NVPTXAliasAnalysis extends the default AA to take pointer address spaces
into account. The analysis assumes that pointers in different address
spaces do not alias, unless one of them is generic (flat) address
space.
The patch also implements pointsToConstantMemory (via getModRefInfoMask)
to expose semantic of the constant address space to the optimizer
as discussed in D112466.
param->generic is not implemented yet, so this is overly conservative.
Do we have any way to check whether ASC(param->generic) is available? If we do, we could use it to determine if we should return MayAlias or NoAlias.