[Bug tree-optimization] Fix for PR71994

[Richard Biener]

On Tue, Jul 26, 2016 at 5:13 AM, kugan
<kugan.vivekanandarajah@linaro.org> wrote:
> Hi,
>
> For testcase in pr71994, type of bb conditional result and the type of the
> PHI stmt are different (as om.0_1 is int and the first PHI argument is
> _bool; PHI stmt uses a constant zero that comes from edge 2). Therefore when
> we optimize final range test stmt, we end up setting integer 1 for other PHI
> argument. This results in ICE.
>
>   <bb 2>:
>   om.0_1 = om;
>   _2 = om.0_1 >= 0;
>   int _3 = (int) _2;
>   if (om.0_1 != 0)
>     goto <bb 3>;
>   else
>     goto <bb 4>;
>
>   <bb 3>:
>   int _4 = om.0_1 & _3;
>   _Bool _12 = _4 != 0;
>   <bb 4>:
>
>   # _Bool _13 = PHI <0(2), _12(3)>
>
>
> IMHO, the fix should be that, we should check the type before replacing the
> value (punt otherwise). Attached patch does that. Bootstrapped and
> regression tested on x86_64-linux-gnu with no new regressions. Is this OK
> for trunk?

Ugh, this is undocumented spaghetti code I am not familiar with.  I
can't see if it
is safe to truncate a constant here so I'd feel safer to just punt instead.

Richard.

> Thanks,
> Kugan
>
> gcc/testsuite/ChangeLog:
>
> 2016-07-26  Kugan Vivekanandarajah  <kuganv@linaro.org>
>
>         * gcc.dg/torture/pr71994.c: New test.
>
> gcc/ChangeLog:
>
> 2016-07-26  Kugan Vivekanandarajah  <kuganv@linaro.org>
>
>         * tree-ssa-reassoc.c (maybe_optimize_range_tests): Check type
> compatibility.
>