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Fedor Sergeev
a51f09141c
Summary: Loop-pass printing is somewhat deficient since it does not provide the context around the loop (e.g. preheader). This context information becomes pretty essential when analyzing transformations that move stuff out of the loop. Extending printLoop to cover preheader and exit blocks (if any). Reviewers: sanjoy, silvas, weimingz Reviewed By: sanjoy Subscribers: apilipenko, skatkov, llvm-commits Differential Revision: https://reviews.llvm.org/D40246 git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@318878 91177308-0d34-0410-b5e6-96231b3b80d8
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))
//===---------------------------------------------------------------------===//