Generate nuw GEPs for struct member accesses, as inbounds + non-negative
implies nuw.

Regression tests are updated using update scripts where possible, and by
find + replace where not.

IR for 'target teams loop' is now dependent on suitability of associated
loop-nest.

If a loop-nest:

- does not contain a function call, or
- the -fopenmp-assume-no-nested-parallelism has been specified,
- or the call is to an OpenMP API AND
- does not contain nested loop bind(parallel) directives

then it can be emitted as 'target teams distribute parallel for', which
is the current default. Otherwise, it is emitted as 'target teams
distribute'.

Added debug output indicating how 'target teams loop' was emitted. Flag
is -mllvm -debug-only=target-teams-loop-codegen

Added LIT tests explicitly verifying 'target teams loop' emitted as a
parallel loop and a distribute loop.

Updated other 'loop' related tests as needed to reflect change in IR.
- These updates account for most of the changed files and
additions/deletions.

A kernel implicit parameter (dyn_ptr) was introduced some time back.
This patch increments the kernel args version for a compiler supporting
dyn_ptr. The version will be used by the runtime to determine whether
the implicit parameter is generated by the compiler. The versioning is
required to support use cases where code generated by an older compiler
is linked with a newer runtime.

If approved, this patch should be backported to release 18.

Authored-by: Raúl Peñacoba Veigas <rpenacob@bsc.es>

Summary:
Currently, OpenMP handles the `omp requires` clause by emitting a global
constructor into the runtime for every translation unit that requires
it. However, this is not a great solution because it prevents us from
having a defined order in which the runtime is accessed and used.

This patch changes the approach to no longer use global constructors,
but to instead group the flag with the other offloading entires that we
already handle. This has the effect of still registering each flag per
requires TU, but now we have a single constructor that handles
everything.

This function removes support for the old `__tgt_register_requires` and
replaces it with a warning message. We just had a recent release, and
the OpenMP policy for the past four releases since we switched to LLVM
is that we do not provide strict backwards compatibility between major
LLVM releases now that the library is versioned. This means that a user
will need to recompile if they have an old binary that relied on
`register_requires` having the old behavior. It is important that we
actively deprecate this, as otherwise it would not solve the problem of
having no defined init and shutdown order for `libomptarget`. The
problem of `libomptarget` not having a define init and shutdown order
cascades into a lot of other issues so I have a strong incentive to be
rid of it.

It is worth noting that the current `__tgt_offload_entry` only has space
for a 32-bit integer here. I am planning to overhaul these at some point
as well.

We used to have two separate implementations to derive the number of
threads used in a target region. This lead us to sometimes miss out on
user provided thread bounds (num_threads, or thread_limit) when we
looked for "constant default values". If we might miss out on the
presence of those bounds, we cannot set the thread_limit statically
since the runtime will try to honor user input rather than cap it at the
"preferred default". This patch replaces the secondary implementation
with the primary in a mode that will not emit code but just look for the
presence, and potentially upper bounds, of thread limiting clauses.

The runtime test would not pass without this rewrite as we missed some
clauses, set the static limit on the device to the preferred value, but
then violated that value at runtime.

Fixes: https://github.com/llvm/llvm-project/issues/64845

Differential Revision: https://reviews.llvm.org/D158381

The loop directive is a descriptive construct which allows the compiler
flexibility in how it generates code for the directive's associated
loop(s). See OpenMP specification 5.2 [257:8-9].

Codegen added in this patch for the combined 'loop' directives are:

'target teams loop'     -> 'target teams distribute parallel for'
'teams loop'            -> 'teams distribute parallel for'
'target parallel loop'  -> 'target parallel for'
'parallel loop'         -> 'parallel for'

NOTE: The implementation of the 'loop' directive itself is unchanged.

Differential Revision: https://reviews.llvm.org/D145823