Hi all,
I've committed this and with one more change.
--- gcc/loop-iv.c (revision 272731)
+++ gcc/loop-iv.c (working copy)
@@ -3004,7 +3004,7 @@ find_simple_exit (struct loop *loop, struct niter_
well. It results in incorrect predicate information on the exit condition
expression. For example, if says [(int) _1 + -8, + , -8] != 0 finite,
it means _1 can exactly divide -8. */
- if (single_exit (loop) && finite_loop_p (loop))
+ if (desc->infinite && single_exit (loop) && finite_loop_p (loop))
{
desc->infinite = NULL_RTX;
if (dump_file)
on 2019/6/26 上午11:45, Kewen.Lin wrote:
> Hi Jeff,
>
> on 2019/6/26 上午5:49, Jeff Law wrote:
>> On 6/25/19 3:41 AM, Kewen.Lin wrote:
>>> Hi Richard,
>>>
>>> Thanks a lot for review comments.
>>>
>>> on 2019/6/25 下午3:23, Richard Biener wrote:
>>>> On Tue, 25 Jun 2019, Kewen.Lin wrote:
>>>>
>>>>> Hi all,
>>>>>
>>>>>
>>>>> It's based on two observations:
>>>>> 1) the loop structure for one specific loop is shared between
>>>>> middle-end and
>>>>> back-end.
>>>>> 2) for one specific loop, if it's finite then never become infinite
>>>>> itself.
>>>>>
>>>>> As one gcc newbie, I'm not sure whether these two observations are true
>>>>> in all
>>>>> cases. Please feel free to correct me if anything missing.
>>>>
>>>> I think 2) is not true with -ffinite-loops.
>>>
>>> I just looked at the patch on this option, I don't fully understand it can
>>> affect
>>> 2). It's to take one loop as finite with any normal exit, can some loop
>>> with this
>>> assertion turn into infinite later by some other analysis?
>>>
>>>>
>>>>> btw, I also took a look at how the loop constraint LOOP_C_FINITE is used,
>>>>> I think
>>>>> it's not suitable for this purpose, it's mainly set by vectorizer and
>>>>> tell niter
>>>>> and scev to take one loop as finite. The original patch has the words
>>>>> "constraint flag is mainly set by consumers and affects certain semantics
>>>>> of
>>>>> niter analyzer APIs".
>>>>>
>>>>> Bootstrapped and regression testing passed on
>>>>> powerpc64le-unknown-linux-gnu.
>>>>
>>>> Did you consider to simply use finite_loop_p () from doloop.c? That
>>>> would be a much simpler patch.
>>>
>>> Good suggestion! I took it for granted that the function can be only
>>> efficient in
>>> middle-end, but actually some information like bit any_upper_bound could be
>>> kept to
>>> RTL.
>>>
>>>>
>>>> For the testcase in question -ffinite-loops would provide this guarantee
>>>> even on RTL, so would the upper bound that may be still set.
>>>>
>>>> Richard.
>>>>
>>>
>>> The new version with Richard's suggestion listed below.
>>> Regression testing is ongoing.
>>>
>>>
>>> Thanks,
>>> Kewen
>>>
>>> -----------
>>>
>>> gcc/ChangeLog
>>>
>>> 2019-06-25 Kewen Lin <[email protected]>
>>>
>>> PR target/62147
>>> * gcc/loop-iv.c (find_simple_exit): Call finite_loop_p to update
>>> finiteness.
>>>
>>> gcc/testsuite/ChangeLog
>>>
>>> 2019-06-25 Kewen Lin <[email protected]>
>>>
>>> PR target/62147
>>> * gcc.target/powerpc/pr62147.c: New test.
>> This is fine assuming regression testing was OK.
>>
>
> Thanks Jeff! Bootstrapped and regression testing passed on
> powerpc64le-unknown-linux-gnu.
>
>> One might argue that "finite_loop_p" belongs elsewhere since it's not
>> really querying tree/gimple structures.
>
> I guess it will do something gimple specific (estimate_numbers_of_iterations)
> when it can
> so it was placed there.
>
>
> Thanks,
> Kewen
>
>>
>> jeff
>>
>
