[PATCH] D31238: [ScalarEvolution] Re-enable Predicate implication from operations

[Max Kazantsev via Phabricator via llvm-commits]

mkazantsev created this revision.
Herald added subscribers: mehdi_amini, mzolotukhin.

The patch https://reviews.llvm.org/rL298481 was reverted due to crash on clang-with-lto-ubuntu build.
The reason of the crash was type mismatch between either a or b and RHS in the following situation:

  LHS = sext(a +nsw b) > RHS.

This is quite rare, but still possible situation. Normally we need to cast all {a, b, RHS} to their widest type.
But we try to avoid creation of new SCEV that are not constants to avoid initiating recursive analysis that
can take a lot of time and/or cache a bad value for iterations number. To deal with this, in this patch we
reject this case and will not try to analyze it if the type of sum doesn't match with the type of RHS. In this
situation we don't need to create any non-constant SCEVs.

This patch also adds an assertion to the method IsProvedViaContext so that we could fail on it and not
go further into range analysis etc (because in some situations these analyzes succeed even when the passed
arguments have wrong types, what should not normally happen).


https://reviews.llvm.org/D31238

Files:
  include/llvm/Analysis/ScalarEvolution.h
  lib/Analysis/ScalarEvolution.cpp
  test/Analysis/ScalarEvolution/scev-division.ll

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