[Bug optimization/14705] New: [tree-ssa] more alias analysis needed!?

[Bug optimization/14705] New: [tree-ssa] more alias analysis needed!?

[kazu at cs dot umass dot edu]

The second "if" statement is not optimized away until CSE.

/* Reduced from reload_combine() in postreload.c.  */

struct s {
  int c;
  struct s *next;
};

int global;

extern void bar (void);

void
foo (struct s *p)
{
  for (; p; p = p->next)
    {
      if (p->c != 0)
	continue;

      global++;
      if (p->c == 0)
	bar ();
    }
}

To give you sense of where this comes from,
think of the first "if" as !INSN_P and
think of the second one as INSN_P with bar() being single_set_2.

-- 
           Summary: [tree-ssa] more alias analysis needed!?
           Product: gcc
           Version: tree-ssa
            Status: UNCONFIRMED
          Severity: enhancement
          Priority: P2
         Component: optimization
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: kazu at cs dot umass dot edu
                CC: gcc-bugs at gcc dot gnu dot org


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=14705

[Bug optimization/14705] [tree-ssa] more alias analysis needed!?

[pinskia at gcc dot gnu dot org]

------- Additional Comments From pinskia at gcc dot gnu dot org  2004-03-24 04:34 -------
Confirmed,
Variable: p, UID 1, type memory tag: TMT.3, default def: p_5
Variable: TMT.3, UID 5, is global, call clobbered, may aliases: { global }

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
     Ever Confirmed|                            |1
           Keywords|                            |pessimizes-code
   Last reconfirmed|0000-00-00 00:00:00         |2004-03-24 04:34:59
               date|                            |
   Target Milestone|---                         |tree-ssa


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=14705

[Bug optimization/14705] [tree-ssa] more alias analysis needed!?

[kazu at cs dot umass dot edu]

------- Additional Comments From kazu at cs dot umass dot edu  2004-03-24 17:30 -------
Reduced to:

struct s {
  int c;
  struct s *next;
};

int global;

extern void bar (void);

void
foo (struct s *p)
{
  if (p->c != 0)
    return;

  global++;
  if (p->c == 0)
    bar ();
}

-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=14705

[Bug optimization/14705] [tree-ssa] more alias analysis needed!?

[kazu at cs dot umass dot edu]

------- Additional Comments From kazu at cs dot umass dot edu  2004-03-24 17:32 -------
Another similar testcase reduced from web.c.

extern void abort (void) __attribute__ ((__noreturn__));

struct s {
  int a;
  int b;
};

void
bar (struct s *p)
{
  if (p->a)
    abort ();

  p->b = 0;

  if (p->a)
    abort ();
}


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=14705

[Bug optimization/14705] [tree-ssa] more alias analysis needed!?

[pinskia at gcc dot gnu dot org]

------- Additional Comments From pinskia at gcc dot gnu dot org  2004-03-24 17:36 -------
The reduced case from web.c is also PR 13761.

-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=14705

[Bug tree-optimization/14705] [tree-ssa] more alias analysis needed!?

[pinskia at gcc dot gnu dot org]

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|3.5.0                       |---


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=14705

[Bug tree-optimization/14705] [tree-ssa] more alias analysis needed!?

[steven at gcc dot gnu dot org]

------- Additional Comments From steven at gcc dot gnu dot org  2004-12-30 14:05 -------
Looks like food for DannyB.

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |dberlin at gcc dot gnu dot
                   |                            |org


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=14705

[Bug tree-optimization/14705] [tree-ssa] more alias analysis needed!?

[kazu at cs dot umass dot edu]

------- Additional Comments From kazu at cs dot umass dot edu  2005-05-07 15:03 -------
FWIW, here is the last SSA form I get with vops.

foo (p)
{
  int D.1241;
  int global.0;
  int D.1239;

<bb 0>:
  #   VUSE <global_3>;
  D.1239_2 = p_1->c;
  if (D.1239_2 != 0) goto <L2>; else goto <L0>;

<L0>:;
  #   VUSE <global_3>;
  global.0_4 = global;
  D.1241_5 = global.0_4 + 1;
  #   global_6 = V_MUST_DEF <global_3>;
  global = D.1241_5;
  #   VUSE <global_6>;
  D.1239_7 = p_1->c;
  if (D.1239_7 == 0) goto <L1>; else goto <L2>;

<L1>:;
  #   global_8 = V_MAY_DEF <global_6>;
  bar () [tail call];

<L2>:;
  return;

}


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=14705