Re: [PATCH GCC][V2]A simple implementation of loop interchange

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

On Thu, Nov 30, 2017 at 3:51 PM, Richard Biener
<richard.guenther@gmail.com> wrote:
> On Thu, Nov 30, 2017 at 4:09 PM, Richard Biener
> <richard.guenther@gmail.com> wrote:
>> On Thu, Nov 30, 2017 at 3:13 PM, Bin.Cheng <amker.cheng@gmail.com> wrote:
>>> On Thu, Nov 30, 2017 at 1:01 PM, Richard Biener
>>> <richard.guenther@gmail.com> wrote:
>>
>> Ok, I'd like to "dumb" the pass down to the level we can solve the
>> bwave case (which I realize is already one of the more complicated ones).
>>
>> Just because it's already late for GCC 8.
>
> For reference I'll commit the following tomorrow, will play with adding
> a testcase for bwaves and doing the multiple_of_p thing we talked about.
Given instantiated scev in parameterized case like:
{{{p_19(D), +, 8}_1, +, (long unsigned int) n_16(D) * 8}_2, +, (long
unsigned int) (n_16(D) * n_16(D)) * 8}_3
it's ideal if we can relate the variable part in stride with loop
niters.  Unfortunately that's impractical because niter
computation and address computation may expand variables differently.
 As in case of bwaves.
This leaves us the method to check multiple relation for stride itself:
(long unsigned int) (n_16(D) * n_16(D)) * 8  ;;stride X
 vs.
(long unsigned int) n_16(D) * 8                     ;;stride Y
 vs.
8                                                                    ;;stride Z
From inner loop to outer, we check if Y is multiple of Z and if X is
multiple of Y, so strides computed are like:
8 * AVG_LOOP_NITERS * AVG_LOOP_NITERS
 vs.
8 * AVG_LOOP_NITERS
 vs.
8

To make it general, we also need to check if X is multiple of previous
stride (Z, in this case) if check on Y failed.

The multiple check on tree expr is weak, so one question is how to do
if failed.  Giving up or using a placeholder const stride?

Thanks,
bin
>
> Richard.