Re: Do not give realistic estimates for loop with array accesses

[Bernhard Reutner-Fischer <rep.dot.nop@gmail.com>]

On March 30, 2016 2:36:14 PM GMT+02:00, Richard Biener <rguenther@suse.de> wrote:
>On Wed, 30 Mar 2016, Jan Hubicka wrote:
>
>> > 
>> > You are only changing one place in this file.
>> 
>> You are right. I am attaching the updated patch which I am re-testing
>now.
>> > 
>> > The vectorizer already checks this (albeit indirectly):
>> > 
>> >   HOST_WIDE_INT max_niter
>> >     = max_stmt_executions_int (LOOP_VINFO_LOOP (loop_vinfo));
>> >   if ((LOOP_VINFO_NITERS_KNOWN_P (loop_vinfo)
>> >        && (LOOP_VINFO_INT_NITERS (loop_vinfo) <
>vectorization_factor))
>> >       || (max_niter != -1
>> >           && (unsigned HOST_WIDE_INT) max_niter <
>vectorization_factor))
>> >     {
>> >       if (dump_enabled_p ())
>> >         dump_printf_loc (MSG_MISSED_OPTIMIZATION, vect_location,
>> >                          "not vectorized: iteration count smaller
>than "
>> >                          "vectorization factor.\n");
>> >       return false;
>> >     }
>> 
>> Yes, but one tests only vectorization_factor and other
>min_profitable_estimate
>> which probably should be greater than vectorization_factor.
>> 
>> The check above should therefore become redundant.  My reading of the
>code is
>> that min_profiltable_estimate is computed after the check above, so
>it is
>> probably an useful shortcut and the message is also bit more
>informative.
>> I updated the later test to use max_niter variable once it is
>computed.
>> 
>> OK with those changes assuming testing passes?
>
>Ok.

Maybe s/overlow/overflow/g while at it..

TIA,
>
>Richard.
>
>> Honza
>> 
>> 	* tree-ssa-loop-niter.c (idx_infer_loop_bounds): We can't get
>realistic
>> 	estimates here.
>> 	* tree-ssa-loop-unswitch.c (tree_unswitch_single_loop): Use also
>> 	max_loop_iterations_int.
>> 	(tree_unswitch_outer_loop): Likewise.
>> 	* tree-ssa-loop-ivopts.c (avg_loop_niter): Likewise.
>> 	* tree-vect-loop.c (vect_analyze_loop_2): Likewise.
>> Index: tree-ssa-loop-ivopts.c
>> ===================================================================
>> --- tree-ssa-loop-ivopts.c	(revision 234516)
>> +++ tree-ssa-loop-ivopts.c	(working copy)
>> @@ -121,7 +121,11 @@ avg_loop_niter (struct loop *loop)
>>  {
>>    HOST_WIDE_INT niter = estimated_stmt_executions_int (loop);
>>    if (niter == -1)
>> -    return AVG_LOOP_NITER (loop);
>> +    {
>> +      niter = max_stmt_executions_int (loop);
>> +      if (niter == -1 || niter > AVG_LOOP_NITER (loop))
>> +        return AVG_LOOP_NITER (loop);
>> +    }
>>  
>>    return niter;
>>  }
>> Index: tree-ssa-loop-niter.c
>> ===================================================================
>> --- tree-ssa-loop-niter.c	(revision 234516)
>> +++ tree-ssa-loop-niter.c	(working copy)
>> @@ -3115,7 +3115,6 @@ idx_infer_loop_bounds (tree base, tree *
>>    tree low, high, type, next;
>>    bool sign, upper = true, at_end = false;
>>    struct loop *loop = data->loop;
>> -  bool reliable = true;
>>  
>>    if (TREE_CODE (base) != ARRAY_REF)
>>      return true;
>> @@ -3187,14 +3186,14 @@ idx_infer_loop_bounds (tree base, tree *
>>        && tree_int_cst_compare (next, high) <= 0)
>>      return true;
>>  
>> -  /* If access is not executed on every iteration, we must ensure
>that overlow may
>> -     not make the access valid later.  */
>> +  /* If access is not executed on every iteration, we must ensure
>that overlow
>> +     may not make the access valid later.  */
>>    if (!dominated_by_p (CDI_DOMINATORS, loop->latch, gimple_bb
>(data->stmt))
>>        && scev_probably_wraps_p (initial_condition_in_loop_num (ev,
>loop->num),
>>  				step, data->stmt, loop, true))
>> -    reliable = false;
>> +    upper = false;
>>  
>> -  record_nonwrapping_iv (loop, init, step, data->stmt, low, high,
>reliable, upper);
>> +  record_nonwrapping_iv (loop, init, step, data->stmt, low, high,
>false, upper);
>>    return true;
>>  }
>>  
>> Index: tree-ssa-loop-unswitch.c
>> ===================================================================
>> --- tree-ssa-loop-unswitch.c	(revision 234516)
>> +++ tree-ssa-loop-unswitch.c	(working copy)
>> @@ -223,6 +223,8 @@ tree_unswitch_single_loop (struct loop *
>>        /* If the loop is not expected to iterate, there is no need
>>  	 for unswitching.  */
>>        iterations = estimated_loop_iterations_int (loop);
>> +      if (iterations < 0)
>> +        iterations = max_loop_iterations_int (loop);
>>        if (iterations >= 0 && iterations <= 1)
>>  	{
>>  	  if (dump_file && (dump_flags & TDF_DETAILS))
>> @@ -439,6 +441,8 @@ tree_unswitch_outer_loop (struct loop *l
>>    /* If the loop is not expected to iterate, there is no need
>>        for unswitching.  */
>>    iterations = estimated_loop_iterations_int (loop);
>> +  if (iterations < 0)
>> +    iterations = max_loop_iterations_int (loop);
>>    if (iterations >= 0 && iterations <= 1)
>>      {
>>        if (dump_file && (dump_flags & TDF_DETAILS))
>> Index: tree-vect-loop.c
>> ===================================================================
>> --- tree-vect-loop.c	(revision 234516)
>> +++ tree-vect-loop.c	(working copy)
>> @@ -2063,6 +2063,8 @@ start_over:
>>  
>>    estimated_niter
>>      = estimated_stmt_executions_int (LOOP_VINFO_LOOP (loop_vinfo));
>> +  if (estimated_niter != -1)
>> +    estimated_niter = max_niter;
>>    if (estimated_niter != -1
>>        && ((unsigned HOST_WIDE_INT) estimated_niter
>>            <= MAX (th, (unsigned)min_profitable_estimate)))
>> 
>>