Summary:
The previous offloading entry type did not fit the current use-cases
very well. This widens it and adds a version to prevent further
annoyances. It also includes the kind to better sort who's using it.

The first 64-bytes are reserved as zero so the OpenMP runtime can detect
the old format for binary compatibilitry.

Summary:
This patch reworks how we handle global constructors in OpenMP.
Previously, we emitted individual kernels that were all registered and
called individually. In order to provide more generic support, this
patch moves all handling of this to the target backend and the runtime
plugin. This has the benefit of supporting the GNU extensions for
constructors an destructors, removing a class of failures related to
shared library destruction order, and allows targets other than OpenMP
to use the same support without needing to change the frontend.

This is primarily done by calling kernels that the backend emits to
iterate a list of ctor / dtor functions. For x64, this is automatic and
we get it for free with the standard `dlopen` handling. For AMDGPU, we
emit `amdgcn.device.init` and `amdgcn.device.fini` functions which
handle everything atuomatically and simply need to be called. For NVPTX,
a patch https://github.com/llvm/llvm-project/pull/71549 provides the
kernels to call, but the runtime needs to set up the array manually by
pulling out all the known constructor / destructor functions.

One concession that this patch requires is the change that for GPU
targets in OpenMP offloading we will use `llvm.global_dtors` instead of
using `atexit`. This is because `atexit` is a separate runtime function
that does not mesh well with the handling we're trying to do here. This
should be equivalent in all cases except for cases where we would need
to destruct manually such as:

```
struct S { ~S() { foo(); } };
void foo() {
  static S s;
}
```

However this is broken in many other ways on the GPU, so it is not
regressing any support, simply increasing the scope of what we can
handle.

This changes the handling of ctors / dtors. This patch now outputs a
information message regarding the deprecation if the old format is used.
This will be completely removed in a later release.

Depends on: https://github.com/llvm/llvm-project/pull/71549

The KernelEnvironment is for compile time information about a kernel. It
allows the compiler to feed information to the runtime. The
KernelLaunchEnvironment is for dynamic information *per* kernel launch.
It allows the rutime to feed information to the kernel that is not
shared with other invocations of the kernel. The first use case is to
replace the globals that synchronize teams reductions with per-launch
versions. This allows concurrent teams reductions. More uses cases will
follow, e.g., per launch memory pools.

Fixes: https://github.com/llvm/llvm-project/issues/70249

Summary:
A previous patch changed the logic to force external visibliity on
declare target variables. This is because they need to be exported in
the dynamic symbol table to be usable as the standard depicts. However,
the logic was always setting the visibility to `protected`, which would
override some symbols. For example, when calling `libc` functions for
CPU offloading. This patch changes the logic to only fire if the
variable has hidden visibliity to start with.

Summary:
There's some logic in the AMDGPU target that manually resets the
requested visibility of certain variables. This was triggering when we
set a constant variable in OpenMP. However, we shouldn't do this for
OpenMP when the variable has the `nohost` type. That implies that the
variable is not visible to the host and therefore does not need to be
visible, so we should respect the original value of it.

Currently, the precense of the OpenMP target declare metadata requires
that we always codegen a global declaration. This is undesirable in the
case that we could defer or omit this declaration as is common with
unused extern variables. This is important as it allows us, in the
runtime, to rely on static linking semantics to omit unused symbols so
they are not included when the user links it in.

This patch changes the check for always emitting these variables.
Because of this we also need to extend this logic to the generation of
the offloading entries. This has the result of derring the offload entry
generation to the canonical definitoin. So we are effectively assuming
whoever owns the storage for this variable will perform that operation.
This makes an exception for `link` attributes as those require their own
special handling.

Let me know if this is sound in the implementation, I do not have the
largest view of the standards here.

Fixes: https://github.com/llvm/llvm-project/issues/64133

Reviewed By: tianshilei1992

Differential Revision: https://reviews.llvm.org/D156368

This patch renames the `OpenMPIRBuilderConfig` flags to reduce confusion over
their meaning. `IsTargetCodegen` becomes `IsGPU`, whereas `IsEmbedded` becomes
`IsTargetDevice`. The `-fopenmp-is-device` compiler option is also renamed to
`-fopenmp-is-target-device` and the `omp.is_device` MLIR attribute is renamed
to `omp.is_target_device`. Getters and setters of all these renamed properties
are also updated accordingly. Many unit tests have been updated to use the new
names, but an alias for the `-fopenmp-is-device` option is created so that
external programs do not stop working after the name change.

`IsGPU` is set when the target triple is AMDGCN or NVIDIA PTX, and it is only
valid if `IsTargetDevice` is specified as well. `IsTargetDevice` is set by the
`-fopenmp-is-target-device` compiler frontend option, which is only added to
the OpenMP device invocation for offloading-enabled programs.

Differential Revision: https://reviews.llvm.org/D154591

This patch changes the handling of OpenMP to add the device attributes
to the canonical definitions when we encounter a non-canonical
definition. Previously, the following code would not work because it
would find the non-canonical definition first which would then not be
used anywhere else.

```
int x;
extern int x;
```

This patch now adds the attribute to both of them. This allows us to
perform the following operation if, for example, there were an
implementation of `stderr` on the device.

```
#include <stdio.h>

// List of libc symbols supported on the device.
extern FILE *stderr;
```

Unfortunately I cannot think of an equivalent solution to HIP / CUDA
device declarations as those are done with simple attributes. Attributes
themselves cannot be used to affect a definition once its canonical
definition has already been seen. Some help on that front would be
appreciated.

Fixes https://github.com/llvm/llvm-project/issues/63355

Reviewed By: ABataev

Differential Revision: https://reviews.llvm.org/D153369

Re-apply of: 3d0e9edd8e53fb72e85084f4170513159212839a
Reverted in: 0cb65b0a585c8b3d4a8a2aefe994a8fc907934f8

A function parameter was using the wrong type 'llvm::TargetRegion' instead of
'const llvm:: TargetRegion&', which caused the error in the address sanitizer.
The correct type is now used.

This patch puts the individual target region information attributes into a
struct so that the nested mappings are not needed and passing the information
around is simplified.

Reviewed By: jdoerfert, mikerice

Differential Revision: https://reviews.llvm.org/D136601