Re: [RFC][IPA-VRP] Early VRP Implementation

[Richard Biener <richard dot guenther at gmail dot com>]

On Tue, Aug 23, 2016 at 4:11 AM, Kugan Vivekanandarajah
<kugan.vivekanandarajah@linaro.org> wrote:
> Hi,
>
> On 19 August 2016 at 21:41, Richard Biener <richard.guenther@gmail.com> wrote:
>> On Tue, Aug 16, 2016 at 9:45 AM, kugan
>> <kugan.vivekanandarajah@linaro.org> wrote:
>>> Hi Richard,
>>>
>>> On 12/08/16 20:43, Richard Biener wrote:
>>>>
>>>> On Wed, Aug 3, 2016 at 3:17 AM, kugan <kugan.vivekanandarajah@linaro.org>
>>>> wrote:
>>>
>>>
>>> [SNIP]
>>>
>>>>
>>>> diff --git a/gcc/common.opt b/gcc/common.opt
>>>> index 8a292ed..7028cd4 100644
>>>> --- a/gcc/common.opt
>>>> +++ b/gcc/common.opt
>>>> @@ -2482,6 +2482,10 @@ ftree-vrp
>>>>  Common Report Var(flag_tree_vrp) Init(0) Optimization
>>>>  Perform Value Range Propagation on trees.
>>>>
>>>> +fdisable-tree-evrp
>>>> +Common Report Var(flag_disable_early_vrp) Init(0) Optimization
>>>> +Disable Early Value Range Propagation on trees.
>>>> +
>>>>
>>>> no please, this is automatically supported via -fdisable-
>>>
>>>
>>> I am now having -ftree-evrp which is enabled all the time. But This will
>>> only be used for disabling the early-vrp. That is, early-vrp will be run
>>> when ftree-vrp is enabled and ftree-evrp is not explicitly disabled. Is this
>>> OK?
>>
>> Why would one want to disable early-vrp?  I see you do this in the testsuite
>> for non-early VRP unit-tests but using -fdisable-tree-evrp1 there
>> would be ok as well.
>
> Removed it altogether. I though that you wanted a way to disable
> early-vrp for testing purposes.

But there is via the generic -fdisable-tree-DUMPFILE way.

>>>>
>>>> @@ -1728,11 +1736,12 @@ extract_range_from_assert (value_range *vr_p, tree
>>>> expr)
>>>>      always false.  */
>>>>
>>>>  static void
>>>> -extract_range_from_ssa_name (value_range *vr, tree var)
>>>> +extract_range_from_ssa_name (value_range *vr, bool dom_p, tree var)
>>>>  {
>>>>    value_range *var_vr = get_value_range (var);
>>>>
>>>> -  if (var_vr->type != VR_VARYING)
>>>> +  if (var_vr->type != VR_VARYING
>>>> +      && (!dom_p || var_vr->type != VR_UNDEFINED))
>>>>      copy_value_range (vr, var_vr);
>>>>    else
>>>>      set_value_range (vr, VR_RANGE, var, var, NULL);
>>>>
>>>> why do you need these changes?  I think I already told you you need to
>>>> initialize the lattice to sth else than VR_UNDEFINED and that you can't
>>>> fully re-use update_value_range.  If you don't want to do that then
>>>> instead
>>>> of doing changes all over the place do it in get_value_range and have a
>>>> global flag.
>>>
>>>
>>> I have now added a global early_vrp_p and use this to initialize
>>> VR_INITIALIZER and get_value_range default to VR_VARYING.
>>
>> ICK.  Ok, I see that this works, but it is quite ugly, so (see below)
>>
>>>>
>>>>
>>>> @@ -3594,7 +3643,8 @@ extract_range_from_cond_expr (value_range *vr,
>>>> gassign *stmt)
>>>>     on the range of its operand and the expression code.  */
>>>>
>>>>  static void
>>>> -extract_range_from_comparison (value_range *vr, enum tree_code code,
>>>> +extract_range_from_comparison (value_range *vr,
>>>> +                              enum tree_code code,
>>>>                                tree type, tree op0, tree op1)
>>>>  {
>>>>    bool sop = false;
>>>>
>>>> remove these kind of no-op changes.
>>>
>>>
>>> Done.
>>>
>>>
>>>>
>>>> +/* Initialize local data structures for VRP.  If DOM_P is true,
>>>> +   we will be calling this from early_vrp where value range propagation
>>>> +   is done by visiting stmts in dominator tree.  ssa_propagate engine
>>>> +   is not used in this case and that part of the ininitialization will
>>>> +   be skipped.  */
>>>>
>>>>  static void
>>>> -vrp_initialize (void)
>>>> +vrp_initialize (bool dom_p)
>>>>  {
>>>>    basic_block bb;
>>>>
>>>> @@ -6949,6 +7010,9 @@ vrp_initialize (void)
>>>>    vr_phi_edge_counts = XCNEWVEC (int, num_ssa_names);
>>>>    bitmap_obstack_initialize (&vrp_equiv_obstack);
>>>>
>>>> +  if (dom_p)
>>>> +    return;
>>>> +
>>>>
>>>> split the function instead.
>>>>
>>>> @@ -7926,7 +7992,8 @@ vrp_visit_switch_stmt (gswitch *stmt, edge
>>>> *taken_edge_p)
>>>>     If STMT produces a varying value, return SSA_PROP_VARYING.  */
>>>>
>>>>  static enum ssa_prop_result
>>>> -vrp_visit_stmt (gimple *stmt, edge *taken_edge_p, tree *output_p)
>>>> +vrp_visit_stmt_worker (gimple *stmt, bool dom_p,  edge *taken_edge_p,
>>>> +                      tree *output_p)
>>>>  {
>>>>    tree def;
>>>>    ssa_op_iter iter;
>>>> @@ -7940,7 +8007,7 @@ vrp_visit_stmt (gimple *stmt, edge
>>>> *taken_edge_p, tree *output_p)
>>>>    if (!stmt_interesting_for_vrp (stmt))
>>>>      gcc_assert (stmt_ends_bb_p (stmt));
>>>>    else if (is_gimple_assign (stmt) || is_gimple_call (stmt))
>>>> -    return vrp_visit_assignment_or_call (stmt, output_p);
>>>> +    return vrp_visit_assignment_or_call (stmt, dom_p, output_p);
>>>>    else if (gimple_code (stmt) == GIMPLE_COND)
>>>>      return vrp_visit_cond_stmt (as_a <gcond *> (stmt), taken_edge_p);
>>>>    else if (gimple_code (stmt) == GIMPLE_SWITCH)
>>>> @@ -7954,6 +8021,12 @@ vrp_visit_stmt (gimple *stmt, edge
>>>> *taken_edge_p, tree *output_p)
>>>>    return SSA_PROP_VARYING;
>>>>  }
>>>>
>>>> +static enum ssa_prop_result
>>>> +vrp_visit_stmt (gimple *stmt, edge *taken_edge_p, tree *output_p)
>>>> +{
>>>> +  return vrp_visit_stmt_worker (stmt, false, taken_edge_p, output_p);
>>>> +}
>>>>
>>>> as said the refactoring that would be appreciated is to split out the
>>>> update_value_range calls
>>>> from the worker functions so you can call the respective functions
>>>> from the DOM implementations.
>>>> That they are globbed in vrp_visit_stmt currently is due to the API of
>>>> the SSA propagator.
>>>
>>> Sent this as separate patch for easy reviewing and testing.
>>
>> Thanks.
>>
>>>>
>>>> @@ -8768,6 +8842,12 @@ vrp_visit_phi_node (gphi *phi)
>>>>               fprintf (dump_file, "\n");
>>>>             }
>>>>
>>>> +         if (dom_p && vr_arg.type == VR_UNDEFINED)
>>>> +           {
>>>> +             set_value_range_to_varying (&vr_result);
>>>> +             break;
>>>> +           }
>>>> +
>>>>
>>>> eh...  ok, so another way to attack this is, instead of initializing
>>>> the lattice to sth else
>>>> than VR_UNDEFINED, make sure to drop the lattice to varying for all PHI
>>>> args on
>>>> yet unvisited incoming edges (you're not doing optimistic VRP).  That's
>>>> the only
>>>> place you _have_ to do it.
>>>
>>>
>>> Even when it is initialize (as I am doing now), we can still end up with
>>> VR_UNDEFINED during the propagation.  I have just left the above so that we
>>> dont end up with the wrong VR.
>>
>> How would we end up with wrong VRs?  I see
>>
>> +         /* Discover VR when condition is true.  */
>> +         extract_range_for_var_from_comparison_expr (op0, code, op0, op1, &vr);
>> +         if (old_vr->type == VR_RANGE || old_vr->type == VR_ANTI_RANGE)
>> +           vrp_intersect_ranges (&vr, old_vr);
>>
>> where you already disregard UNDEFINED as old_vr.
>>
>> What you might be missing is to set all DEFs on !stmt_interesting_for_vrp to
>> VARYING.  Also
>>
>> +      if (stmt_interesting_for_vrp (stmt))
>> +       {
>> +         tree lhs = gimple_get_lhs (stmt);
>> +         value_range vr = VR_INITIALIZER;
>> +         vrp_visit_stmt_worker (stmt, &taken_edge, &output, &vr);
>> +         update_value_range (lhs, &vr);
>> +
>> +         /* Try folding stmts with the VR discovered.  */
>> +         if (fold_stmt (&gsi, follow_single_use_edges))
>> +           update_stmt (gsi_stmt (gsi));
>>
>> folding here can introduce additional stmts and thus unvisited SSA defs
>> which would end up with VR_UNINITIALIZED defs - I don't see exactly
>> where that would cause issues but I'm not sure it might not.  So better
>> use fold_stmt_inplace or alternatively if fold_stmt returned true then,
>> remembering the previous stmt gsi, iterate over all stmts emitted and
>> set their defs to varying (or re-visit them).  See for example how
>> tree-ssa-forwprop.c does this re-visiting (it revisits all changed stmts).
>
> I am now setting the results of stmts that are not interesting to vrp
> to VR_VARYING.
>
> Also, before visiting PHI, if any of the arguments are undefined,
> result of the PHI is also set varying.
>
> I have removed all the others. This now bootstraps and passes
> regressions (see attached patch).
>
>
>> Note that you want to have a custom valueize function instead of just
>> follow_single_use_edges as you want to valueize all SSA names according
>> to their lattice value (if it has a single value).  You can use vrp_valueize
>> for this though that gets you non-single-use edge following as well.
>> Eventually it's going to be cleaner to do what the SSA propagator does and
>> before folding do
>>
>>    did_replace = replace_uses_in (stmt, vrp_valueize);
>>    if (fold_stmt (&gsi, follow_single_use_edges)
>>        || did_replace)
>>      update_stmt (gsi_stmt (gsi));
>>
>> exporting replace_uses_in for this is ok.  I guess I prefer this for now.
>
> I also added the above.  I noticed that I need
> recompute_tree_invariant_for_addr_expr as in ssa_propagate. My initial
> implementation also had gimple_purge_all_dead_eh_edges and
> fixup_noreturn_call as in ssa_propagat but I thinj that is not needed
> as it would be done at the end of the pass.

I don't see this being done at the end of the pass.  So please re-instantiate
that parts.

> With this I noticed more stmts are folded before vrp1. This required
> me to adjust some testcases.
>
>>
>> Overall this now looks good apart from the folding and the VR_INITIALIZER thing.
>>
>> You can commit the already approved refactoring changes and combine this
>> patch with the struct value_range move, this way I can more easily look into
>> issues with the UNDEFINED thing if you can come up with a testcase that
>> doesn't work.
>>
>
> I have now committed all the dependent patches.
>
> Attached patch passes regression and bootstrap except pr33738.C. This
> is an unrelated issue as discussed in
> https://gcc.gnu.org/ml/gcc-patches/2016-08/msg01386.html
>
> Is this OK?

+/* Initialize local data structures for VRP.  If DOM_P is true,
+   we will be calling this from early_vrp where value range propagation
+   is done by visiting stmts in dominator tree.  ssa_propagate engine
+   is not used in this case and that part of the ininitialization will
+   be skipped.  */
+
+static void
+vrp_initialize ()

comment needs updating now.


 static void
-extract_range_from_phi_node (gphi *phi, value_range *vr_result)
+extract_range_from_phi_node (gphi *phi, value_range *vr_result,
+                            bool early_vrp_p)
 {


I don't think you need this changes now that you have
stmt_visit_phi_node_in_dom_p
guarding its call.

+static bool
+stmt_visit_phi_node_in_dom_p (gphi *phi)
+{
+  ssa_op_iter iter;
+  use_operand_p oprnd;
+  tree op;
+  value_range *vr;
+  FOR_EACH_PHI_ARG (oprnd, phi, iter, SSA_OP_USE)
+    {
+      op = USE_FROM_PTR (oprnd);
+      if (TREE_CODE (op) == SSA_NAME)
+       {
+         vr = get_value_range (op);
+         if (vr->type == VR_UNDEFINED)
+           return false;
+       }
+    }

I think this is overly conservative in never allowing UNDEFINED on PHI
node args (even if the def was actually visited).  I think that the most
easy way to improve this bit would be to actually track visited blocks.
You already set the EDGE_EXECUTABLE flag on edges so you could
clear BB_VISITED on all blocks and set it in the before_dom_children
hook (at the end).  Then the above can be folded into the PHI visiting:

    bool has_unvisited_pred = false;
    FOR_EACH_EDGE (e, ei, bb->preds)
       if (!(e->src->flags & BB_VISITED))
         {
            has_unvisited_preds = true;
            break;
         }

+  /* Visit PHI stmts and discover any new VRs possible.  */
+  gimple_stmt_iterator gsi;
+  for (gphi_iterator gpi = gsi_start_phis (bb);
+       !gsi_end_p (gpi); gsi_next (&gpi))
+    {
+      gphi *phi = gpi.phi ();
+      tree lhs = PHI_RESULT (phi);
+      value_range vr_result = VR_INITIALIZER;
+      if (! has_unvisived_preds
           && stmt_interesting_for_vrp (phi)
+         && stmt_visit_phi_node_in_dom_p (phi))
+       extract_range_from_phi_node (phi, &vr_result, true);
+      else
+       set_value_range_to_varying (&vr_result);
+      update_value_range (lhs, &vr_result);
+    }

due to a bug in IRA you need to make sure to un-set BB_VISITED after
early-vrp is finished again.

+         /* Try folding stmts with the VR discovered.  */
+         bool did_replace = replace_uses_in (stmt, evrp_valueize);
+         if (fold_stmt (&gsi, follow_single_use_edges)
+             || did_replace)
+           update_stmt (gsi_stmt (gsi));

you should be able to re-use vrp_valueize here.

+         def_operand_p def_p = SINGLE_SSA_DEF_OPERAND (stmt, SSA_OP_DEF);
+         /* Set the SSA with the value range.  */
+         if (def_p
+             && TREE_CODE (DEF_FROM_PTR (def_p)) == SSA_NAME
+             && INTEGRAL_TYPE_P (TREE_TYPE (DEF_FROM_PTR (def_p))))
+           {
+             tree def = DEF_FROM_PTR (def_p);
+             unsigned ver = SSA_NAME_VERSION (def);
+             if ((vr_value[ver]->type == VR_RANGE

Use get_value_range () please, not direct access to vr_value.

+                  || vr_value[ver]->type == VR_ANTI_RANGE)
+                 && (TREE_CODE (vr_value[ver]->min) == INTEGER_CST)
+                 && (TREE_CODE (vr_value[ver]->max) == INTEGER_CST))
+               set_range_info (def, vr_value[ver]->type, vr_value[ver]->min,
+                               vr_value[ver]->max);
+           }

Otherwise the patch looks good now (with a lot of improvement
possibilities of course).

Thanks and sorry for the delay,
Richard.

> Thanks,
> Kugan
>
>
>> Thanks,
>> Richard.
>>
>>> I also noticed that g++.dg/warn/pr33738.C testcase is now failing. This is
>>> because, with early-vrp setting value range ccp2 is optimizing without
>>> issuing a warning. I will look into it.
>>>
>>> bootstrap and regression testing is in progress.
>>>
>>> Thanks,
>>> Kugan