[PATCH] D23214: [MDA] Treat invariant.start as non-dependence

[Anna Thomas via llvm-commits]

anna updated this revision to Diff 67159.
anna added a comment.

[Alias Analysis] Mark invariant.start as readonly

We teach alias analysis that invariant.start is readonly.
This helps with GVN and memcopy optimizations that currently treat.
invariant.start as a clobber.
We need to treat this as readonly, so that DSE does not incorrectly
remove stores prior to the invariant.start

This initially started off as a change to teach MDA about invariant.start,
but further discussion prompted the change to alias analysis (where other such
special cases for guards and assume intrinsics exist).


https://reviews.llvm.org/D23214

Files:
  lib/Analysis/BasicAliasAnalysis.cpp
  test/Transforms/DeadStoreElimination/invariant.start.ll
  test/Transforms/GVN/invariant.start.ll
  test/Transforms/MemCpyOpt/invariant.start.ll

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