This patch is split off from #81659, and contains just the Sema
infrastructure that we can later use to implement semantic analysis of
OpenACC constructs.

This reverts commit 2d616ec4.

Buildbot failures:
https://lab.llvm.org/buildbot/#/builders/177/builds/29364

This is a follow-up to 630548a1, which fixed builtbot failure https://lab.llvm.org/buildbot/#/builders/188/builds/41930

This is followup to https://github.com/llvm/llvm-project/pull/8120.
Missed a destuctor.

Currently the address reported by binutils for a global is its index;
but its offset (in the file or section) is more useful for binary size
attribution.
This PR treats globals similarly to functions, and tracks their offset
and size. It also centralizes the logic differentiating linked from object
and dylib files (where section addresses are 0).

Reverts llvm/llvm-project#81835
This is breaking arm32 which does not support 64 bit types.

[TargetLowering] Emit SIGN_EXTEND_INREG instead of shift pair from optimizeSetCCOfSignedTruncationCheck. (#81785)

sext_inreg is our canonical form of shift pair before op legalization so
DAG combiner will probably create it anyway. If it isn't legal
LegalizeDAG will expand to shifts later.

See discussion at
https://discourse.llvm.org/t/rfc-support-function-attributes-in-user-interface/76624

Demo macro:
```c++
#if !defined(__LIBC_CONST_ATTR) && defined(__cplusplus) && defined(__GNUC__)
#if __has_attribute(const)
#define __LIBC_CONST_ATTR [[gnu::const]]
#endif
#endif
#if !defined(__LIBC_CONST_ATTR) && defined(__GNUC__)
#if __has_attribute(const)
#define __LIBC_CONST_ATTR __attribute__((const))
#endif
#endif
#if !defined(__LIBC_CONST_ATTR)
#define __LIBC_CONST_ATTR
#endif
```

We used to emit dummy pointers for unknown declarations in certain
cases in C, but this is also necessary in C++.

I'm limiting this to static local variables for now.

This patch cleans up functions for checking inline literals.

This is a Global ISel equivalent of #80641, creating fneg(movi) instead
of the alternative constant pool load or gpr dup.

This patch introduces the new MPI dialect into MLIR. The Message Passing
Interface (MPI) is a widely-used standard for distributed programs to
exchange data. This PR goes together with a talk later at today's LLVM
Dev Meeting.

This is just a first, small patch to get going and add the necessary
base files, so that we can add more operations in further patches.

Here's the documentation as generated by `ninja mlir-doc`:
# 'mpi' Dialect

This dialect models the Message Passing Interface (MPI), version 
4.0. It is meant to serve as an interfacing dialect that is targeted
by higher-level dialects. The MPI dialect itself can be lowered to 
multiple MPI implementations and hide differences in ABI. The dialect
models the functions of the MPI specification as close to 1:1 as
possible
while preserving SSA value semantics where it makes sense, and uses 
`memref` types instead of bare pointers.

This dialect is under active development, and while stability is an
eventual goal, it is not guaranteed at this juncture. Given the early 
state, it is recommended to inquire further prior to using this dialect.

For an in-depth documentation of the MPI library interface, please refer
to official documentation such as the 
[OpenMPI online documentation](https://www.open-mpi.org/doc/current/).

[TOC]

## Operation definition

### `mpi.comm_rank` (mpi::CommRankOp)

_Get the current rank, equivalent to `MPI_Comm_rank(MPI_COMM_WORLD,
&rank)`_


Syntax:

```
operation ::= `mpi.comm_rank` attr-dict `:` type(results)
```

Communicators other than `MPI_COMM_WORLD` are not supported for now.

This operation can optionally return an `!mpi.retval` value that can be
used
to check for errors.

#### Results:

| Result | Description |
| :----: | ----------- |
| `retval` | MPI function call return value
| `rank` | 32-bit signless integer


### `mpi.error_class` (mpi::ErrorClassOp)

_Get the error class from an error code, equivalent to the
`MPI_Error_class` function_


Syntax:

```
operation ::= `mpi.error_class` $val attr-dict `:` type($val)
```

`MPI_Error_class` maps return values from MPI calls to a set of
well-known
MPI error classes.

#### Operands:

| Operand | Description |
| :-----: | ----------- |
| `val` | MPI function call return value

#### Results:

| Result | Description |
| :----: | ----------- |
| `errclass` | MPI function call return value


### `mpi.finalize` (mpi::FinalizeOp)

_Finalize the MPI library, equivalent to `MPI_Finalize()`_


Syntax:

```
operation ::= `mpi.finalize` attr-dict (`:` type($retval)^)?
```

This function cleans up the MPI state. Afterwards, no MPI methods may 
be invoked (excpet for MPI_Get_version, MPI_Initialized, and
MPI_Finalized).
Notably, MPI_Init cannot be called again in the same program.

This operation can optionally return an `!mpi.retval` value that can be
used
to check for errors.

#### Results:

| Result | Description |
| :----: | ----------- |
| `retval` | MPI function call return value


### `mpi.init` (mpi::InitOp)

_Initialize the MPI library, equivalent to `MPI_Init(NULL, NULL)`_


Syntax:

```
operation ::= `mpi.init` attr-dict (`:` type($retval)^)?
```

This operation must preceed most MPI calls (except for very few
exceptions,
please consult with the MPI specification on these).

Passing &argc, &argv is not supported currently.

This operation can optionally return an `!mpi.retval` value that can be
used
to check for errors.

#### Results:

| Result | Description |
| :----: | ----------- |
| `retval` | MPI function call return value


### `mpi.recv` (mpi::RecvOp)

_Equivalent to `MPI_Recv(ptr, size, dtype, dest, tag, MPI_COMM_WORLD,
MPI_STATUS_IGNORE)`_


Syntax:

```
operation ::= `mpi.recv` `(` $ref `,` $tag `,` $rank `)` attr-dict `:` type($ref) `,` type($tag) `,` type($rank)(`->` type($retval)^)?
```

MPI_Recv performs a blocking receive of `size` elements of type `dtype` 
from rank `dest`. The `tag` value and communicator enables the library
to
determine the matching of multiple sends and receives between the same 
ranks.

Communicators other than `MPI_COMM_WORLD` are not supprted for now.
The MPI_Status is set to `MPI_STATUS_IGNORE`, as the status object 
is not yet ported to MLIR.

This operation can optionally return an `!mpi.retval` value that can be
used
to check for errors.

#### Operands:

| Operand | Description |
| :-----: | ----------- |
| `ref` | memref of any type values
| `tag` | 32-bit signless integer
| `rank` | 32-bit signless integer

#### Results:

| Result | Description |
| :----: | ----------- |
| `retval` | MPI function call return value


### `mpi.retval_check` (mpi::RetvalCheckOp)

_Check an MPI return value against an error class_


Syntax:

```
operation ::= `mpi.retval_check` $val `=` $errclass attr-dict `:` type($res)
```

This operation compares MPI status codes to known error class
constants such as `MPI_SUCCESS`, or `MPI_ERR_COMM`.

#### Attributes:

<table>
<tr><th>Attribute</th><th>MLIR Type</th><th>Description</th></tr>

<tr><td><code>errclass</code></td><td>::mlir::mpi::MPI_ErrorClassEnumAttr</td><td><details><summary>MPI
error class name</summary>{{% markdown %}}Enum cases:
* MPI_SUCCESS (`MPI_SUCCESS`)
* MPI_ERR_ACCESS (`MPI_ERR_ACCESS`)
* MPI_ERR_AMODE (`MPI_ERR_AMODE`)
* MPI_ERR_ARG (`MPI_ERR_ARG`)
* MPI_ERR_ASSERT (`MPI_ERR_ASSERT`)
* MPI_ERR_BAD_FILE (`MPI_ERR_BAD_FILE`)
* MPI_ERR_BASE (`MPI_ERR_BASE`)
* MPI_ERR_BUFFER (`MPI_ERR_BUFFER`)
* MPI_ERR_COMM (`MPI_ERR_COMM`)
* MPI_ERR_CONVERSION (`MPI_ERR_CONVERSION`)
* MPI_ERR_COUNT (`MPI_ERR_COUNT`)
* MPI_ERR_DIMS (`MPI_ERR_DIMS`)
* MPI_ERR_DISP (`MPI_ERR_DISP`)
* MPI_ERR_DUP_DATAREP (`MPI_ERR_DUP_DATAREP`)
* MPI_ERR_ERRHANDLER (`MPI_ERR_ERRHANDLER`)
* MPI_ERR_FILE (`MPI_ERR_FILE`)
* MPI_ERR_FILE_EXISTS (`MPI_ERR_FILE_EXISTS`)
* MPI_ERR_FILE_IN_USE (`MPI_ERR_FILE_IN_USE`)
* MPI_ERR_GROUP (`MPI_ERR_GROUP`)
* MPI_ERR_INFO (`MPI_ERR_INFO`)
* MPI_ERR_INFO_KEY (`MPI_ERR_INFO_KEY`)
* MPI_ERR_INFO_NOKEY (`MPI_ERR_INFO_NOKEY`)
* MPI_ERR_INFO_VALUE (`MPI_ERR_INFO_VALUE`)
* MPI_ERR_IN_STATUS (`MPI_ERR_IN_STATUS`)
* MPI_ERR_INTERN (`MPI_ERR_INTERN`)
* MPI_ERR_IO (`MPI_ERR_IO`)
* MPI_ERR_KEYVAL (`MPI_ERR_KEYVAL`)
* MPI_ERR_LOCKTYPE (`MPI_ERR_LOCKTYPE`)
* MPI_ERR_NAME (`MPI_ERR_NAME`)
* MPI_ERR_NO_MEM (`MPI_ERR_NO_MEM`)
* MPI_ERR_NO_SPACE (`MPI_ERR_NO_SPACE`)
* MPI_ERR_NO_SUCH_FILE (`MPI_ERR_NO_SUCH_FILE`)
* MPI_ERR_NOT_SAME (`MPI_ERR_NOT_SAME`)
* MPI_ERR_OP (`MPI_ERR_OP`)
* MPI_ERR_OTHER (`MPI_ERR_OTHER`)
* MPI_ERR_PENDING (`MPI_ERR_PENDING`)
* MPI_ERR_PORT (`MPI_ERR_PORT`)
* MPI_ERR_PROC_ABORTED (`MPI_ERR_PROC_ABORTED`)
* MPI_ERR_QUOTA (`MPI_ERR_QUOTA`)
* MPI_ERR_RANK (`MPI_ERR_RANK`)
* MPI_ERR_READ_ONLY (`MPI_ERR_READ_ONLY`)
* MPI_ERR_REQUEST (`MPI_ERR_REQUEST`)
* MPI_ERR_RMA_ATTACH (`MPI_ERR_RMA_ATTACH`)
* MPI_ERR_RMA_CONFLICT (`MPI_ERR_RMA_CONFLICT`)
* MPI_ERR_RMA_FLAVOR (`MPI_ERR_RMA_FLAVOR`)
* MPI_ERR_RMA_RANGE (`MPI_ERR_RMA_RANGE`)
* MPI_ERR_RMA_SHARED (`MPI_ERR_RMA_SHARED`)
* MPI_ERR_RMA_SYNC (`MPI_ERR_RMA_SYNC`)
* MPI_ERR_ROOT (`MPI_ERR_ROOT`)
* MPI_ERR_SERVICE (`MPI_ERR_SERVICE`)
* MPI_ERR_SESSION (`MPI_ERR_SESSION`)
* MPI_ERR_SIZE (`MPI_ERR_SIZE`)
* MPI_ERR_SPAWN (`MPI_ERR_SPAWN`)
* MPI_ERR_TAG (`MPI_ERR_TAG`)
* MPI_ERR_TOPOLOGY (`MPI_ERR_TOPOLOGY`)
* MPI_ERR_TRUNCATE (`MPI_ERR_TRUNCATE`)
* MPI_ERR_TYPE (`MPI_ERR_TYPE`)
* MPI_ERR_UNKNOWN (`MPI_ERR_UNKNOWN`)
* MPI_ERR_UNSUPPORTED_DATAREP (`MPI_ERR_UNSUPPORTED_DATAREP`)
* MPI_ERR_UNSUPPORTED_OPERATION (`MPI_ERR_UNSUPPORTED_OPERATION`)
* MPI_ERR_VALUE_TOO_LARGE (`MPI_ERR_VALUE_TOO_LARGE`)
* MPI_ERR_WIN (`MPI_ERR_WIN`)
* MPI_ERR_LASTCODE (`MPI_ERR_LASTCODE`){{% /markdown
%}}</details></td></tr>
</table>

#### Operands:

| Operand | Description |
| :-----: | ----------- |
| `val` | MPI function call return value

#### Results:

| Result | Description |
| :----: | ----------- |
| `res` | 1-bit signless integer


### `mpi.send` (mpi::SendOp)

_Equivalent to `MPI_Send(ptr, size, dtype, dest, tag, MPI_COMM_WORLD)`_


Syntax:

```
operation ::= `mpi.send` `(` $ref `,` $tag `,` $rank `)` attr-dict `:` type($ref) `,` type($tag) `,` type($rank)(`->` type($retval)^)?
```

MPI_Send performs a blocking send of `size` elements of type `dtype` to
rank
`dest`. The `tag` value and communicator enables the library to
determine
the matching of multiple sends and receives between the same ranks.

Communicators other than `MPI_COMM_WORLD` are not supprted for now.

This operation can optionally return an `!mpi.retval` value that can be
used
to check for errors.

#### Operands:

| Operand | Description |
| :-----: | ----------- |
| `ref` | memref of any type values
| `tag` | 32-bit signless integer
| `rank` | 32-bit signless integer

#### Results:

| Result | Description |
| :----: | ----------- |
| `retval` | MPI function call return value


## Attribute definition

### MPI_ErrorClassEnumAttr

MPI error class name

Syntax:

```
#mpi.errclass<
  ::mlir::mpi::MPI_ErrorClassEnum   # value
>
```

Enum cases:
* MPI_SUCCESS (`MPI_SUCCESS`)
* MPI_ERR_ACCESS (`MPI_ERR_ACCESS`)
* MPI_ERR_AMODE (`MPI_ERR_AMODE`)
* ... *all other MPI error codes*

#### Parameters:

| Parameter | C++ type | Description |
| :-------: | :-------: | ----------- |
| value | `::mlir::mpi::MPI_ErrorClassEnum` | an enum of type
MPI_ErrorClassEnum |

## Type definition

### RetvalType

MPI function call return value

Syntax: `!mpi.retval`

This type represents a return value from an MPI function vall.
This value can be MPI_SUCCESS, MPI_ERR_IN_STATUS, or any error code.

This return value can be compared agains the known MPI error classes
represented by `#mpi.errclass` using the `mpi.retval_check` operation.

Extracing a subvector at index zero corresponds to a type conversion and
possibly a subregister operation. We will not emit a vslidedown. As
such, they are free.

As an aside, it looks like we're not passing an index in for cases where
the subvec type is scalable. For at least index zero, we probably should
be.

[clang] Allow builtin addc/subc to be constant evaluated

For wave64 WMMA instructions, putting W64 in the DecoderNamespace is
more descriptive than WMMA, and matches other uses for GFX12
GLOBAL_LOAD_TR instructions.

Teaching ConstantFoldLoadFromUniformValue that types that are padded in
memory can't be considered as uniform.

Using the big hammer to prevent optimizations when loading from a
constant for which DataLayout::typeSizeEqualsStoreSize would return
false.

Main problem solved would be something like this:
  store i17 -1, ptr %p, align 4
  %v = load i8, ptr %p, align 1
If for example the i17 occupies 32 bits in memory, then LLVM IR doesn't
really tell where the padding goes. And even if we assume that the 15
most significant bits are padding, then they should be considered as
undefined (even if LLVM backend typically would pad with zeroes).
Anyway, for a big-endian target the load would read those most
significant bits, which aren't guaranteed to be one's. So it would be
wrong to constant fold the load as returning -1.

If LLVM IR had been more explicit about the placement of padding, then
we could allow the consta...

First, we need to register local constant variables in C, so we get the
same diagnostic behavior as the current interpeter.

Second, when returning an LValue (as a Pointer), which we eventually
convert to an RValue, we need to do the conversion immediately when
saving the Pointer in the EvaluationResult. Otherwise, we will possibly
deallocate the data before doing the conversion (which will look at the
Block*).

The MSVC STL implementation declares multiple classes using:

```cpp
namespace std {
  extern "C++" class locale {
    ...
  };
}
```

`isInStdNamespace` uses the first DeclContext to check whether a Decl is
inside the `std` namespace. Here, the first DeclContext of the `locale`
Decl is a LinkageSpecDecl so the method will return false.
We need to skip this LinkageSpecDecl to find the first DeclContext of
type Namespace and actually check whether we're in the `std` namespace.

This is a reland of #81746

[libc][stdfix] Use __FRACT_FBIT__ for fixed point support detection instead of compiler version. (#81820)

Now that `__FRACT_FBIT__` and related macros are added in
https://github.com/llvm/llvm-project/pull/81207, it is safer to use them
for fixed point support detection, so that codes that do not use fixed
point types will not fail to build when `-ffixed-point` is missing.

This reverts commit 32fcfcdc.

In C++, alignas is an attribute specifier, while in C23, it's an alias
of _Alignas, which is a type specifier/qualifier. This means that they
parse differently in some circumstances.

Fixes https://github.com/llvm/llvm-project/issues/81472

This adds support for the AArch64 soft-float ABI. The specification for
this ABI was added by https://github.com/ARM-software/abi-aa/pull/232.

Because all existing AArch64 hardware has floating-point hardware, we
expect this to be a niche option, only used for embedded systems on
R-profile systems. We are going to document that SysV-like systems
should only ever use the base (hard-float) PCS variant:
https://github.com/ARM-software/abi-aa/pull/233. For that reason, I've
not added an option to select the ABI independently of the FPU hardware,
instead the new ABI is enabled iff the target architecture does not have
an FPU.

For testing, I have run this through an ABI fuzzer, but since this is
the first implementation it can only test for internal consistency
(callers and callees agree on the PCS), not for conformance to the ABI
spec.

Flang does not set the preprocessor define.