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78dce2577d
Summary: This approach has two major advantages over the existing one: 1. We don't need to extend bitwidth in our computations. Extending bitwidth is a big issue for compile time as we often end up working with APInts wider than 64bit, which is a slow case for APInt. 2. When we zero extend a wrapped range, we lose some information (we replace the range with [0, 1 << src bit width)). Thus, avoiding such extensions better preserves information. Correctness testing: I ran 'ninja check' with assertions that the new implementation of getRangeForAffineAR gives the same results as the old one (this functionality is not present in this patch). There were several failures - I inspected them manually and found out that they all are caused by the fact that we're returning more accurate results now (see bullet (2) above). Without such assertions 'ninja check' works just fine, as well as SPEC2006. Compile time testing: CTMark/Os: - mafft/pairlocalalign -16.98% - tramp3d-v4/tramp3d-v4 -12.72% - lencod/lencod -11.51% - Bullet/bullet -4.36% - ClamAV/clamscan -3.66% - 7zip/7zip-benchmark -3.19% - sqlite3/sqlite3 -2.95% - SPASS/SPASS -2.74% - Average -5.81% Performance testing: The changes are expected to be neutral for runtime performance. Reviewers: sanjoy, atrick, pete Subscribers: llvm-commits Differential Revision: https://reviews.llvm.org/D30477 git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@297992 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))
//===---------------------------------------------------------------------===//