As shown in D82998, the basic-aa-recphi option can cause miscompiles for gep's with negative constants. The option checks for recursive phi, that recurse through a contant gep. If it finds one, it performs aliasing calculations using the other phi operands with an unknown size, to specify that an unknown number of elements after the initial value are potentially accessed. This works fine expect where the constant is negative, as the size is still considered to be positive. So this patch checks to make sure that the constant is also positive.
I will not attempt to turn the option back on until after the branch is made next week, to give us lots of time to catch anything else. But this should hopefully fix the issues.