Dan Gohman 28287794d4 Teach ScalarEvolution to simplify smax and umax when it can prove
that one operand is always greater than another.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@101142 91177308-0d34-0410-b5e6-96231b3b80d8
2010-04-13 16:51:03 +00:00
..
2010-04-08 18:52:18 +00:00
2010-04-12 02:22:30 +00:00
2010-04-09 01:39:53 +00:00

Analysis Opportunities:

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In test/Transforms/LoopStrengthReduce/quadradic-exit-value.ll, the
ScalarEvolution expression for %r is this:

  {1,+,3,+,2}<loop>

Outside the loop, this could be evaluated simply as (%n * %n), however
ScalarEvolution currently evaluates it as

  (-2 + (2 * (trunc i65 (((zext i64 (-2 + %n) to i65) * (zext i64 (-1 + %n) to i65)) /u 2) to i64)) + (3 * %n))

In addition to being much more complicated, it involves i65 arithmetic,
which is very inefficient when expanded into code.

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