This is the mail archive of the gcc-patches@gcc.gnu.org mailing list for the GCC project.


Index Nav: [Date Index] [Subject Index] [Author Index] [Thread Index]
Message Nav: [Date Prev] [Date Next] [Thread Prev] [Thread Next]
Other format: [Raw text]

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


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.

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.

Attachment: if-conv.patch2.new
Description: Binary data


Index Nav: [Date Index] [Subject Index] [Author Index] [Thread Index]
Message Nav: [Date Prev] [Date Next] [Thread Prev] [Thread Next]