[PATCH] D35347: [IRCE] Fix corner case with Start = INT_MAX

[Max Kazantsev via Phabricator via llvm-commits]

mkazantsev created this revision.

When iterating through loop

  for (int i = INT_MAX; i > 0; i--)

We fail to generate the pre-loop for it. It happens because we use the overflown value
in a comparison predicate when identifying whether or not we need it.

In old logic, we used SLE predicate against Greatest value which exceeds all seen values
of the IV and might be overflown. Now we use the GreatestSeen value of this IV with SLT
predicate.

Also added a test that ensures that a pre-loop is generated for such loops.


https://reviews.llvm.org/D35347

Files:
  lib/Transforms/Scalar/InductiveRangeCheckElimination.cpp
  test/Transforms/IRCE/pre_post_loops.ll

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