Improve a test by replacing undef with poison, and regenerate it using
UpdateTestChecks.

Test needed updating due to changes on main since branch was tested.

When adding a new predicate to a union predicate, some of the existing
predicates may be implied by the new predicate. Remove any existing
predicates that are already implied by the new predicate.

Depends on https://github.com/llvm/llvm-project/pull/118184 to show the
main benefit.

PR: https://github.com/llvm/llvm-project/pull/118185

Loop Optimizations expect the input loop to be in LCSSA form. But it
seems that LoopVersioning doesn't have any check to see if the loop is
actually in LCSSA form. As a result, if we give it a loop which is not
in LCSSA form but still correct semantically, the resulting
transformation fails to pass through verifier pass with the following
error.

Instruction does not dominate all uses!
%inc = add nsw i16 undef, 1
store i16 %inc, ptr @c, align 1

As the loop is not in LCSSA form, LoopVersioning's transformations leads
to invalid IR! As some instructions do not dominate all their uses.

This patch checks if a loop is in LCSSA form, if not it will call
formLCSSARecursively on the loop before passing it to LoopVersioning.

Fixes: #36998 

If we have a pointer AddRec, the maximum increment is
2^(pointer-index-wdith - 1) - 1. This means that if incrementing the
AddRec wraps, the distance between the previously accessed location and
the wrapped location is > 2^(pointer-index-wdith - 1), i.e. if the GEP
for the AddRec is inbounds, this would be poison due to the object being
larger than half the pointer index type space. The poison would be
immediate UB when the memory access gets executed..

Similar reasoning can be applied for decrements.

PR: https://github.com/llvm/llvm-project/pull/113126

isNoWrap has exactly one caller which handles Assume = true separately,
but too conservatively. Instead, pass Assume to isNoWrap, so it is
threaded into getPtrStride, which has the correct handling for the
Assume flag. Also note that the Stride == 1 check in isNoWrap is
incorrect: getPtrStride returns Strides == 1 or -1, except when
isNoWrapAddRec or Assume are true, assuming ShouldCheckWrap is true; we
can include the case of -1 Stride, and when isNoWrapAddRec is true. With
this change, passing Assume = true to getPtrStride could return a
non-unit stride, and we correctly handle that case as well.

When expanding SCEV adds to geps, transfer the nuw flag to the resulting
gep. (Note that this doesn't apply to IV increment GEPs, which go
through a different code path.)

After pr96656.ll were added to LAA and LoopVersioning, it was decided
that the bug is in a caller of LoopVersioning, not in LAA or
LoopVersioning itself. The new candidate was LoopLoadElim, but #96656
has since been marked invalid. Hence, re-organize the added tests to
avoid confusion, and the testcase from the investigation to
LoopLoadElim.

The issue is in LoopAccessAnalysis, but the regression was seen in the
user LoopVersioning. Hence, add pre-commit tests for both, in
preparation to fix the issue in LoopAccessAnalysis.