Re: [PATCH 3/5] IPA ICF pass

[Joey Ye <joey.ye.cc@gmail.com>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63747 is likely caused by
this patch. compare_gimple_switch does not check CASE_LOW and
CASE_HIGH, resulting merging functions not identical.

Interestingly in the first a few versions of this patch CASE_LOW/HIGH
were checked. But last versions only checks CASE_LABEL. What was the
intention?

Thanks,
Joey

On Thu, Oct 23, 2014 at 5:18 AM, Jiong Wang
<wong.kwongyuan.tools@gmail.com> wrote:
> PR 63574 ICE building libjava (segfault) on arm-linux-gnueabihf is
> caused by this commit.
>
> from the backtrace, the ICF pass is trying to compare two label tree
> node without type info.
>
> while looks like "compare_operand" expect the type info always be not
> empty before invoking "func_checker::compatible_types_p".
>
> I think we should add a similiar t1/t2 check at the start of
> "func_checker::compatible_types_p", just
> like what has been done at the head of "func_checker::compare_operand".
>
> And I verified if we add that check, the crash gone away.
>
> Regards,
> Jiong
>
>
> 2014-10-15 18:03 GMT+01:00 Martin Liška <mliska@suse.cz>:
>> On 10/14/2014 06:04 PM, Jan Hubicka wrote:
>>>>
>>>> diff --git a/gcc/cgraph.h b/gcc/cgraph.h
>>>> index fb41b01..2de98b4 100644
>>>> --- a/gcc/cgraph.h
>>>> +++ b/gcc/cgraph.h
>>>> @@ -172,6 +172,12 @@ public:
>>>>     /* Dump referring in list to FILE.  */
>>>>     void dump_referring (FILE *);
>>>>
>>>> +  /* Get number of references for this node.  */
>>>> +  inline unsigned get_references_count (void)
>>>> +  {
>>>> +    return ref_list.references ? ref_list.references->length () : 0;
>>>> +  }
>>>
>>>
>>> Probably better called num_references() (like we have num_edge in
>>> basic-block.h)
>>>>
>>>> @@ -8068,6 +8069,19 @@ it may significantly increase code size
>>>>   (see @option{--param ipcp-unit-growth=@var{value}}).
>>>>   This flag is enabled by default at @option{-O3}.
>>>>
>>>> +@item -fipa-icf
>>>> +@opindex fipa-icf
>>>> +Perform Identical Code Folding for functions and read-only variables.
>>>> +The optimization reduces code size and may disturb unwind stacks by
>>>> replacing
>>>> +a function by equivalent one with a different name. The optimization
>>>> works
>>>> +more effectively with link time optimization enabled.
>>>> +
>>>> +Nevertheless the behavior is similar to Gold Linker ICF optimization,
>>>> GCC ICF
>>>> +works on different levels and thus the optimizations are not same -
>>>> there are
>>>> +equivalences that are found only by GCC and equivalences found only by
>>>> Gold.
>>>> +
>>>> +This flag is enabled by default at @option{-O2}.
>>>
>>> ... and -Os?
>>>>
>>>> +    case ARRAY_REF:
>>>> +    case ARRAY_RANGE_REF:
>>>> +      {
>>>> +       x1 = TREE_OPERAND (t1, 0);
>>>> +       x2 = TREE_OPERAND (t2, 0);
>>>> +       y1 = TREE_OPERAND (t1, 1);
>>>> +       y2 = TREE_OPERAND (t2, 1);
>>>> +
>>>> +       if (!compare_operand (array_ref_low_bound (t1),
>>>> +                             array_ref_low_bound (t2)))
>>>> +         return return_false_with_msg ("");
>>>> +       if (!compare_operand (array_ref_element_size (t1),
>>>> +                             array_ref_element_size (t2)))
>>>> +         return return_false_with_msg ("");
>>>> +       if (!compare_operand (x1, x2))
>>>> +         return return_false_with_msg ("");
>>>> +       return compare_operand (y1, y2);
>>>> +      }
>>>
>>>
>>> No need for {...} if there are no local vars.
>>>>
>>>> +bool
>>>> +func_checker::compare_function_decl (tree t1, tree t2)
>>>> +{
>>>> +  bool ret = false;
>>>> +
>>>> +  if (t1 == t2)
>>>> +    return true;
>>>> +
>>>> +  symtab_node *n1 = symtab_node::get (t1);
>>>> +  symtab_node *n2 = symtab_node::get (t2);
>>>> +
>>>> +  if (m_ignored_source_nodes != NULL && m_ignored_target_nodes != NULL)
>>>> +    {
>>>> +      ret = m_ignored_source_nodes->contains (n1)
>>>> +           && m_ignored_target_nodes->contains (n2);
>>>> +
>>>> +      if (ret)
>>>> +       return true;
>>>> +    }
>>>> +
>>>> +  /* If function decl is WEAKREF, we compare targets.  */
>>>> +  cgraph_node *f1 = cgraph_node::get (t1);
>>>> +  cgraph_node *f2 = cgraph_node::get (t2);
>>>> +
>>>> +  if(f1 && f2 && f1->weakref && f2->weakref)
>>>> +    ret = f1->alias_target == f2->alias_target;
>>>> +
>>>> +  return ret;
>>>
>>>
>>> Comparing aliases is bit more complicated than just handling weakrefs. I
>>> have
>>> patch for symtab_node::equivalent_address_p somewhre in queue.  lets just
>>> drop
>>> the fancy stuff for the moment and compare f1&&f2 for equivalence.
>>>>
>>>> +  ret = compare_decl (t1, t2);
>>>
>>>
>>> Why functions are not compared with compare_decl while variables are?
>>>>
>>>> +
>>>> +  return return_with_debug (ret);
>>>> +}
>>>> +
>>>> +void
>>>> +func_checker::parse_labels (sem_bb *bb)
>>>> +{
>>>> +  for (gimple_stmt_iterator gsi = gsi_start_bb (bb->bb); !gsi_end_p
>>>> (gsi);
>>>> +       gsi_next (&gsi))
>>>> +    {
>>>> +      gimple stmt = gsi_stmt (gsi);
>>>> +
>>>> +      if (gimple_code (stmt) == GIMPLE_LABEL)
>>>> +       {
>>>> +         tree t = gimple_label_label (stmt);
>>>> +         gcc_assert (TREE_CODE (t) == LABEL_DECL);
>>>> +
>>>> +         m_label_bb_map.put (t, bb->bb->index);
>>>> +       }
>>>> +    }
>>>> +}
>>>> +
>>>> +/* Basic block equivalence comparison function that returns true if
>>>> +   basic blocks BB1 and BB2 (from functions FUNC1 and FUNC2) correspond.
>>>> +
>>>> +   In general, a collection of equivalence dictionaries is built for
>>>> types
>>>> +   like SSA names, declarations (VAR_DECL, PARM_DECL, ..). This
>>>> infrastructure
>>>> +   is utilized by every statement-by-stament comparison function.  */
>>>> +
>>>> +bool
>>>> +func_checker::compare_bb (sem_bb *bb1, sem_bb *bb2)
>>>> +{
>>>> +  unsigned i;
>>>> +  gimple_stmt_iterator gsi1, gsi2;
>>>> +  gimple s1, s2;
>>>> +
>>>> +  if (bb1->nondbg_stmt_count != bb2->nondbg_stmt_count
>>>> +      || bb1->edge_count != bb2->edge_count)
>>>> +    return return_false ();
>>>> +
>>>> +  gsi1 = gsi_start_bb (bb1->bb);
>>>> +  gsi2 = gsi_start_bb (bb2->bb);
>>>> +
>>>> +  for (i = 0; i < bb1->nondbg_stmt_count; i++)
>>>> +    {
>>>> +      if (is_gimple_debug (gsi_stmt (gsi1)))
>>>> +       gsi_next_nondebug (&gsi1);
>>>> +
>>>> +      if (is_gimple_debug (gsi_stmt (gsi2)))
>>>> +       gsi_next_nondebug (&gsi2);
>>>> +
>>>> +      s1 = gsi_stmt (gsi1);
>>>> +      s2 = gsi_stmt (gsi2);
>>>> +
>>>> +      int eh1 = lookup_stmt_eh_lp_fn
>>>> +               (DECL_STRUCT_FUNCTION (m_source_func_decl), s1);
>>>> +      int eh2 = lookup_stmt_eh_lp_fn
>>>> +               (DECL_STRUCT_FUNCTION (m_target_func_decl), s2);
>>>> +
>>>> +      if (eh1 != eh2)
>>>> +       return return_false_with_msg ("EH regions are different");
>>>> +
>>>> +      if (gimple_code (s1) != gimple_code (s2))
>>>> +       return return_false_with_msg ("gimple codes are different");
>>>> +
>>>> +      switch (gimple_code (s1))
>>>> +       {
>>>> +       case GIMPLE_CALL:
>>>> +         if (!compare_gimple_call (s1, s2))
>>>> +           return return_different_stmts (s1, s2, "GIMPLE_CALL");
>>>> +         break;
>>>> +       case GIMPLE_ASSIGN:
>>>> +         if (!compare_gimple_assign (s1, s2))
>>>> +           return return_different_stmts (s1, s2, "GIMPLE_ASSIGN");
>>>> +         break;
>>>> +       case GIMPLE_COND:
>>>> +         if (!compare_gimple_cond (s1, s2))
>>>> +           return return_different_stmts (s1, s2, "GIMPLE_COND");
>>>> +         break;
>>>> +       case GIMPLE_SWITCH:
>>>> +         if (!compare_gimple_switch (s1, s2))
>>>> +           return return_different_stmts (s1, s2, "GIMPLE_SWITCH");
>>>> +         break;
>>>> +       case GIMPLE_DEBUG:
>>>> +       case GIMPLE_EH_DISPATCH:
>>>> +         break;
>>>> +       case GIMPLE_RESX:
>>>> +         if (!compare_gimple_resx (s1, s2))
>>>> +           return return_different_stmts (s1, s2, "GIMPLE_RESX");
>>>> +         break;
>>>> +       case GIMPLE_LABEL:
>>>> +         if (!compare_gimple_label (s1, s2))
>>>> +           return return_different_stmts (s1, s2, "GIMPLE_LABEL");
>>>> +         break;
>>>> +       case GIMPLE_RETURN:
>>>> +         if (!compare_gimple_return (s1, s2))
>>>> +           return return_different_stmts (s1, s2, "GIMPLE_RETURN");
>>>> +         break;
>>>> +       case GIMPLE_GOTO:
>>>> +         if (!compare_gimple_goto (s1, s2))
>>>> +           return return_different_stmts (s1, s2, "GIMPLE_GOTO");
>>>> +         break;
>>>> +       case GIMPLE_ASM:
>>>> +         if (!compare_gimple_asm (s1, s2))
>>>> +           return return_different_stmts (s1, s2, "GIMPLE_ASM");
>>>> +         break;
>>>> +       case GIMPLE_PREDICT:
>>>> +       case GIMPLE_NOP:
>>>> +         return true;
>>>> +       default:
>>>> +         return return_false_with_msg ("Unknown GIMPLE code reached");
>>>> +       }
>>>> +
>>>> +      gsi_next (&gsi1);
>>>> +      gsi_next (&gsi2);
>>>> +    }
>>>> +
>>>> +  return true;
>>>> +}
>>>> +
>>>> +/* Verifies for given GIMPLEs S1 and S2 that
>>>> +   call statements are semantically equivalent.  */
>>>> +
>>>> +bool
>>>> +func_checker::compare_gimple_call (gimple s1, gimple s2)
>>>> +{
>>>> +  unsigned i;
>>>> +  tree t1, t2;
>>>> +
>>>> +  if (gimple_call_num_args (s1) != gimple_call_num_args (s2))
>>>> +    return false;
>>>> +
>>>> +  t1 = gimple_call_fndecl (s1);
>>>> +  t2 = gimple_call_fndecl (s2);
>>>> +
>>>> +  /* Function pointer variables are not supported yet.  */
>>>> +  if (t1 == NULL || t2 == NULL)
>>>> +    {
>>>> +      if (!compare_operand (t1, t2))
>>>> +       return return_false();
>>>
>>>
>>> I think the comment above is out of date. compare_operand should do the
>>> right
>>> job for indirect calls.
>>>>
>>>> +
>>>> +  if (cn1 && cn2 && cn1->weakref && cn2->weakref
>>>> +      && cn1->alias_target == cn2->alias_target)
>>>> +    return true;
>>>
>>>
>>> Lets consistently drop the weakrefs handling and add full alias handling
>>> incrementally.
>>>>
>>>> +
>>>> +  /* Checking function arguments.  */
>>>
>>> attributes
>>>>
>>>> +  tree decl1 = DECL_ATTRIBUTES (decl);
>>>> +  tree decl2 = DECL_ATTRIBUTES (m_compared_func->decl);
>>>
>>>
>>> You can still do this as part of the wap_comparison, right?
>>>>
>>>> +
>>>> +  m_checker = new func_checker (decl, m_compared_func->decl,
>>>> +                               compare_polymorphic_p (),
>>>> +                               false,
>>>> +                               &refs_set,
>>>> +                               &m_compared_func->refs_set);
>>>> +  while (decl1)
>>>> +    {
>>>> +      if (decl2 == NULL)
>>>> +       return return_false ();
>>>> +
>>>> +      if (get_attribute_name (decl1) != get_attribute_name (decl2))
>>>> +       return return_false ();
>>>> +
>>>> +      tree attr_value1 = TREE_VALUE (decl1);
>>>> +      tree attr_value2 = TREE_VALUE (decl2);
>>>> +
>>>> +      if (attr_value1 && attr_value2)
>>>> +       {
>>>> +         bool ret = m_checker->compare_operand (TREE_VALUE
>>>> (attr_value1),
>>>> +                                                TREE_VALUE
>>>> (attr_value2));
>>>> +         if (!ret)
>>>> +           return return_false_with_msg ("attribute values are
>>>> different");
>>>> +       }
>>>> +      else if (!attr_value1 && !attr_value2)
>>>> +       {}
>>>> +      else
>>>> +       return return_false ();
>>>> +
>>>> +      decl1 = TREE_CHAIN (decl1);
>>>> +      decl2 = TREE_CHAIN (decl2);
>>>> +    }
>>>> +
>>>> +  if (decl1 != decl2)
>>>> +    return return_false();
>>>> +
>>>> +
>>>> +  for (arg1 = DECL_ARGUMENTS (decl),
>>>> +       arg2 = DECL_ARGUMENTS (m_compared_func->decl);
>>>> +       arg1; arg1 = DECL_CHAIN (arg1), arg2 = DECL_CHAIN (arg2))
>>>> +    if (!m_checker->compare_decl (arg1, arg2))
>>>> +      return return_false ();
>>>> +
>>>> +  /* Fill-up label dictionary.  */
>>>> +  for (unsigned i = 0; i < bb_sorted.length (); ++i)
>>>> +    {
>>>> +      m_checker->parse_labels (bb_sorted[i]);
>>>> +      m_checker->parse_labels (m_compared_func->bb_sorted[i]);
>>>> +    }
>>>> +
>>>> +  /* Checking all basic blocks.  */
>>>> +  for (unsigned i = 0; i < bb_sorted.length (); ++i)
>>>> +    if(!m_checker->compare_bb (bb_sorted[i],
>>>> m_compared_func->bb_sorted[i]))
>>>> +      return return_false();
>>>> +
>>>> +  dump_message ("All BBs are equal\n");
>>>> +
>>>> +  /* Basic block edges check.  */
>>>> +  for (unsigned i = 0; i < bb_sorted.length (); ++i)
>>>> +    {
>>>> +      bb_dict = XNEWVEC (int, bb_sorted.length () + 2);
>>>> +      memset (bb_dict, -1, (bb_sorted.length () + 2) * sizeof (int));
>>>> +
>>>> +      bb1 = bb_sorted[i]->bb;
>>>> +      bb2 = m_compared_func->bb_sorted[i]->bb;
>>>> +
>>>> +      ei2 = ei_start (bb2->preds);
>>>> +
>>>> +      for (ei1 = ei_start (bb1->preds); ei_cond (ei1, &e1); ei_next
>>>> (&ei1))
>>>> +       {
>>>> +         ei_cond (ei2, &e2);
>>>> +
>>>> +         if (e1->flags != e2->flags)
>>>> +           return return_false_with_msg ("flags comparison returns
>>>> false");
>>>> +
>>>> +         if (!bb_dict_test (bb_dict, e1->src->index, e2->src->index))
>>>> +           return return_false_with_msg ("edge comparison returns
>>>> false");
>>>> +
>>>> +         if (!bb_dict_test (bb_dict, e1->dest->index, e2->dest->index))
>>>> +           return return_false_with_msg ("BB comparison returns false");
>>>> +
>>>> +         if (!m_checker->compare_edge (e1, e2))
>>>> +           return return_false_with_msg ("edge comparison returns
>>>> false");
>>>> +
>>>> +         ei_next (&ei2);
>>>> +       }
>>>> +    }
>>>> +
>>>> +  /* Basic block PHI nodes comparison.  */
>>>> +  for (unsigned i = 0; i < bb_sorted.length (); i++)
>>>> +    if (!compare_phi_node (bb_sorted[i]->bb,
>>>> m_compared_func->bb_sorted[i]->bb))
>>>> +      return return_false_with_msg ("PHI node comparison returns
>>>> false");
>>>> +
>>>> +  return result;
>>>> +}
>>>
>>>
>>> The rest of patch seems fine.  I think we went across enough of
>>> iteraitons, the patch is OK
>>> with changes above and lets handle rest incrementally.
>>>
>>> Thanks!
>>> Honza
>>>
>>
>> Hello
>>
>> There's final version of the patch I'm going to commit tomorrow in the
>> morning (CEST).
>> Thank you Honza for the review.
>>
>> Martin