[PATCH] CFLAA Bugfix -- Tag untrackable pointers (inttoptr/ptrtoint)

[George Burgess IV]

Hi dberlin, hfinkel,

// Hal already LGTM'ed this for style, I'm putting it here so any discussions about design are published, as requested. :)

This patch notes that pointers passed to inttoptr/ptrtoint can escape. 

- Used StratifiedAttrs instead of one-way edges because StratifiedAttrs don't union everything (the advantage of one-way edges), and we get propagation of the Unknown attribute to sets "below" the Unknown one for free.

- Explicitly omitted from this patch: special handling of Unknown StratifiedAttrs. An Unknown attribute on some set only forces a MayAlias if the set it's being compared to has any StratifiedAttrs set (interacts with an argument not marked as noalias, a global, or inttoptr/ptrtoint). I can't see how this can be broken, but feedback is appreciated.

http://reviews.llvm.org/D8098

Files:
  lib/Analysis/CFLAliasAnalysis.cpp
  test/Analysis/CFLAliasAnalysis/branch-alias.ll

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