[PATCH] D13677: [IR] Fix bug in `ConstantRange::intersectWith`

[Sanjoy Das via llvm-commits]

sanjoy created this revision.
sanjoy added a reviewer: nlewycky.
sanjoy added a subscriber: llvm-commits.

NOTE: this is still failing tests, so it isn't yet ready to go in and is
a WIP.  The failing tests will have to be audited manually before
checking this in.

NOTE: all of the fixes in `ConstantRangeTest.cpp` were bugs to begin
with, AFAICT.

This "fixes" a bug in `intersectWith` by rewriting it.  The idea is that
we can extend the bitwidth of a constant range by a bit and use that to
simplify the logic around checking for wrapped ranges.

Roughly, if this is our number line with a wrapped range

  |---)----[-------|

we map the wrapped range to

  |--------[-------|---)------------|  .. (A)

and if this is the number line with an not-wrapped range

  |---[----)-------|

we map it to

  |---[----)-------|----------------|  .. (B)

or

  |----------------|---[----)-------|  .. (C)

When intersecting a wrapped range with an unwrapped one (the "hard"
case), we intersect (A) with (B) and (A) with (C); and pick the larger
of the two.

We can do the same thing for unions.

http://reviews.llvm.org/D13677

Files:
  lib/IR/ConstantRange.cpp
  unittests/IR/ConstantRangeTest.cpp

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