Re: [PATCH,1/2] Extended if-conversion for loops marked with pragma omp simd.

[Yuri Rumyantsev <ysrumyan at gmail dot com>]

Richard,

Thanks for your answer!

In current implementation phi node conversion assume that one of
incoming edge to bb containing given phi has at least one non-critical
edge and choose it to insert predicated code. But if we choose
critical edge we need to determine insert point and insertion
direction (before/after) since in other case we can get invalid ssa
form (use before def). This is done by my new function which is not in
current patch ( I will present this patch later). SO I assume that we
need to leave this patch as it is to not introduce new bugs.

Thanks.
Yuri.

2014-10-20 12:00 GMT+04:00 Richard Biener <richard.guenther@gmail.com>:
> On Fri, Oct 17, 2014 at 4:09 PM, Yuri Rumyantsev <ysrumyan@gmail.com> wrote:
>> Richard,
>>
>> I reworked the patch as you proposed, but I didn't understand what
>> did you mean by:
>>
>>>So please rework the patch so critical edges are always handled
>>>correctly.
>>
>> In current patch flag_force_vectorize is used (1) to reject phi nodes
>> with more than 2 arguments; (2) to reject basic blocks with only
>> critical incoming edges since support for extended predication of phi
>> nodes will be in next patch.
>
> I mean that (2) should not be rejected dependent on flag_force_vectorize.
> It was rejected because if-cvt couldn't handle it correctly before but with
> this patch this is fixed.  I see no reason to still reject this then even
> for !flag_force_vectorize.
>
> Rejecting PHIs with more than two arguments with flag_force_vectorize
> is ok.
>
> Richard.
>
>> Could you please clarify your statement.
>>
>> I attached modified patch.
>>
>> ChangeLog:
>>
>> 2014-10-17  Yuri Rumyantsev  <ysrumyan@gmail.com>
>>
>> (flag_force_vectorize): New variable.
>> (edge_predicate): New function.
>> (set_edge_predicate): New function.
>> (add_to_dst_predicate_list): Conditionally invoke add_to_predicate_list
>> if destination block of edge is not always executed. Set-up predicate
>> for critical edge.
>> (if_convertible_phi_p): Accept phi nodes with more than two args
>> if FLAG_FORCE_VECTORIZE was set-up.
>> (ifcvt_can_use_mask_load_store): Use FLAG_FORCE_VECTORIZE.
>> (if_convertible_stmt_p): Fix up pre-function comments.
>> (all_edges_are_critical): New function.
>> (if_convertible_bb_p): Use call of all_preds_critical_p
>> to reject block if-conversion with incoming critical edges only if
>> FLAG_FORCE_VECTORIZE was not set-up.
>> (predicate_bbs): Skip loop exit block also.Invoke build2_loc
>> to compute predicate instead of fold_build2_loc.
>> Add zeroing of edge 'aux' field.
>> (find_phi_replacement_condition): Extend function interface:
>> it returns NULL if given phi node must be handled by means of
>> extended phi node predication. If number of predecessors of phi-block
>> is equal 2 and atleast one incoming edge is not critical original
>> algorithm is used.
>> (tree_if_conversion): Temporary set-up FLAG_FORCE_VECTORIZE to false.
>> Nullify 'aux' field of edges for blocks with two successors.
>>
>>
>>
>>
>> 2014-10-17 13:09 GMT+04:00 Richard Biener <richard.guenther@gmail.com>:
>>> On Thu, Oct 16, 2014 at 5:42 PM, Yuri Rumyantsev <ysrumyan@gmail.com> wrote:
>>>> Richard,
>>>>
>>>> Here is reduced patch as you requested. All your remarks have been fixed.
>>>> Could you please look at it ( I have already sent the patch with
>>>> changes in add_to_predicate_list for review).
>>>
>>> +             if (dump_file && (dump_flags & TDF_DETAILS))
>>> +               fprintf (dump_file, "More than two phi node args.\n");
>>> +             return false;
>>> +           }
>>> +
>>> +        }
>>>
>>> Excess vertical space.
>>>
>>>
>>> +/* Assumes that BB has more than 2 predecessors.
>>>
>>> More than 1 predecessor?
>>>
>>> +   Returns false if at least one successor is not on critical edge
>>> +   and true otherwise.  */
>>> +
>>> +static inline bool
>>> +all_edges_are_critical (basic_block bb)
>>> +{
>>>
>>> "all_preds_critical_p" would be a better name
>>>
>>> +  if (EDGE_COUNT (bb->preds) > 2)
>>> +    {
>>> +      if (!flag_force_vectorize)
>>> +       return false;
>>> +    }
>>>
>>> as I said in the last review I don't think we should restrict edge
>>> predicates to flag_force_vectorize.  At least I can't see how
>>> if-conversion is magically more expensive for that case?
>>>
>>> So please rework the patch so critical edges are always handled
>>> correctly.
>>>
>>> Ok with that and the above suggested changes.
>>>
>>> Thanks,
>>> Richard.
>>>
>>>
>>>> Thanks.
>>>> Yuri.
>>>> ChangeLog
>>>> 2014-10-16  Yuri Rumyantsev  <ysrumyan@gmail.com>
>>>>
>>>> (flag_force_vectorize): New variable.
>>>> (edge_predicate): New function.
>>>> (set_edge_predicate): New function.
>>>> (add_to_dst_predicate_list): Conditionally invoke add_to_predicate_list
>>>> if destination block of edge is not always executed. Set-up predicate
>>>> for critical edge.
>>>> (if_convertible_phi_p): Accept phi nodes with more than two args
>>>> if FLAG_FORCE_VECTORIZE was set-up.
>>>> (ifcvt_can_use_mask_load_store): Use FLAG_FORCE_VECTORIZE.
>>>> (if_convertible_stmt_p): Fix up pre-function comments.
>>>> (all_edges_are_critical): New function.
>>>> (if_convertible_bb_p): Allow bb has more than two predecessors if
>>>> FLAG_FORCE_VECTORIZE was set-up. Use call of all_edges_are_critical
>>>> to reject block if-conversion with incoming critical edges only if
>>>> FLAG_FORCE_VECTORIZE was not set-up.
>>>> (predicate_bbs): Skip loop exit block also.Invoke build2_loc
>>>> to compute predicate instead of fold_build2_loc.
>>>> Add zeroing of edge 'aux' field.
>>>> (find_phi_replacement_condition): Extend function interface:
>>>> it returns NULL if given phi node must be handled by means of
>>>> extended phi node predication. If number of predecessors of phi-block
>>>> is equal 2 and atleast one incoming edge is not critical original
>>>> algorithm is used.
>>>> (tree_if_conversion): Temporary set-up FLAG_FORCE_VECTORIZE to false.
>>>> Nullify 'aux' field of edges for blocks with two successors.
>>>>
>>>>
>>>>
>>>> 2014-10-15 13:50 GMT+04:00 Richard Biener <richard.guenther@gmail.com>:
>>>>> On Mon, Oct 13, 2014 at 11:38 AM, Yuri Rumyantsev <ysrumyan@gmail.com> wrote:
>>>>>> Richard,
>>>>>>
>>>>>> Here is updated patch (part1) for extended if conversion.
>>>>>>
>>>>>> Second part of patch will be sent later.
>>>>>
>>>>> Ok, I'm starting to look at this.  I'd still like you to split things up
>>>>> more.
>>>>>
>>>>>  static inline void
>>>>>  add_to_predicate_list (struct loop *loop, basic_block bb, tree nc)
>>>>>  {
>>>>> ...
>>>>>
>>>>> +      /* We use notion of cd equivalence to get simplier predicate for
>>>>> +        join block, e.g. if join block has 2 predecessors with predicates
>>>>> +        p1 & p2 and p1 & !p2, we'd like to get p1 for it instead of
>>>>> +        p1 & p2 | p1 & !p2.  */
>>>>> +      if (dom_bb != loop->header
>>>>> +         && get_immediate_dominator (CDI_POST_DOMINATORS, dom_bb) == bb)
>>>>> +       {
>>>>> +         gcc_assert (flow_bb_inside_loop_p (loop, dom_bb));
>>>>> +         bc = bb_predicate (dom_bb);
>>>>> +         gcc_assert (!is_true_predicate (bc));
>>>>>
>>>>> these changes look worthwhile even for !flag_force_vectorize.  So please
>>>>> split the change to add_to_predicate_list out and compute post-dominators
>>>>> unconditionally.  Note that you should call free_dominance_info
>>>>> (CDI_POST_DOMINATORS) at the end of if-conversion.
>>>>>
>>>>> +  if (!dominated_by_p (CDI_DOMINATORS, loop->latch, e->dest))
>>>>> +    add_to_predicate_list (loop, e->dest, cond);
>>>>> +
>>>>> +  /* If edge E is critical save predicate on it.  */
>>>>> +  if (EDGE_COUNT (e->dest->preds) >= 2)
>>>>> +    set_edge_predicate (e, cond);
>>>>>
>>>>> how do we know the edge is critical by this simple check?  Why not
>>>>> simply always save edge predicates (well, you kind of do but omit
>>>>> the case where e->src dominates e->dest).
>>>>>
>>>>> Btw, you can rely on edge->aux being NULL at the start of the
>>>>> pass but need to clear it at the end (best use clear_aux_for_edges ()
>>>>> for that).  So stuff like
>>>>>
>>>>> +         extract_true_false_edges_from_block (bb, &true_edge, &false_edge);
>>>>> +         if (flag_force_vectorize)
>>>>> +           true_edge->aux = false_edge->aux = NULL;
>>>>>
>>>>> shouldn't be necessary.
>>>>>
>>>>> I think the edge predicate handling should also be unconditionally
>>>>> and not depend on flag_force_vectorize.
>>>>>
>>>>> +      /* The loop latch and loop exit block are always executed and
>>>>> +        have no extra conditions to be processed: skip them.  */
>>>>> +      if (bb == loop->latch
>>>>> +         || bb_with_exit_edge_p (loop, bb))
>>>>>
>>>>> I don't think the edge stuff is true - given you still only reset the
>>>>> loop->latch bb predicate the change looks broken.
>>>>>
>>>>> +         /* Fold_build2 can produce bool conversion which is not
>>>>> +             supported by vectorizer, so re-build it without folding.
>>>>> +            For example, such conversion is generated for sequence:
>>>>> +               _Bool _7, _8, _9;
>>>>> +               _7 = _6 != 13; _8 = _6 != 0; _9 = _8 & _9;
>>>>> +               if (_9 != 0)  --> (bool)_9.  */
>>>>> +
>>>>> +         if (CONVERT_EXPR_P (c)
>>>>> +             && TREE_CODE_CLASS (code) == tcc_comparison)
>>>>>
>>>>> I think you should simply use canonicalize_cond_expr_cond on the
>>>>> folding result.  Or rather _not_ fold at all - we are taking the
>>>>> operands from the GIMPLE condition unmodified after all.
>>>>>
>>>>> -         add_to_dst_predicate_list (loop, false_edge,
>>>>> -                                    unshare_expr (cond), c2);
>>>>> +         add_to_dst_predicate_list (loop, false_edge, unshare_expr (cond),
>>>>> +                                    unshare_expr (c2));
>>>>>
>>>>> why is it necessary to unshare c2?
>>>>>
>>>>> Please split out the PHI-with-multi-arg handling  (I have not looked at
>>>>> that in detail).
>>>>>
>>>>> Thanks,
>>>>> Richard.
>>>>>
>>>>>
>>>>>> Changelog.
>>>>>>
>>>>>> 2014-10-13  Yuri Rumyantsev  <ysrumyan@gmail.com>
>>>>>>
>>>>>> * tree-if-conv.c (cgraph.h): Add include file to detect function clone.
>>>>>> (flag_force_vectorize): New variable.
>>>>>> (edge_predicate): New function.
>>>>>> (set_edge_predicate): New function.
>>>>>> (add_to_predicate_list): Check unconditionally that bb is always
>>>>>> executed to early exit. Use predicate of cd-equivalent block
>>>>>> for join blocks if it exists.
>>>>>> (add_to_dst_predicate_list): Invoke add_to_predicate_list if
>>>>>> destination block of edge is not always executed. Set-up predicate
>>>>>> for critical edge.
>>>>>> (if_convertible_phi_p): Accept phi nodes with more than two args
>>>>>> if FLAG_FORCE_VECTORIZE was set-up.
>>>>>> (ifcvt_can_use_mask_load_store): Use FLAG_FORCE_VECTORIZE.
>>>>>> (if_convertible_stmt_p): Fix up pre-function comments.
>>>>>> (all_edges_are_critical): New function.
>>>>>> (if_convertible_bb_p): Allow bb has more than two predecessors if
>>>>>> FLAG_FORCE_VECTORIZE was set-up. Use call of all_edges_are_critical
>>>>>> to reject block if-conversion with incoming critical edges only if
>>>>>> FLAG_FORCE_VECTORIZE was not set-up.
>>>>>> (predicate_bbs): Skip loop exit block also. Add check that if
>>>>>> fold_build2 produces bool conversion, recompute predicate using
>>>>>> build2_loc. Add zeroing of edge 'aux' field under FLAG_FORCE_VECTORIZE.
>>>>>> (if_convertible_loop_p_1): Recompute POST_DOMINATOR tree if
>>>>>> FLAG_FORCE_VECTORIZE was set-up to calculate cd equivalent bb's.
>>>>>> (find_phi_replacement_condition): Extend function interface:
>>>>>> it returns NULL if given phi node must be handled by means of
>>>>>> extended phi node predication. If number of predecessors of phi-block
>>>>>> is equal 2 and atleast one incoming edge is not critical original
>>>>>> algorithm is used.
>>>>>> (get_predicate_for_edge): New function.
>>>>>> (find_insertion_point): New function.
>>>>>> (predicate_arbitrary_scalar_phi): New function.
>>>>>> (predicate_all_scalar_phis): Introduce new variable BEFORE.
>>>>>> Invoke find_insertion_point to initialize gsi and
>>>>>> predicate_arbitrary_scalar_phi if TRUE_BB is NULL - it signals
>>>>>> that extended predication must be applied).
>>>>>> (insert_gimplified_predicates): Add test for non-predicated basic
>>>>>> blocks that there are no gimplified statements to insert. Insert
>>>>>> predicates at the block begining for extended if-conversion.
>>>>>> (tree_if_conversion): Initialize flag_force_vectorize from current
>>>>>> loop or outer loop (to support pragma omp declare).Do loop versioning
>>>>>> for innermost loop marked with pragma omp simd and
>>>>>> FLAG_TREE_LOOP_IF_CONVERT was not sett-up. Nullify 'aux' field of edges
>>>>>> for blocks with two successors.
>>>>>>
>>>>>>
>>>>>>
>>>>>>
>>>>>> 2014-09-22 12:28 GMT+04:00 Yuri Rumyantsev <ysrumyan@gmail.com>:
>>>>>>> Richard,
>>>>>>>
>>>>>>> here is reduced patch (part.1) which was reduced almost twice.
>>>>>>> Let's me also answer on your comments.
>>>>>>>
>>>>>>> 1. I really use edge field 'aux' to keep predicate for critical edges.
>>>>>>> My previous code was not correct and now it looks like:
>>>>>>>
>>>>>>>   if (EDGE_COUNT (b->succs) == 1 || EDGE_COUNT (e->dest->preds) == 1)
>>>>>>>     /* Edge E is not critical,  use predicate of edge source bb. */
>>>>>>>     c = bb_predicate (b);
>>>>>>>   else
>>>>>>>     /* Edge E is critical and its aux field contains predicate.  */
>>>>>>>     c = edge_predicate (e);
>>>>>>>
>>>>>>> 2. I completely delete all code related to creation of conditional
>>>>>>> expressions and completely rely on bool pattern recognition in
>>>>>>> vectorizer. But we need to delete all dead predicate computations
>>>>>>> which are not used since they prevent vectorization. I will add this
>>>>>>> local-dce function in next patch.
>>>>>>> 3. I also did not include in this patch recognition of general
>>>>>>> phi-nodes with two arguments only for which conversion of conditional
>>>>>>> scalar reduction can be applied also.
>>>>>>> Note that all these changes are applied for loop marked with pragma
>>>>>>> omp simd only.
>>>>>>>
>>>>>>> 2014-09-22  Yuri Rumyantsev  <ysrumyan@gmail.com>
>>>>>>>
>>>>>>> * tree-if-conv.c (cgraph.h): Add include file to detect function clone.
>>>>>>> (flag_force_vectorize): New variable.
>>>>>>> (edge_predicate): New function.
>>>>>>> (set_edge_predicate): New function.
>>>>>>> (convert_name_to_cmp): New function.
>>>>>>> (add_to_predicate_list): Check unconditionally that bb is always
>>>>>>> executed to early exit. Use predicate of cd-equivalent block
>>>>>>> for join blocks if it exists.
>>>>>>> (add_to_dst_predicate_list): Invoke add_to_predicate_list if
>>>>>>> destination block of edge is not always executed. Set-up predicate
>>>>>>> for critical edge.
>>>>>>> (if_convertible_phi_p): Accept phi nodes with more than two args
>>>>>>> if FLAG_FORCE_VECTORIZE was set-up.
>>>>>>> (ifcvt_can_use_mask_load_store): Use FLAG_FORCE_VECTORIZE.
>>>>>>> (if_convertible_stmt_p): Fix up pre-function comments.
>>>>>>> (all_edges_are_critical): New function.
>>>>>>> (if_convertible_bb_p): Allow bb has more than two predecessors if
>>>>>>> FLAG_FORCE_VECTORIZE was set-up. Use call of all_edges_are_critical
>>>>>>> to reject block if-conversion with incoming critical edges only if
>>>>>>> FLAG_FORCE_VECTORIZE was not set-up.
>>>>>>> (predicate_bbs): Skip loop exit block also. Add check that if
>>>>>>> fold_build2 produces bool conversion, recompute predicate using
>>>>>>> build2_loc. Add zeroing of edge 'aux' field under FLAG_FORCE_VECTORIZE.
>>>>>>> (if_convertible_loop_p_1): Recompute POST_DOMINATOR tree if
>>>>>>> FLAG_FORCE_VECTORIZE was set-up to calculate cd equivalent bb's.
>>>>>>> (find_phi_replacement_condition): Extend function interface:
>>>>>>> it returns NULL if given phi node must be handled by means of
>>>>>>> extended phi node predication. If number of predecessors of phi-block
>>>>>>> is equal 2 and atleast one incoming edge is not critical original
>>>>>>> algorithm is used.
>>>>>>> (get_predicate_for_edge): New function.
>>>>>>> (find_insertion_point): New function.
>>>>>>> (predicate_arbitrary_scalar_phi): New function.
>>>>>>> (predicate_all_scalar_phis): Introduce new variable BEFORE.
>>>>>>> Invoke find_insertion_point to initialize gsi and
>>>>>>> predicate_arbitrary_scalar_phi if TRUE_BB is NULL - it signals
>>>>>>> that extended predication must be applied).
>>>>>>> (insert_gimplified_predicates): Add test for non-predicated basic
>>>>>>> blocks that there are no gimplified statements to insert. Insert
>>>>>>> predicates at the block begining for extended if-conversion.
>>>>>>> (tree_if_conversion): Initialize flag_force_vectorize from current
>>>>>>> loop or outer loop (to support pragma omp declare).Do loop versioning
>>>>>>> for innermost loop marked with pragma omp simd and
>>>>>>> FLAG_TREE_LOOP_IF_CONVERT was not sett-up. Nullify 'aux' field of edges
>>>>>>> for blocks with two successors.
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>> 2014-09-08 17:10 GMT+04:00 Richard Biener <richard.guenther@gmail.com>:
>>>>>>>> On Fri, Aug 15, 2014 at 2:02 PM, Yuri Rumyantsev <ysrumyan@gmail.com> wrote:
>>>>>>>>> Richard!
>>>>>>>>> Here is updated patch with the following changes:
>>>>>>>>>
>>>>>>>>> 1. Any restrictions on phi-function were eliminated for extended conversion.
>>>>>>>>> 2.  Put predicate for critical edges to 'aux' field of edge, i.e.
>>>>>>>>> negate_predicate was deleted.
>>>>>>>>> 3. Deleted splitting of critical edges, i.e. both outgoing edges can
>>>>>>>>> be critical.
>>>>>>>>> 4. Use notion of cd-equivalence to set-up predicate for join basic
>>>>>>>>> blocks to simplify it.
>>>>>>>>> 5. I decided to not design pre-pass since it will lead generating
>>>>>>>>> chain of cond expressions for phi-node if conversion, whereas for phi
>>>>>>>>> of kind
>>>>>>>>>   x = PHI <1(2), 1(3), 2(4)>
>>>>>>>>> only one cond expression is required and this is considered as simple
>>>>>>>>> optimization for arbitrary phi-function. More precise,
>>>>>>>>> if phi-function have only two different arguments and one of them has
>>>>>>>>> single occurrence, if- conversion is performed as if phi have only 2
>>>>>>>>> arguments.
>>>>>>>>> For arbitrary phi function a chain of cond expressions is produced.
>>>>>>>>>
>>>>>>>>> Updated patch is attached.
>>>>>>>>>
>>>>>>>>> Any comments will be appreciated.
>>>>>>>>
>>>>>>>> The patch is still very big and does multiple things at once which makes
>>>>>>>> it hard to review.
>>>>>>>>
>>>>>>>> In addition to that it changes function singatures without updating
>>>>>>>> the function comments.  For example what is the convert_bool
>>>>>>>> argument doing to add_to_dst_predicate_list?  Why do we need
>>>>>>>> all this added logic.
>>>>>>>>
>>>>>>>> You duplicate operand_equal_for_phi_arg_p.
>>>>>>>>
>>>>>>>> I think the code handling PHIs with more than two operands but
>>>>>>>> only two unequal operands is useful generally, so that's an obvious
>>>>>>>> candidate for splitting out into a separate patch.
>>>>>>>>
>>>>>>>> +   CONVERT_BOOL argument was added to convert bool predicate computations
>>>>>>>> +   which is not supported by vectorizer to int type through creating of
>>>>>>>> +   conditional expressions.  */
>>>>>>>>
>>>>>>>> Example?  The vectorizer has patterns for bool predicate computations.
>>>>>>>> This seems to be another feature that needs splitting out.
>>>>>>>>
>>>>>>>> The way you get around the critical edge parts looks awkward to me.
>>>>>>>> Please either do _all_ predicates as edge predicates or simply
>>>>>>>> split critical edges (of the respective loop body).
>>>>>>>>
>>>>>>>> I still think that an utility doing same PHI arg merging by introducing
>>>>>>>> forwarder blocks would be nicer to have.
>>>>>>>>
>>>>>>>> I'd restructure the main tree_if_conversion function to apply these
>>>>>>>> CFG pre-transforms when we are going to version the loop
>>>>>>>> for if conversion (eventually transitioning to always doing that).
>>>>>>>>
>>>>>>>> So - please split up the patch.  It's way too big.
>>>>>>>>
>>>>>>>> Thanks,
>>>>>>>> Richard.
>>>>>>>>
>>>>>>>>> 2014-08-15  Yuri Rumyantsev  <ysrumyan@gmail.com>
>>>>>>>>>
>>>>>>>>> * tree-if-conv.c (cgraph.h): Add include file to detect function clone.
>>>>>>>>> (flag_force_vectorize): New variable.
>>>>>>>>> (edge_predicate): New function.
>>>>>>>>> (set_edge_predicate): New function.
>>>>>>>>> (add_stmt_to_bb_predicate_gimplified_stmts): New function.
>>>>>>>>> (init_bb_predicate): Add initialization of negate_predicate field.
>>>>>>>>> (reset_bb_predicate): Reset negate_predicate to NULL_TREE.
>>>>>>>>> (convert_name_to_cmp): New function.
>>>>>>>>> (get_type_for_cond): New function.
>>>>>>>>> (convert_bool_predicate): New function.
>>>>>>>>> (predicate_disjunction): New function.
>>>>>>>>> (predicate_conjunction): New function.
>>>>>>>>> (add_to_predicate_list): Add convert_bool argument.
>>>>>>>>> Use predicate of cd-equivalent block if convert_bool is true and
>>>>>>>>> such bb exists; save it in static variable for further possible use.
>>>>>>>>> Add call of predicate_disjunction if convert_bool argument is true.
>>>>>>>>> (add_to_dst_predicate_list): Add convert_bool argument.
>>>>>>>>> Add early function exit if edge target block is always executed.
>>>>>>>>> Add call of predicate_conjunction if convert_bool argument is true.
>>>>>>>>> Pass convert_bool argument for add_to_predicate_list.
>>>>>>>>> Set-up predicate for crritical edge if convert_bool is true.
>>>>>>>>> (equal_phi_args): New function.
>>>>>>>>> (phi_has_two_different_args): New function.
>>>>>>>>> (if_convertible_phi_p): Accept phi nodes with more than two args
>>>>>>>>> if flag_force_vectorize wa set-up.
>>>>>>>>> (ifcvt_can_use_mask_load_store): Add test on flag_force_vectorize.
>>>>>>>>> (if_convertible_stmt_p): Allow calls of function clones if
>>>>>>>>> flag_force_vectorize was set-up.
>>>>>>>>> (all_edges_are_critical): New function.
>>>>>>>>> (if_convertible_bb_p): Allow bb has more than two predecessors if
>>>>>>>>> flag_force_vectorize was set-up. Use call of all_edges_are_critical
>>>>>>>>> to reject block if-conversion with imcoming critical edges only if
>>>>>>>>> flag_force_vectorize was not set-up.
>>>>>>>>> (walk_cond_tree): New function.
>>>>>>>>> (vect_bool_pattern_is_applicable): New function.
>>>>>>>>> (predicate_bbs): Add convert_bool argument which is used to transform
>>>>>>>>> comparison expressions of boolean type into conditional expressions
>>>>>>>>> with integral operands. If convert_bool argument was set-up and
>>>>>>>>> vect bool pattern can be appied perform the following transformation:
>>>>>>>>> (bool) x != 0  --> y = (int) x; x != 0;
>>>>>>>>> Add check that if fold_build2 produces bool conversion if convert_bool
>>>>>>>>> was set-up, recompute predicate using build2_loc. Additional argument
>>>>>>>>> 'convert_bool" is passed to add_to_dst_predicate_list and
>>>>>>>>> add_to_predicate_list.
>>>>>>>>> (if_convertible_loop_p_1): Recompute POST_DOMINATOR tree if
>>>>>>>>> flag_force_vectorize was set-up to calculate cd equivalent bb's.
>>>>>>>>> Call predicate_bbs with additional argument equal to false.
>>>>>>>>> (find_phi_replacement_condition): Extend function interface:
>>>>>>>>> it returns NULL if given phi node must be handled by means of
>>>>>>>>> extended phi node predication. If number of predecessors of phi-block
>>>>>>>>> is equal 2 and atleast one incoming edge is not critical original
>>>>>>>>> algorithm is used.
>>>>>>>>> (is_cond_scalar_reduction): Add 'extended' argument which signals that
>>>>>>>>> phi arguments must be evaluated through phi_has_two_different_args.
>>>>>>>>> (predicate_scalar_phi): Add invoÑation of convert_name_to_cmp if cond
>>>>>>>>> is SSA_NAME. Add 'false' argument to call of is_cond_scalar_reduction.
>>>>>>>>> (get_predicate_for_edge): New function.
>>>>>>>>> (find_insertion_point): New function.
>>>>>>>>> (predicate_arbitrary_phi): New function.
>>>>>>>>> (predicate_extended_scalar_phi): New function.
>>>>>>>>> (predicate_all_scalar_phis): Add code to set-up gimple statement
>>>>>>>>> iterator for predication of extended scalar phi's for insertion.
>>>>>>>>> (insert_gimplified_predicates): Add test for non-predicated basic
>>>>>>>>> blocks that there are no gimplified statements to insert. Insert
>>>>>>>>> predicates at the block begining for extended if-conversion.
>>>>>>>>> (predicate_mem_writes): Invoke convert_name_to_cmp for extended
>>>>>>>>> predication to build mask.
>>>>>>>>> (combine_blocks): Pass flag_force_vectorize to predicate_bbs.
>>>>>>>>> (tree_if_conversion): Initialize flag_force_vectorize from current
>>>>>>>>> loop or outer loop (to support pragma omp declare).Do loop versioning
>>>>>>>>> for innermost loop marked with pragma omp simd.
>>>>>>>>>
>>>>>>>>> 2014-08-01 13:40 GMT+04:00 Richard Biener <richard.guenther@gmail.com>:
>>>>>>>>>> On Wed, Jun 25, 2014 at 4:06 PM, Yuri Rumyantsev <ysrumyan@gmail.com> wrote:
>>>>>>>>>>> Hi All,
>>>>>>>>>>>
>>>>>>>>>>> We implemented additional support for pragma omp simd in part of
>>>>>>>>>>> extended if-conversion loops with such pragma. These extensions
>>>>>>>>>>> include:
>>>>>>>>>>>
>>>>>>>>>>> 1. All extensions are performed only if considered loop or its outer
>>>>>>>>>>>    loop was marked with pragma omp simd (force_vectorize); For ordinary
>>>>>>>>>>>    loops behavior was not changed.
>>>>>>>>>>> 2. Took off cfg restriction on basic block which can have more than 2
>>>>>>>>>>>    predecessors.
>>>>>>>>>>> 3. Put additional restriction on phi nodes which was missed in current design:
>>>>>>>>>>>    all phi nodes must be in non-predicated basic block to conform
>>>>>>>>>>>    semantic of COND_EXPR which is used for transformation.
>>>>>>>>>>
>>>>>>>>>> How is that so?  If the PHI is predicated then its result will be used
>>>>>>>>>> in a PHI node again and thus we'd create a sequence of COND_EXPRs.
>>>>>>>>>>
>>>>>>>>>> No?
>>>>>>>>>>
>>>>>>>>>>> 4. Extend predication of phi nodes: phi may have more than 2 arguments
>>>>>>>>>>> with some limitations:
>>>>>>>>>>>    - for phi nodes which have more than 2 arguments, but only two
>>>>>>>>>>>    arguments are different and one of them has the only occurence,
>>>>>>>>>>> transformation to  single COND_EXPR can be done.
>>>>>>>>>>>    - if phi node has more different arguments and all edge predicates
>>>>>>>>>>>    correspondent to phi-arguments are disjoint, a chain of COND_EXPR
>>>>>>>>>>>    will be generated for it. In current design very simple check is used:
>>>>>>>>>>>    check starting from end that two edges correspondent to neighbor
>>>>>>>>>>> arguments have common predecessor which is used for further check
>>>>>>>>>>> with next edge.
>>>>>>>>>>>  These guarantee that phi predication will produce the correct result.
>>>>>>>>>>
>>>>>>>>>> Btw, you can think of these extensions as unfactoring a PHI node by
>>>>>>>>>> inserting forwarder blocks.  Thus
>>>>>>>>>>
>>>>>>>>>>    x = PHI <1(2), 1(3), 2(4)>
>>>>>>>>>>
>>>>>>>>>> becomes
>>>>>>>>>>
>>>>>>>>>>   bb 5: <forwarder-from(2)-and(3)>
>>>>>>>>>>
>>>>>>>>>>   x = PHI <1(5), 2(4)>
>>>>>>>>>>
>>>>>>>>>> and
>>>>>>>>>>
>>>>>>>>>>   x = PHI <1(2), 2(3), 3(4)>
>>>>>>>>>>
>>>>>>>>>> becomes
>>>>>>>>>>
>>>>>>>>>>   bb 5:
>>>>>>>>>>   x' = PHI <1(2), 2(3)>
>>>>>>>>>>
>>>>>>>>>>   b = PHI<x'(5), 3(4)>
>>>>>>>>>>
>>>>>>>>>> which means that 3) has to work.  Note that we want this kind of
>>>>>>>>>> PHI transforms for out-of-SSA as well to reduce the number of
>>>>>>>>>> copies we need to insert on edges.
>>>>>>>>>>
>>>>>>>>>> Thus it would be nice if you implemented 4) in terms of a pre-pass
>>>>>>>>>> over the force_vect loops PHI nodes, applying that CFG transform.
>>>>>>>>>> And make 3) work properly if it doesn't already.
>>>>>>>>>>
>>>>>>>>>> It looks like you introduce a "negate predicate" to work around the
>>>>>>>>>> critical edge limitation?  Please instead change if-conversion to
>>>>>>>>>> work with edge predicates (as opposed to BB predicates).
>>>>>>>>>>
>>>>>>>>>> Thanks,
>>>>>>>>>> Richard.
>>>>>>>>>>
>>>>>>>>>>>
>>>>>>>>>>> Here is example of such extended predication (compile with -march=core-avx2):
>>>>>>>>>>> #pragma omp simd safelen(8)
>>>>>>>>>>>   for (i=0; i<512; i++)
>>>>>>>>>>>   {
>>>>>>>>>>>     float t = a[i];
>>>>>>>>>>>     if (t > 0 & t < 1.0e+17f)
>>>>>>>>>>>       if (c[i] != 0)
>>>>>>>>>>> res += 1;
>>>>>>>>>>>   }
>>>>>>>>>>>   <bb 4>:
>>>>>>>>>>>   # res_15 = PHI <res_1(5), 0(3)>
>>>>>>>>>>>   # i_16 = PHI <i_11(5), 0(3)>
>>>>>>>>>>>   # ivtmp_17 = PHI <ivtmp_14(5), 512(3)>
>>>>>>>>>>>   t_5 = a[i_16];
>>>>>>>>>>>   _6 = t_5 > 0.0;
>>>>>>>>>>>   _7 = t_5 < 9.9999998430674944e+16;
>>>>>>>>>>>   _8 = _7 & _6;
>>>>>>>>>>>   _ifc__28 = (unsigned int) _8;
>>>>>>>>>>>   _10 = &c[i_16];
>>>>>>>>>>>   _ifc__36 = _ifc__28 != 0 ? 4294967295 : 0;
>>>>>>>>>>>   _9 = MASK_LOAD (_10, 0B, _ifc__36);
>>>>>>>>>>>   _ifc__29 = _ifc__28 != 0 ? 1 : 0;
>>>>>>>>>>>   _ifc__30 = (int) _ifc__29;
>>>>>>>>>>>   _ifc__31 = _9 != 0 ? _ifc__30 : 0;
>>>>>>>>>>>   _ifc__32 = _ifc__28 != 0 ? 1 : 0;
>>>>>>>>>>>   _ifc__33 = (int) _ifc__32;
>>>>>>>>>>>   _ifc__34 = _9 == 0 ? _ifc__33 : 0;
>>>>>>>>>>>   _ifc__35 = _ifc__31 != 0 ? 1 : 0;
>>>>>>>>>>>   res_1 = res_15 + _ifc__35;
>>>>>>>>>>>   i_11 = i_16 + 1;
>>>>>>>>>>>   ivtmp_14 = ivtmp_17 - 1;
>>>>>>>>>>>   if (ivtmp_14 != 0)
>>>>>>>>>>>     goto <bb 4>;
>>>>>>>>>>>
>>>>>>>>>>> Bootstrap and regression testing did not show any new failures.
>>>>>>>>>>>
>>>>>>>>>>> gcc/ChageLog
>>>>>>>>>>>
>>>>>>>>>>> 2014-06-25  Yuri Rumyantsev  <ysrumyan@gmail.com>
>>>>>>>>>>>
>>>>>>>>>>> * tree-if-conv.c (flag_force_vectorize): New variable.
>>>>>>>>>>> (struct bb_predicate_s): Add negate_predicate field.
>>>>>>>>>>> (bb_negate_predicate): New function.
>>>>>>>>>>> (set_bb_negate_predicate): New function.
>>>>>>>>>>> (bb_copy_predicate): New function.
>>>>>>>>>>> (add_stmt_to_bb_predicate_gimplified_stmts): New function.
>>>>>>>>>>> (init_bb_predicate): Add initialization of negate_predicate field.
>>>>>>>>>>> (reset_bb_predicate): Reset negate_predicate to NULL_TREE.
>>>>>>>>>>> (convert_name_to_cmp): New function.
>>>>>>>>>>> (get_type_for_cond): New function.
>>>>>>>>>>> (convert_bool_predicate): New function.
>>>>>>>>>>> (predicate_disjunction): New function.
>>>>>>>>>>> (predicate_conjunction): New function.
>>>>>>>>>>> (add_to_predicate_list): Add convert_bool argument.
>>>>>>>>>>> Add call of predicate_disjunction if convert_bool argument is true.
>>>>>>>>>>> (add_to_dst_predicate_list): Add convert_bool argument.
>>>>>>>>>>> Add early function exit if edge target block is always executed.
>>>>>>>>>>> Add call of predicate_conjunction if convert_bool argument is true.
>>>>>>>>>>> Pass convert_bool argument for add_to_predicate_list.
>>>>>>>>>>> (equal_phi_args): New function.
>>>>>>>>>>> (phi_has_two_different_args): New function.
>>>>>>>>>>> (phi_args_disjoint): New function.
>>>>>>>>>>> (if_convertible_phi_p): Accept phi nodes with more than two args
>>>>>>>>>>> for loops marked with pragma omp simd. Add check that phi nodes are
>>>>>>>>>>> in non-predicated basic blocks.
>>>>>>>>>>> (ifcvt_can_use_mask_load_store): Use flag_force_vectorize.
>>>>>>>>>>> (all_edges_are_critical): New function.
>>>>>>>>>>> (if_convertible_bb_p): Allow bb has more than two predecessors if
>>>>>>>>>>> flag_force_vectorize was setup. Use call of all_edges_are_critical
>>>>>>>>>>> to reject block if-conversion with imcoming critical edges only if
>>>>>>>>>>> flag_force_vectorize was not setup.
>>>>>>>>>>> (walk_cond_tree): New function.
>>>>>>>>>>> (vect_bool_pattern_is_applicable): New function.
>>>>>>>>>>> (predicate_bbs): Add convert_bool argument that is used to transform
>>>>>>>>>>> comparison expressions of boolean type into conditional expressions
>>>>>>>>>>> with integral operands. If bool_conv argument is false or both
>>>>>>>>>>> outgoing edges are not critical old algorithm of predicate assignments
>>>>>>>>>>> is used, otherwise the following code was added: check on applicable
>>>>>>>>>>> of vect-bool-pattern recognition and trnasformation of
>>>>>>>>>>> (bool) x != 0  --> y = (int) x; x != 0;
>>>>>>>>>>> compute predicates for both outgoing edges one of which is critical
>>>>>>>>>>> one using 'normal' edge, i.e. compute true and false predicates using
>>>>>>>>>>> normal outgoing edge only; evaluated predicates are stored in
>>>>>>>>>>> predicate and negate_predicate fields of struct bb_predicate_s and
>>>>>>>>>>> negate_predicate of normal edge conatins predicate of critical edge,
>>>>>>>>>>> but generated gimplified statements are stored in their destination
>>>>>>>>>>> block fields. Additional argument 'convert_bool" is passed to
>>>>>>>>>>> add_to_dst_predicate_list and add_to_predicate_list.
>>>>>>>>>>> (if_convertible_loop_p_1): Call predicate_bbs with additional argument
>>>>>>>>>>> equal to false.
>>>>>>>>>>> (find_phi_replacement_condition): Extend function interface:
>>>>>>>>>>> it returns NULL if given phi node must be handled by means of
>>>>>>>>>>> extended phi node predication. If number of predecessors of phi-block
>>>>>>>>>>> is equal 2 and atleast one incoming edge is not critical original
>>>>>>>>>>> algorithm is used.
>>>>>>>>>>> (is_cond_scalar_reduction): Add 'extended' argument which signals that
>>>>>>>>>>> both phi arguments must be evaluated through phi_has_two_different_args.
>>>>>>>>>>> (predicate_scalar_phi): Add invoÑation of convert_name_to_cmp if cond
>>>>>>>>>>> is SSA_NAME. Add 'false' argument to call of is_cond_scalar_reduction.
>>>>>>>>>>> (get_predicate_for_edge): New function.
>>>>>>>>>>> (find_insertion_point): New function.
>>>>>>>>>>> (predicate_phi_disjoint_args): New function.
>>>>>>>>>>> (predicate_extended_scalar_phi): New function.
>>>>>>>>>>> (predicate_all_scalar_phis): Add code to set-up gimple statement
>>>>>>>>>>> iterator for predication of extended scalar phi's for insertion.
>>>>>>>>>>> (insert_gimplified_predicates): Add test for non-predicated basic
>>>>>>>>>>> blocks that there are no gimplified statements to insert. Insert
>>>>>>>>>>> predicates at the block begining for extended if-conversion.
>>>>>>>>>>> (predicate_mem_writes): Invoke convert_name_to_cmp for extended
>>>>>>>>>>> predication to build mask.
>>>>>>>>>>> (combine_blocks): Pass flag_force_vectorize to predicate_bbs.
>>>>>>>>>>> (split_crit_edge): New function.
>>>>>>>>>>> (tree_if_conversion): Initialize flag_force_vectorize from current
>>>>>>>>>>> loop or outer loop (to support pragma omp declare). Invoke
>>>>>>>>>>> split_crit_edge for extended predication. Do loop versioning for
>>>>>>>>>>> innermost loop marked with pragma omp simd.