llvm/lib/Analysis
Andrew Trick 31f61e8b22 IVUsers should only generate SCEV's for values that are safe to speculate.
This allows SCEVExpander to run on the IV expressions.

This codifies an assumption made by LSR to complete the fix for
PR11356, but I haven't been able to generate a separate unit test for
this part. I'm adding it as an extra safety check.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@160204 91177308-0d34-0410-b5e6-96231b3b80d8
2012-07-13 23:33:05 +00:00
..
2012-05-10 23:38:07 +00:00
2012-06-29 09:01:47 +00:00
2012-05-17 20:27:58 +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.

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

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))

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