Re: [PATCH, PR69110] Don't return NULL access_fns in dr_analyze_indices

[Richard Biener <rguenther@suse.de>]

On January 23, 2016 7:44:23 PM GMT+01:00, Sebastian Pop <sebpop@gmail.com> wrote:
>On Sat, Jan 23, 2016 at 12:28 PM, Tom de Vries <Tom_deVries@mentor.com>
>wrote:
>> That was my original patch, and Richard commented: 'I think avoiding
>a NULL
>> access_fns is ok but it should be done unconditionally, not only for
>the
>> DECL_P case'. In order words, he asked me to do the exact opposite of
>the
>> change you now propose.
>>
>
>In the case of a DECL_P it is correct to say that it has an access
>function of 0.
>In the graphite testcase it is not correct to say that the access
>function for a given data reference is zero:
>we only initialize access_fns in the case of a polynomial chrec:
>
>  if (TREE_CODE (ref) == MEM_REF)
>    {
>      op = TREE_OPERAND (ref, 0);
>      access_fn = analyze_scalar_evolution (loop, op);
>      access_fn = instantiate_scev (before_loop, loop, access_fn);
>      if (TREE_CODE (access_fn) == POLYNOMIAL_CHREC)
>        {
>[...]
>           access_fns.safe_push (access_fn);
>        }
>    }
>
>In all other cases we may not have a representation of the access
>functions.
>It is incorrect to initialize to "A[0]" all those data references that
>cannot be analyzed.

But does it matter as the base will not be equal with one that can be analyzed?

>If needed, instead of returning vNULL, one could initialize the vector
>to empty:
>
>if (access_fns == vNULL)
>  access_fns.create (0);
>
>and that would be correct, though it would not teach the dependence
>analysis
>how to deal with the global variable access function in pr69110.
>I think the fix is to add the zero subscript only for DECL_P (ref).
>
>Sebastian