[PATCH] Improve BasicAA CS-CS queries

[hfinkel at anl.gov]

Hi aschwaighofer, sunfish,

BasicAA contains knowledge of certain intrinsics, such as memcpy and memset, and uses that information to form more-accurate answers to CallSite vs. Loc ModRef queries. Unfortunately, it does not use this information when answering CallSite vs. CallSite queries.

Generically, when an intrinsic takes one or more pointers and the intrinsic is marked only to read/write from its arguments, the offset/size is unknown. As a result, the generic code that answers CallSite vs. CallSite (and CallSite vs. Loc) queries in AA uses UnknownSize when forming Locs from an intrinsic's arguments. While BasicAA's CallSite vs. Loc override could use more-accurate size information for some intrinsics, it did not do the same for CallSite vs. CallSite queries.

This patch refactors the intrinsic-specific logic in BasicAA into a generic AA query function: getArgLocation, which is overridden by BasicAA to supply the intrinsic-specific knowledge, and used by AA's generic implementation. This allows the intrinsic-specific knowledge to be used by both CallSite vs. Loc and CallSite vs. CallSite queries, and simplifies the BasicAA implementation.

Currently, only one function, Mac's memset_pattern16, is handled by BasicAA (all the rest are intrinsics). As a side-effect of this refactoring, BasicAA's getModRefBehavior override now also returns OnlyAccessesArgumentPointees for this function (which is an improvement).

http://reviews.llvm.org/D4342

Files:
  include/llvm/Analysis/AliasAnalysis.h
  lib/Analysis/AliasAnalysis.cpp
  lib/Analysis/BasicAliasAnalysis.cpp
  lib/Analysis/NoAliasAnalysis.cpp
  test/Analysis/BasicAA/cs-cs.ll
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