Re: [C++ Patch / RFC] PR 45385

[Jason Merrill]

I think the fix for 35602 was wrong; instead of trying to suppress the 
warning, we should avoid building expressions that trip it.  In this 
case, the problem is a type mismatch in build_vec_init between 
maxindex/iterator (ptrdiff_type_node) and array_type_nelts_total 
(sizetype).  And indeed, converting (ptrdiff_t)-1 to unsigned changes 
its sign.

I think a better fix for 35602 would be to bail out of build_vec_init 
exit early if maxindex is -1.

Jason