[Bug rtl-optimization/66552] Missed optimization when shift amount is result of signed modulus

[helijia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66552

--- Comment #13 from Li Jia He <helijia at gcc dot gnu.org> ---
In this optimization we assume n is either positive or divisible by the nth
power of 2.
So the result of the % is non-negative.  However, it is not reasonable for
translating (a % 32)) to (a & 31).  If a is signed int and value is -1, (a %
32) will get the follow result, (a %  32) = (-1 % 32) = -1. However, (a & 31)
will get the follow result, (a & 31) = -1 & 31 = 31.  This conversion is not
reasonable at this time.