[Bug c++/84816] [7.2.0/8.0.1 x86_64] Incorrect code generation if signed overflow

[dlesnikov at hotmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=84816

--- Comment #7 from Dmitry Lesnikov <dlesnikov at hotmail dot com> ---
(In reply to Andrew Pinski from comment #5)
> (In reply to Dmitry Lesnikov from comment #4)
> > (In reply to Andrew Pinski from comment #1)
> > > signed overflow is undefined behavior at runtime.
> > 
> > for(int i=0; i<10; i++)
> > 
> > this loop is correct.
> 
> But there is an overflow with the variable a when i is 6.

Why does the line
C1 c1;
affect the behavior of the loop?