[sledge] Strengthen simplification of xor terms
[sledge] Strengthen simplification of xor terms

Summary:
And refactor fragile pattern matching to avoid missing function
symbols going forward.

Reviewed By: peterogithub

Differential Revision: D31129946

fbshipit-source-id: 976e3ab5d

facebook/infer,jvillard/infer,jvillard/infer,facebook/infer,facebook/infer,facebook/infer,facebook/infer,facebook/infer,facebook/infer,jvillard/infer,jvillard/infer,jvillard/infer,jvillard/infer,jvillard/infer