[Bug sanitizer/82072] sanitizer does not detect an overflow from LLONG_MIN

[mpolacek at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=82072

--- Comment #12 from Marek Polacek <mpolacek at gcc dot gnu.org> ---
(In reply to Vittorio Zecca from comment #10)
> A related issue is the following:
> 
> /* UB sanitizer should detect undefined negation of LLONG_MIN */
> /* must be compiled with -fsanitize=undefined and run */
> #include <limits.h>
> int main()
> {
> long long int llnum=LLONG_MIN;
> unsigned  int unum;
> unum = - llnum;/*negation of -9223372036854775808 cannot be represented in
> type 'long long int'*/
> return 0;
> }
> 
> Or should I open a new bug?

This is related.  Due to case NEGATE_EXPR: in convert_to_integer_1:

 913               return convert (type,
 914                               fold_build1 (ex_form, typex,
 915                                            convert (typex,
 916                                                     TREE_OPERAND (expr,
0))));

instead of 
unum = (unsigned int) -llnum;
we create
unum = -(unsigned int) llnum;
hiding the overflow.