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c96b33c2f4
Summary: This is obviously an interesting case because it may motivate code restructuring or LTO. Reporting this requires instantiation of ORE in the loop where the call sites are first gathered. I've checked compile-time overhead *with* -Rpass-with-hotness and the worst slow-down was 6% in mcf and quickly tailing off. As before without -Rpass-with-hotness there is no overhead. Because this could be a pretty noisy diagnostics, it is currently qualified as 'verbose'. As of this patch, 'verbose' diagnostics are only emitted with -Rpass-with-hotness, i.e. when the output is expected to be filtered. Reviewers: eraman, chandlerc, davidxl, hfinkel Subscribers: tejohnson, Prazek, davide, llvm-commits Differential Revision: https://reviews.llvm.org/D23415 git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@279860 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))
//===---------------------------------------------------------------------===//