Use SCEV to check if the minimum iteration check (TC < Step) is known to
be false.
This is a first step towards addressing
https://github.com/llvm/llvm-project/issues/111098. To catch the exact
case from the issue, we need to do extra work to make sure the wrap
flags on the shl are preserved and used by SCEV.
Note that skeleton creation will be gradually moved to VPlan and this
simplification should be done as VPlan transform eventually. The current
plan is to move skeleton creation to VPlan starting from parts closest
to the parts already created by VPlan, starting with induction resume
value creation (started with
https://github.com/llvm/llvm-project/pull/110577), then memory and SCEV
checks and finally minimum iteration checks.
PR: https://github.com/llvm/llvm-project/pull/111310
We only version unknown strides to 1. If the original type is i1, then
the sign of the extension matters. Properly extend the stride value
before replacing it.
Fixes https://github.com/llvm/llvm-project/issues/91369.
