Jesse Natalie authored Jul 15, 2020 and Erik Faye-Lund committed Aug 05, 2020

Clang/llvm generates a unique constant sampler for every read call
which references them, rather than based on variable declarations.
That causes us to end up with a bunch of identical variables.

This pass dedupes them by pointing all tex ops that reference a
constant sampler to the same one, and removing dead derefs. After
removing dead uniform variables, we'll only have unique constant samplers.