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Re: Hopelessly broken loop_father, loop_depth


On Mon, Aug 13, 2012 at 12:22 PM, Richard Guenther
<richard.guenther@gmail.com> wrote:
> On Mon, Aug 13, 2012 at 12:21 PM, Richard Guenther
> <richard.guenther@gmail.com> wrote:
>> On Sun, Aug 12, 2012 at 2:02 PM, Steven Bosscher <stevenb.gcc@gmail.com> wrote:
>>> On Sat, Aug 11, 2012 at 11:16 PM, Steven Bosscher <stevenb.gcc@gmail.com> wrote:
>>>> Lots of test cases fail with the attached patch.
>>>
>>> Lots still fail after correcting the verifier :-)
>>>
>>> 920723-1.c: In function 'f':
>>> 920723-1.c:14:1: error: bb 13 has loop depth 2, should be 1
>>>  f (int count, vector_t * pos, double r, double *rho)
>>>  ^
>>> 920723-1.c:14:1: error: bb 14 has loop depth 2, should be 1
>>> 920723-1.c:14:1: internal compiler error: in verify_loop_structure, at
>>> cfgloop.c:1598
>>
>> That's a pre-existing bug in unswitching.  When unswitching
>> simplifies the condition it unswitches on using simplify_using_entry_checks
>> it may turn an inner loop into an exit to an endless loop.  But it does
>> not modify the loop stucture according to this change.
>>
>> void foo (int x, int r)
>> {
>> loop4:
>>   if (r >= x)
>>     {
>>       goto loop4_latch;
>>     }
>>   else
>>     {
>> loop5:
>>       if (r >= x)
>>         goto loop4_latch;
>>       goto loop5;
>>     }
>> loop4_latch:
>>   goto loop4;
>> }
>>
>> simplified testcase that even fails at -O1.  We mostly rely on cfg-cleanup
>> to fixup loops for us, so this is one case it does not handle properly.
>
> Actually that testcase fails verification right after a full loop
> discovery which
> DOM1 performs ...

Fixed by attached patch.

>> The quest of keeping loops up-to-date is hard ... but thanks for the checking
>> code ;)

Which probably still makes things fail elsewhere ;)

Richard.

>> Richard.
>>
>>> Ciao!
>>> Steven

Attachment: fix-loops-1
Description: Binary data


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