Re: Regression with recent change

[Jeff Law <jeffreyalaw@gmail.com>]

On 9/13/2021 7:29 AM, Aldy Hernandez wrote:
> Jeff has pointed out that after my change adding global ranges to the
> path solver, torture/pr55107.c is failing.  Before I start digging
> deep into the IL, I'd like to make sure this is not either expected or
> a bogus test.
>
> Compiling this test on x86 with -Wall yields:
>
> $ gcc -c -O2 pr55107.c -Wall
> pr55107.c: In function ‘f’:
> pr55107.c:32:51: warning: the omitted middle operand in ‘?:’ will
> always be ‘true’, suggest explicit middle operand [-Wparentheses]
>     32 |       ((a = d) ? b = 0 : (**p ? : 1) != (d != 1 ? : (a = 0)))
> != (k ? a : 0)
>        |                                                   ^
> pr55107.c:33:11: warning: suggest parentheses around comparison in
> operand of ‘!=’ [-Wparentheses]
>     32 |       ((a = d) ? b = 0 : (**p ? : 1) != (d != 1 ? : (a = 0)))
> != (k ? a : 0)
>        |
>    ~~~~~~~~~~~
>     33 |           < (a *= c = k) && (**p = 0);
>        |           ^~~~~~~~~~~~~~
> pr55107.c:33:16: warning: operation on ‘a’ may be undefined [-Wsequence-point]
>     33 |           < (a *= c = k) && (**p = 0);
>        |                ^~
> pr55107.c:33:16: warning: operation on ‘a’ may be undefined [-Wsequence-point]
> pr55107.c:33:26: warning: value computed is not used [-Wunused-value]
>     33 |           < (a *= c = k) && (**p = 0);
>        |                          ^~
> pr55107.c:17:14: warning: ‘j’ is used uninitialized [-Wuninitialized]
>     17 |       for (; *j; j++)
>        |              ^~
>
> So it looks like there's some undefined behavior going on, even before
> my patch.  I'd like to get some feedback, because this is usually the
> type of problems I see in the presence of a smarter threader... things
> get shuffled around, problematic code gets isolated, and warning
> passes have an easier time (or sometimes harder time) diagnosing
> things.
The original issue was PRE hanging, so I'd lean towards keeping the test 
as-is and instead twiddling any warning flags we can to make the 
diagnostics go away.

jeff