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7063c7e084
Gather an array of interesting dependences rather than just failing after the first unsafe one and regarding the loop unsafe. Loop Distribution needs to be able to collect all dependences in order to isolate the dependence cycles into their own partition. Since the dependence checking algorithm is quadratic in terms of accesses sharing the same underlying pointer, I am applying a cut-off threshold (MaxInterestingDependence). Exceeding that, the logic reverts back to the original approach deeming the loop unsafe upon encountering the first unsafe dependence. The main idea of the patch is to split isDepedent from directly answering the question whether the dep is safe for vectorization to return a dependence type which then gets mapped to old boolean result using Dependence::isSafeForVectorization. Tested that this was compile-time neutral on SpecINT2006 LTO bitcode inputs. No assembly change on the testsuite including external. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@231806 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))
//===---------------------------------------------------------------------===//