisingly
decides to tail merge the two calls, eventhough they have different lhs.

[Bug tree-optimization/51877] [4.7 Regression] XEmacs miscompilation due to tail merging

[jakub at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51877

--- Comment #1 from Jakub Jelinek <jakub at gcc dot gnu.org> 2012-01-17 07:49:33 UTC ---
Created attachment 26346
  --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=26346
gcc47-pr51877.patch

Untested fix.

[Bug tree-optimization/51877] [4.7 Regression] XEmacs miscompilation due to tail merging

[rguenth at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51877

Richard Guenther <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |ASSIGNED
   Last reconfirmed|                            |2012-01-17
   Target Milestone|---                         |4.7.0
     Ever Confirmed|0                           |1

--- Comment #2 from Richard Guenther <rguenth at gcc dot gnu.org> 2012-01-17 10:14:15 UTC ---
Patch is ok.

[Bug tree-optimization/51877] [4.7 Regression] XEmacs miscompilation due to tail merging

[jakub at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51877

--- Comment #3 from Jakub Jelinek <jakub at gcc dot gnu.org> 2012-01-17 10:38:43 UTC ---
Author: jakub
Date: Tue Jan 17 10:38:38 2012
New Revision: 183237

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=183237
Log:
    PR tree-optimization/51877
    * tree-ssa-tail-merge.c (gimple_equal_p): Don't return true whenever
    call arguments and fndecls compare equal, instead return false if they
    don't.  Return true only if lhs1 and lhs2 are either both NULL, or
    both SSA_NAMEs that are valueized the same, or they satisfy
    operand_equal_p.

    * gcc.c-torture/execute/pr51877.c: New test.

Added:
    trunk/gcc/testsuite/gcc.c-torture/execute/pr51877.c
Modified:
    trunk/gcc/ChangeLog
    trunk/gcc/testsuite/ChangeLog
    trunk/gcc/tree-ssa-tail-merge.c

[Bug tree-optimization/51877] [4.7 Regression] XEmacs miscompilation due to tail merging

[jakub at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51877

Jakub Jelinek <jakub at gcc dot gnu.org> changed:

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

--- Comment #4 from Jakub Jelinek <jakub at gcc dot gnu.org> 2012-01-17 11:07:51 UTC ---
Fixed.