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Re: Hopelessly broken loop_father, loop_depth


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 ...

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


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