[Bug c/71539] incomplete execution of a nested loop for -O2 and -O3

[cubitect at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=71539

--- Comment #2 from cubitect at gmail dot com ---
Thank you for the tip! I was unaware that signed integer overflow is undefined
in standard C. I was rewriting some java code in C when I ran into this
problem, so this makes sense now. (Though I still don't see how this caused the
loop to abort prematurely.)