Most addresses in SystemZ instructions take two registers,
an index register and a base register.  However, either of
those can be omitted.  If there is just a single register,
this usually is taken as the base register - however, there
are certain rare cases where you specifically want to use
an index register but no base register.  This is currently
not handled consistently by the assembler / disassembler.

Fix this by
 - always emitting a dummy 0 as base register for index-
   only addresses
 - correctly handle dummy 0 as indicating no base register
   when parsing an address

This is compatible with current GNU binutils behavior.

The __builtin_s390_vceq* family of builtins currently take
signed arguments with clang, but unsigned with GCC.  Update
clang to match existing GCC precendent.

The builtins that expand to the vlrl/vlrlr and vstrl/vstrlr
instructions are currently named inconsistently between GCC
and clang.  Rename the clang versions to match GCC.

Clang currently implements a set of vector rotate builtins
(__builtin_s390_verll*) in terms of platform-specific LLVM
intrinsics.  To simplify the IR (and allow for common code
optimizations if applicable), this patch removes those LLVM
intrinsics and implements the builtins in terms of the
platform-independent funnel shift intrinsics instead.

Also, fix the prototype of the __builtin_s390_verll*
builtins for full compatibility with GCC.

This PR introduce `nvvm.fence.proxy` OP for the following cases:

```
nvvm.fence.proxy { kind = #nvvm.proxy_kind<alias>}
nvvm.fence.proxy { kind = #nvvm.proxy_kind<async>}
nvvm.fence.proxy { kind = #nvvm.proxy_kind<async.global>}
nvvm.fence.proxy { kind = #nvvm.proxy_kind<async.shared>, space = #nvvm.shared_space<cta>}
nvvm.fence.proxy { kind = #nvvm.proxy_kind<async.shared>, space = #nvvm.shared_space<cluster>}
```

GPU dialect has `#gpu.address_space<workgroup>` for shared memory of
NVGPU (address space =3). Howeverm when IR combine NVGPU and GPU
dialect, `nvgpu-to-nvvm` pass fails due to missing attribute conversion.

This PR adds `populateGpuMemorySpaceAttributeConversions` to
nvgou-to-nvvm lowering, so we can use `#gpu.address_space<workgroup>`
`nvgpu-to-nvvm` pass

MinBWs contains entries that specify the minimum required bitwidth. In
some cases, the old and new bitwidths can be equal (see test case) and
in those cases no truncations are needed, so skip those cases.

Fixes #74307.

We can use Intrinsic::getDeclaration() here, we just have to pass
the correct arguments. This function accepts only the mangled types,
not all argument types.

Enable by default for optimization levels higher than 0 (same behavior
as clang).

For simplicity, only forward the flag to the frontend driver when it
contradicts what is implied by the optimization level.

This was first landed in
https://github.com/llvm/llvm-project/pull/73111 but was later reverted
due to a performance regression. That regression was fixed by
https://github.com/llvm/llvm-project/pull/74065.

In preparation for running clang-format on the whole code base, we are
also removing mentions of the legacy _LIBCPP_INLINE_VISIBILITY macro in
favor of the newer _LIBCPP_HIDE_FROM_ABI.

We're still leaving the definition of _LIBCPP_INLINE_VISIBILITY to avoid
creating needless breakage in case some older patches are checked-in
with mentions of the old macro. After we branch for LLVM 18, we can do
another pass to clean up remaining uses of the macro that might have
gotten introduced by mistake (if any) and remove the macro itself at the
same time. This is just a minor convenience to smooth out the transition
as much as possible.

See
https://discourse.llvm.org/t/rfc-clang-formatting-all-of-libc-once-and-for-all
for the clang-format proposal.

Fix ppc build bot

This PR introduces DIGlobalVariableAttr and
DIGlobalVariableExpressionAttr so that ModuleTranslation can emit the
required metadata needed for debug information about global variable.
The translator implementation for debug metadata needed to be refactored
in order to allow translation of nodes based on MDNode
(DIGlobalVariableExpressionAttr and DIExpression) in addition to
DINode-based nodes.

A DIGlobalVariableExpressionAttr can now be passed to the GlobalOp
operation directly and ModuleTranslation will create the respective
DIGlobalVariable and DIGlobalVariableExpression nodes. The compile unit
that DIGlobalVariable is expected to be configured with will be updated
with the created DIGlobalVariableExpression.

Make a modernize version of abseil-string-find-startswith using the
available C++20 `std::string::starts_with` and
`std::string_view::starts_with`. Following up from
https://github.com/llvm/llvm-project/pull/72283.

This patch continues the work started with ea5b1ef0. See that commit and its corresponding PR for details.

This patch changes the bounds generation code shared between OpenMP and OpenACC to always attach an extent to the bounds generation. This is
currently required for OpenMP descriptor lowering but may not
necessarily be required in the case of OpenACC.

Split off live-in printing to VPlan::printLiveIns and use it to print
Live-ins when printing in the DOT format.

Check the operands of I are used in no more than one place, which can
not be deleted, cause a mul instruction has far more weight than add and
shl instruction in IR, thus this method cannot achieve the goal of
simplifying instructions, just return null.

Patch by: Kerry McLaughlin <kerry.mclaughlin@arm.com>

Clean up sve-tail-folding-option.ll by removing the unused
CHECK-TF-NEOVERSE-V1 prefix (note the use of non-opaque pointers) and
remove IR value references.

Merge consecutive AddrSpaceCasts into a single AddrSpaceCast.

1. COPYPRIVATE clause should be specified on END SINGLE construct.
2. NOWAIT clause should be specified on END DO/DO SIMD/SINGLE/SECTIONS
construct.

Special handling for semantic checks for nowait/copyprivate clause is
needed in Fortran due to the fact that Openmp pragmas for C/C++ doesn't
have end directive (clause). nowait/copyprivate clauses are allowed in
begin directive clause lists for C/C++ and it is not allowed for
Fortran.

Positive options: -mapx-features=<comma-separated-features>
Negative options: -mno-apx-features=<comma-separated-features>

-m[no-]apx-features is designed to be able to control separate APX
features.

Besides, we also support the flag -m[no-]apxf, which can be used like an
alias of -m[no-]apx-features=< all APX features covered by CPUID APX_F>

Behaviour when positive and negative options are used together:

For boolean flags, the last one wins

-mapxf   -mno-apxf   -> -mno-apxf
-mno-apxf   -mapxf   -> -mapxf

For flags that take a set as arguments, it sets the mask by order of the
flags

-mapx-features=egpr,ndd  -mno-apx-features=egpr  ->   -egpr,+ndd
-mapx-features=egpr  -mno-apx-features=egpr,ndd  ->   -egpr,-ndd
-mno-apx-features=egpr  -mapx-features=egpr,ndd  ->   +egpr,+ndd
-mno-apx-features=egpr,ndd  -mapx-features=egpr  ->   -ndd,+egpr

The design is aligned with gcc
https://gcc.gnu.org/pipermail/gcc-patches/2023-August/628905.html

Remove unused using declaration.

Extends the zero-vector test coverage in nontemporal-3.ll

We have a bunch of places where we have to guard against undef
to avoid multi-use issues, but would be fine with poison. Use a
different function for these to make it clear, and to indicate that
this check can be removed once we no longer support undef. I've
replaced some of the obvious cases, but there's probably more.

For now, the implementation is the same as UndefOrPoison, it just
has a more precise name.