Duncan P. N. Exon Smith 2033057de8 Revert "blockfreq: Rewrite BlockFrequencyInfoImpl" (#2)
This reverts commit r206666, as planned.

Still stumped on why the bots are failing.  Sanitizer bots haven't
turned anything up.  If anyone can help me debug either of the failures
(referenced in r206666) I'll owe them a beer.  (In the meantime, I'll be
auditing my patch for undefined behaviour.)

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@206677 91177308-0d34-0410-b5e6-96231b3b80d8
2014-04-19 00:42:46 +00:00
..
2014-04-17 22:26:44 +00:00
2014-04-17 22:26:44 +00:00

Analysis Opportunities:

//===---------------------------------------------------------------------===//

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.

//===---------------------------------------------------------------------===//

In formatValue in test/CodeGen/X86/lsr-delayed-fold.ll,

ScalarEvolution is forming this expression:

((trunc i64 (-1 * %arg5) to i32) + (trunc i64 %arg5 to i32) + (-1 * (trunc i64 undef to i32)))

This could be folded to

(-1 * (trunc i64 undef to i32))

//===---------------------------------------------------------------------===//