Add `dead_on_return` attribute, which is meant to be taken advantage
by the frontend, and states that the memory pointed to by the argument
is dead upon function return. As with `byval`, it is supposed to be
used for passing aggregates by value. The difference lies in the ABI:
`byval` implies that the pointer is explicitly passed as argument to
the callee (during codegen the copy is emitted as per byval contract),
whereas a `dead_on_return`-marked argument implies that the copy
already exists in the IR, is located at a specific stack offset within
the caller, and this memory will not be read further by the caller upon
callee return – or otherwise poison, if read before being written.

RFC: https://discourse.llvm.org/t/rfc-add-dead-on-return-attribute/86871.

CodeExtractor can currently erroneously insert an alloca into a
different function than it inserts its users into, in cases where code
is being extracted out of a function that has already been outlined. Add
an assertion that the two blocks being inserted into are actually in the
same function.

Add a check to findAllocaInsertPoint in OpenMP to LLVMIR translation to
prevent the aforementioned scenario from happening.

OpenMPIRBuilder relies on a callback mechanism to fix-up a module later
on during the finaliser step. In some cases this results in the module
being invalid prior to the finalise step running. Remove calls to
verifyModule wrapped in LLVM_DEBUG from CodeExtractor, as the presence
of those results in the compiler crashing with -mllvm -debug due to
premature module verification where it would not crash without -debug.

Call ompBuilder->finalize() the end of mlir::translateModuleToLLVMIR, in
order to make sure the module has actually been finalized prior to
trying to verify it.

Resolves https://github.com/llvm/llvm-project/issues/138102.

---------

Signed-off-by: Kajetan Puchalski <kajetan.puchalski@arm.com>

Seeing how we can't generate any debug intrinsics any more: delete a
variety of codepaths where they're handled. For the most part these are
plain deletions, in others I've tweaked comments to remain coherent, or
added a type to (what was) type-generic-lambdas.

This isn't all the DbgInfoIntrinsic call sites but it's most of the
simple scenarios.

Co-authored-by: Nikita Popov <github@npopov.com>

This flag was used to let us incrementally introduce debug records
into LLVM, however everything is now using records. It serves no
purpose now, so delete it.

If we use `CodeExtractor` to extract the block1 into a new function,

```
define void @foo() !dbg !2 {
entry:
  %1 = alloca i32, i64 1, align 4
  %2 = alloca i32, i64 1, align 4
  #dbg_declare(ptr %1, !8, !DIExpression(), !1)
  br label %block1

block1:
  store i32 1, ptr %1, align 4
  store i32 2, ptr %2, align 4
  #dbg_declare(ptr %2, !10, !DIExpression(), !1)
  ret void
}
```

it will look like the extracted function shown below (with some
irrelevent details removed).

```
define internal void @extracted(ptr %arg0, ptr %arg1) { 
newFuncRoot:
  br label %block1

block1:
  store i32 1, ptr %arg0, align 4
  store i32 2, ptr %arg1, align 4
  ret void
}
```

You will notice that it has replaced the usage of values that were in
the parent function (%1 and %2) with the arguments to the new function.
But it did not do the same thing with `#dbg_declare` which was simply
dropped because its location pointed to a value outside of the new
function. Similarly arg0 is without any debug record, although the value
that it replaced had one and we could materialize one for it based on
that.

This is not just a theoretical limitations. `CodeExtractor` is used to
create functions that implement many of the `OpenMP` constructs in
`OMPIRBuilder`. As a result of these limitations, the debug information
is missing from the created functions.

This PR tries to address this problem. It iterates over the input to the
extracted function and looks at their debug uses. If they were present
in the new function, it updates their location. Otherwise it materialize
a similar usage in the new function.

Most of these changes are localized in `fixupDebugInfoPostExtraction`.
Only other change is to propagate function inputs and the replacement
values to it.

---------

Co-authored-by: Tim Gymnich <tim@gymni.ch>
Co-authored-by: Michael Kruse <llvm-project@meinersbur.de>

Moving code to another function can lead to missed optimization
opportunities, because function passes operate on smaller chunks of
code, and they cannot figure out all details.

One example of missed optimization opportunities after code extraction
is information about pointer alignment. The instruction combine pass
adds information about pointer alignment to LLVM intrinsic memcpy calls
if it can deduce it from the code or if align metadata is added. If this
information is not present, then further optimization passes can
generate inefficient code.

If we add align metadata to extracted pointers, then the instruction
combine pass can add the align attribute to the LLVM intrinsic memcpy
call and unblock further optimization.

Scope of changes:
1. Analyze MLIR map operations. Add information about the alignment of
objects that are passed by reference to OpenMP GPU kernels.
2. Propagate alignment information to the outlined by `CodeExtractor`
helper functions.

musttail calls have several restrictions, generally enforcing matching
calling conventions between the caller parent and musttail callee. We
can't usually honor them, because the extracted function has a different
signature altogether, taking inputs/outputs and returning a control-flow
identifier rather than the actual return value.

Don't consider musttail calls as valid for extraction.

This PR removes the old `nocapture` attribute, replacing it with the new
`captures` attribute introduced in #116990. This change is
intended to be essentially NFC, replacing existing uses of `nocapture`
with `captures(none)` without adding any new analysis capabilities.
Making use of non-`none` values is left for a followup.

Some notes:
* `nocapture` will be upgraded to `captures(none)` by the bitcode
   reader.
* `nocapture` will also be upgraded by the textual IR reader. This is to
   make it easier to use old IR files and somewhat reduce the test churn in
   this PR.
* Helper APIs like `doesNotCapture()` will check for `captures(none)`.
* MLIR import will convert `captures(none)` into an `llvm.nocapture`
   attribute. The representation in the LLVM IR dialect should be updated
   separately.