Fold icmp between a chain of geps and its base pointer. Previously only
a single gep was supported.
    
This will be extended to handle the case of two gep chains with a common
base in a followup.

This helps to avoid regressions after #137297.

Load the nowrap flags before calling EmitGEPOffset(), as this may
free the instruction.

We already do this when both sides are a GEP, but not if only one is.
This ensures that the offset arithmetic is not duplicated.

Co-authored-by: Yingwei Zheng <dtcxzyw2333@gmail.com>

Closes #143211.

Having a finite Depth (or recursion limit) for computeKnownBits is very
limiting, but is currently a load-bearing necessity, as all KnownBits
are recomputed on each call and there is no caching. As a prerequisite
for an effort to remove the recursion limit altogether, either using a
clever caching technique, or writing a easily-invalidable KnownBits
analysis, make the Depth argument in APIs in ValueTracking uniformly the
last argument with a default value. This would aid in removing the
argument when the time comes, as many callers that currently pass 0
explicitly are now updated to omit the argument altogether.

icmp ne X, (sext (icmp ne X, 0)) --> X != 0 && X != -1, not X != 0 && X
== -1, which would go to X == -1 anyway.

Match icmps of binops where both operands are select with constant arms,
i.e., `icmp pred (select A ? C1 : C2) binop (select B ? C3 : C4), C5`.
Fold such patterns by creating a truth table of the possible four
constant variants, and materialize back the optimal logic from it via
`createLogicFromTable` helper. This also generalizes an existing fold,
which has therefore been dropped.

Proofs: https://alive2.llvm.org/ce/z/NS7Vzu.

Fixes: https://github.com/llvm/llvm-project/issues/138212.

Proof: https://alive2.llvm.org/ce/z/zQ2UW4
Closes https://github.com/llvm/llvm-project/issues/134024