Re: [RFC][PR82479] missing popcount builtin detection

["Bin.Cheng" <amker.cheng@gmail.com>]

On Fri, Jun 1, 2018 at 9:56 AM, Kugan Vivekanandarajah
<kugan.vivekanandarajah@linaro.org> wrote:
> Hi Bin,
>
> Thanks a lo for the review.
>
> On 1 June 2018 at 03:45, Bin.Cheng <amker.cheng@gmail.com> wrote:
>> On Thu, May 31, 2018 at 3:51 AM, Kugan Vivekanandarajah
>> <kugan.vivekanandarajah@linaro.org> wrote:
>>> Hi Bin,
>>>
>>> Thanks for the review. Please find the revised patch based on the
>>> review comments.
>>>
>>> Thanks,
>>> Kugan
>>>
>>> On 17 May 2018 at 19:56, Bin.Cheng <amker.cheng@gmail.com> wrote:
>>>> On Thu, May 17, 2018 at 2:39 AM, Kugan Vivekanandarajah
>>>> <kugan.vivekanandarajah@linaro.org> wrote:
>>>>> Hi Richard,
>>>>>
>>>>> On 6 March 2018 at 02:24, Richard Biener <richard.guenther@gmail.com> wrote:
>>>>>> On Thu, Feb 8, 2018 at 1:41 AM, Kugan Vivekanandarajah
>>>>>> <kugan.vivekanandarajah@linaro.org> wrote:
>>>>>>> Hi Richard,
>>>>>>>
>>
>> Hi,
>> Thanks very much for working.
>>
>>> +/* Utility function to check if OP is defined by a stmt
>>> +   that is a val - 1.  If that is the case, set it to STMT.  */
>>> +
>>> +static bool
>>> +ssa_defined_by_and_minus_one_stmt_p (tree op, tree val, gimple **stmt)
>> This is checking if op is defined as val - 1, so name it as
>> ssa_defined_by_minus_one_stmt_p?
>>
>>> +{
>>> +  if (TREE_CODE (op) == SSA_NAME
>>> +      && (*stmt = SSA_NAME_DEF_STMT (op))
>>> +      && is_gimple_assign (*stmt)
>>> +      && (gimple_assign_rhs_code (*stmt) == PLUS_EXPR)
>>> +      && val == gimple_assign_rhs1 (*stmt)
>>> +      && integer_minus_onep (gimple_assign_rhs2 (*stmt)))
>>> +    return true;
>>> +  else
>>> +    return false;
>> You can simply return the boolean condition.
> Done.
>
>>
>>> +}
>>> +
>>> +/* See if LOOP is a popcout implementation of the form
>> ...
>>> +  rhs1 = gimple_assign_rhs1 (and_stmt);
>>> +  rhs2 = gimple_assign_rhs2 (and_stmt);
>>> +
>>> +  if (ssa_defined_by_and_minus_one_stmt_p (rhs1, rhs2, &and_minus_one))
>>> +    rhs1 = rhs2;
>>> +  else if (ssa_defined_by_and_minus_one_stmt_p (rhs2, rhs1, &and_minus_one))
>>> +    ;
>>> +  else
>>> +    return false;
>>> +
>>> +  /* Check the recurrence.  */
>>> +  phi = SSA_NAME_DEF_STMT (gimple_assign_rhs1 (and_minus_one));
>> So gimple_assign_rhs1 (and_minus_one) == rhs1 is always true?  Please
>> use rhs1 directly.
>
> Done.
>>> +  gimple *src_phi = SSA_NAME_DEF_STMT (rhs2);
>> I think this is checking wrong thing and is redundant.  Either rhs2
>> equals to rhs1 or is defined as (rhs1 - 1).  For (rhs2 == rhs1) case,
>> the check duplicates checking on phi; for the latter, it's never a PHI
>> stmt and shouldn't be checked.
>>
>>> +  if (gimple_code (phi) != GIMPLE_PHI
>>> +      || gimple_code (src_phi) != GIMPLE_PHI)
>>> +    return false;
>>> +
>>> +  dest = gimple_assign_lhs (count_stmt);
>>> +  tree fn = builtin_decl_implicit (BUILT_IN_POPCOUNT);
>>> +  tree src = gimple_phi_arg_def (src_phi, loop_preheader_edge (loop)->dest_idx);
>>> +  if (adjust)
>>> +    iter = fold_build2 (MINUS_EXPR, TREE_TYPE (dest),
>>> +            build_call_expr (fn, 1, src),
>>> +            build_int_cst (TREE_TYPE (dest), 1));
>>> +  else
>>> +    iter = build_call_expr (fn, 1, src);
>> Note tree-ssa-loop-niters.c always use unsigned_type_for (IV-type) as
>> niters type.  Though unsigned type is unnecessary in this case, but
>> better to follow existing behavior?
>
> Done.
>>
>>> +  max = int_cst_value (TYPE_MAX_VALUE (TREE_TYPE (dest)));
>> As richi suggested, max should be the number of bits in type of IV.
>>
>>> +
>>> +  niter->assumptions = boolean_false_node;
>> Redundant.
>
> Not sure I understand. If I remove this,  I am getting ICE
> (segmentation fault). What is the expectation here?
Is it a simple typo?  Because assumptions is set to boolean_true_node
just 5 lines below?
The niters part looks good for me with this change.  You may need
richi's approval for other parts?

Thanks,
bin
>
>>> +  niter->control.base = NULL_TREE;
>>> +  niter->control.step = NULL_TREE;
>>> +  niter->control.no_overflow = false;
>>> +  niter->niter = iter;
>>> +  niter->assumptions = boolean_true_node;
>>> +  niter->may_be_zero = boolean_false_node;
>>> +  niter->max = max;
>>> +  niter->bound = NULL_TREE;
>>> +  niter->cmp = ERROR_MARK;
>>> +  return true;
>>> +}
>>> +
>>> +
>> Appology if these are nitpickings.
> Thanks for the review. I am happy to make the changes needed to get it
> to how it should be :)
>
> Thanks,
> Kugan
>
>>
>> Thanks,
>> bin