[SCEV] Check if predicate is known false for predicated AddRecs. (#151134)

Similarly to https://github.com/llvm/llvm-project/pull/131538, we can
also try and check if a predicate is known to wrap given the backedge
taken count.

For now, this just checks directly when we try to create predicated
AddRecs. This both helps to avoid spending compile-time on optimizations
where we know the predicate is false, and can also help to allow
additional vectorization (e.g. by deciding to scalarize memory accesses
when otherwise we would try to create a predicated AddRec with a
predicate that's always false).

The initial version is quite restricted, but can be extended in
follow-ups to cover more cases.

PR: https://github.com/llvm/llvm-project/pull/151134
2 files changed
tree: 1d684e7233c20140c8b340a74ddcfe2ff5841086
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  9. flang/
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  35. CODE_OF_CONDUCT.md
  36. CONTRIBUTING.md
  37. LICENSE.TXT
  38. pyproject.toml
  39. README.md
  40. SECURITY.md
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