mirror of
https://github.com/llvm/llvm-project.git
synced 2025-05-06 04:16:07 +00:00
eed6531ea2
Summary: Compute the strongly connected components of the CFG and fall back to use these for blocks that are in loops that are not detected by LoopInfo when computing loop back-edge and exit branch probabilities. Reviewers: dexonsmith, davidxl Subscribers: mcrosier, llvm-commits Differential Revision: https://reviews.llvm.org/D39385 llvm-svn: 317094
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))
//===---------------------------------------------------------------------===//