mirror of
https://github.com/RPCS3/llvm.git
synced 2026-07-19 15:13:49 -04:00
Chandler Carruth
8d16ccbe0f
isDescendantOf methods on RefSCCs in terms of the forward edges rather than the parent sets. This is technically slower, but probably not interestingly slower, and all of these routines were already so expensive that they're guarded behind both !NDEBUG and EXPENSIVE_CHECKS. This removes another non-critical usage of parent sets. I've also added some comments to try and help clarify to any potential users the costs of these routines. They're mostly useful for debugging, asserts, or other queries. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@310170 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))
//===---------------------------------------------------------------------===//