[llvm] [AArch64] Don't add runtime SCEV checks from containsDecreasingPointers. (PR #216961)

[Mel Chen via llvm-commits]

https://github.com/Mel-Chen approved this pull request.

LG
Notice this comment:
```
// We call this to discover whether any load/store pointers in the loop have
// negative strides. This will require extra work to reverse the loop
// predicate, which may be expensive.
```
IIUC, reversing the predicate is only required when stride = -1. Is containsDecreasingPointer being overly conservative here?

https://github.com/llvm/llvm-project/pull/216961