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


On Mon, Jul 14, 2014 at 12:16 PM, Yuri Rumyantsev <ysrumyan@gmail.com> wrote:
> Ping!

It's in my queue (pretty large patch for a drive-by review - maybe there is
an opportunity to split the patch up?).

Won't get to it before the Cauldron though.

Richard.

> 2014-06-25 18:06 GMT+04:00 Yuri Rumyantsev <ysrumyan@gmail.com>:
>> 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.
>> 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.
>>
>> 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.


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