proven larger than the loop-count
This fixes PR31098: Try to resolve statically data-dependences whose
compile-time-unknown distance can be proven larger than the loop-count,
instead of resorting to runtime dependence checking (which are not always
possible).
For vectorization it is sufficient to prove that the dependence distance
is >= VF; But in some cases we can prune unknown dependence distances early,
and even before selecting the VF, and without a runtime test, by comparing
the distance against the loop iteration count. Since the vectorized code
will be executed only if LoopCount >= VF, proving distance >= LoopCount
also guarantees that distance >= VF. This check is also equivalent to the
Strong SIV Test.
Reviewers: mkuper, anemet, sanjoy
Differential Revision: https://reviews.llvm.org/D28044
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@294892 91177308-0d34-0410-b5e6-96231b3b80d8
Note that require<domtree> and require<loops> aren't needed because they
come in implicitly via the loop pass manager.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@274712 91177308-0d34-0410-b5e6-96231b3b80d8
