[Bug c++/31268] New: Non-deterministic bug producing a run-time infinite loop

[sylvain dot pion at sophia dot inria dot fr]

It took me several hours to try to extract a usable test-case for this issue,
so I hope you will be able to make sense out of it.

The problem : compiling with current g++ 4.2, with -O2, makes the attached
program loop infinitely, while it is not expected to.

It does not loop with g++ 4.3 or older versions than 4.2.  It also does not
loop when adding -fno-strict-aliasing with g++ 4.2, or when compiling with
-O only.

Even more strange : it does not loop when I remove some unused bits of
the program (which is why I had a hard time shrinking it down), for example
unused typedefs (look for "limb2").

The relevant part of the program is a small class (MP_Float) containing an
std::vector<short>, and some code around it, namely the operator_minus()
function which is called, and which loops.

I attach the pre-processed file, as well as the main small file so that you
can see what is the relevant part of it, and decide if it is a compiler bug
or an issue with my program.  My program does some type conversions, which
may be the source of the problem (triggering undefined behavior ?), but they
seem fine to me.


-- 
           Summary: Non-deterministic bug producing a run-time infinite loop
           Product: gcc
           Version: 4.2.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: sylvain dot pion at sophia dot inria dot fr
  GCC host triplet: i686-pc-linux-gnu


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=31268