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c0d18b6696
speculate. Without this, loop rotate (among many other places) would suddenly stop working in the presence of debug info. I found this looking at loop rotate, and have augmented its tests with a reduction out of a very hot loop in yacr2 where failing to do this rotation costs sometimes more than 10% in runtime performance, perturbing numerous downstream optimizations. This should have no impact on performance without debug info, but the change in performance when debug info is enabled can be extreme. As a consequence (and this how I got to this yak) any profiling of performance problems should be treated with deep suspicion -- they may have been wildly innacurate of debug info was enabled for profiling. =/ Just a heads up. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@154263 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))
//===---------------------------------------------------------------------===//