Partial attempt at improved aliasing information for LLVM.
Merge branch 'master' into better-aliasing-info
Cleaned up TBAA for constant indices.
Removed trick to keep FFT input/output buffers cached.
Removed handling for negative bases and asserted instead.
Merge branch 'master' into better-aliasing-info
Merge pull request #436 from halide/better-aliasing-info

Better aliasing info