What is the explanation for “warning: assuming that the loop is not infinite”

Question

I had just taken the decision to change as many variables from unsigned to int and upon recompiling the code in question, was greeted by this warning m

Answer 1

According to this GCC patch from 2005, it appears that GCC is performing an "unsafe loop optimization" (and you are being warned because -funsafe-loop-optimizations is set). If the loop is infinite, this particular optimization will fail somehow.

Since you said it is a terminating loop, it sounds as though you have nothing to worry about.

Another relevant part of the patch:

@opindex Wunsafe-loop-optimizations
Warn if the loop cannot be optimized because the compiler could not
assume anything on the bounds of the loop indices.  With
@option{-funsafe-loop-optimizations} warn if the compiler made
+such assumptions.