[Bug tree-optimization/64277] [4.9/5 Regression] Incorrect warning "array subscript is above array bounds"

[enkovich.gnu at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64277

--- Comment #9 from Ilya Enkovich <enkovich.gnu at gmail dot com> ---
Nice solution for this problem would be to have a better estimation of maximum
loop iterations number.  Currently array size and index step are used to get
the maximum ignoring starting index value range.

Another way to solve the problem is to disable warnings for code generated by
cunroll in case it cannot compute exact number of iterations.  I attach a patch
which does it.

This bug is hit multiple times on Android build with GCC 4.9.  With this fix we
have a clean Android build with GCC 4.9.