This will result in larger atomic operations getting expanded to
`__atomic_*` libcalls via AtomicExpandPass, which matches what Clang
already does in the frontend.

Additionally, adjust some comments, and remove partial code dealing with
larger-than-128bit atomics, as it's now unreachable.

AArch64 always supports 128-bit atomics, so there's no conditionals
needed here. (Though: we really ought to require that a 128-bit load is
available, not just a cmpxchg, which would mean conditioning on LSE2.
But that's future work.)

The arm64-irtranslator.ll test was adjusted as it was using an i258 type
as a hack to avoid IR atomic lowering to test GlobalISel behavior. Pass
-mattr=+lse and use i32, instead, to accomplish that goal in a way that
continues to work.

The newly introduced LocationListLookupTestCase.test_loclist_expr test
fails with older clangs.

SimpleMachOHeaderMU can be used as a convenient base for classes that create
custom MachO headers. Instances of these custom classes can be used by passing
a MachOHeaderMUBuilder using the MachOPlatform extensions added in ef314d39.

Support was added for the following fusions:
  auipc-addi, slli-srli, ld-add
Some parts of the code became repetative, so small refactoring of
existing lui-addi fusion was done.

Reverting a workaround intended specifically for SPRI-V. That workaround
emerged from this discussion:

  * https://github.com/llvm/llvm-project/pull/72105

AFAIK, it hasn't been required in practice. This is based on IREE
(https://github.com/openxla/iree), which has just bumped it's fork of
LLVM without using it (*).

(*) https://github.com/openxla/iree/commit/cef31e775e03ec83420e4a7b47a992242d8df37c

This reverts commit bbd2b08b.

Clang's support for atomic operations on long doubles is currently broken,
so these tests don't work everywhere. This is a long standing condition and
the goal of this patch is to get the CI green again on all platforms.

The actual Clang fixes will be pursued separately.

Fixes #73791

For a character literal that is split over more than one source line
with free form line continuation using '&'
at the end of one line but missing the standard-required '&' on the
continuation line, also handle the case of spaces at the beginning of
the continuation line.
    
For example,
    
PRINT *, 'don'&
   't poke the bear'
    
now prints "don't poke the bear", like nearly all other Fortran
compilers do.
    
This is not strictly standard conforming behavior, and the compiler
emits a portability warning with -pedantic.
    
Fixes llvm-test-suite/Fortran/gfortran/regression/continuation_1.f90,
.../continuation_12.f90, and .../continuation_13.f90.

There was some confusion about units (bytes vs characters) in the
handling of the amount of input remaining in fixed-width formatted input
fields. Clarify that any variable or parameter counting "remaining"
space in a field in the I/O runtime is always in units of bytes, and
make it so where it wasn't.

Fixes the bug(s) in
llvm-test-suite/Fortran/gfortran/regression/char4_iunit_2.f03, although
the test still won't pass due to its dependence on gfortran's
list-directed output spacing.

The overflow check didn't work for a 27-digit octal field containing an
80-bit x87 extended precision real value. The count of bytes required
was too large because the leading digit (1) was assumed to require a
full three bits. And the actual transmission of the octal input digits
to the output buffer was incorrect, too.

Fixes llvm-test-suite/Fortran/gfortran/regression/boz_15.f90.

Most Fortran implementations support a READ statement after a WRITE
without repositioning on a sequential unit; it implies on ENDFILE and
then hits an EOF condition.

Fixes llvm-test-suite/Fortran/gfortran/regression/backspace_2.f.

This patch fixes:

  bolt/lib/Core/BinaryFunctionProfile.cpp:222:10: error: variable
  'BBMergeSI' set but not used [-Werror,-Wunused-but-set-variable]

  bolt/lib/Passes/VeneerElimination.cpp:67:12: error: variable
  'VeneerCallers' set but not used [-Werror,-Wunused-but-set-variable]

This makes it consistent with other builtins that require a specific
extension.

The "to be enabled" seemed unnecessary.

… input

The current EOF detection method (IsAtEOF()) depends on comparing the
current record number with the record number of the endfile record, if
it is known, which it is for units that have been written and then
rewound for input. For formatted input, this is wrong in the case of a
unit written with in-band newline characters. Rather than scan output
data to count newlines, it's best to just organically determine EOF by
detecting a failed or short read(), as we would have done anyway had the
endfile record number not been known. (I considered resetting the
endfile record number at the point of a REWIND, but not all rewinds are
followed by input; it seems wiser to defer the resetting until an actual
READ takes place.)

Fixes llvm-test-suite/Fortran/gfortran/regression/backslash_2.f90

Lowering doesn't use it, and won't need it in the future; it emits
in-line code for conversions and for assignments to scalars, and uses
the general Assign() routine for arrays.

…was written

At the end of an internal output statement, The I/O runtime fills (the
remainder of) the current record with blanks if it's the only record or
if anything had been written to it. This turns out to be wrong in the
case of a format that ends with an explicit advance to the next record,
which needs to be cleared even if nothing has been written.

Fixes llvm-test-suite/Fortran/gfortran/regression/arrayio_1.f90.

Provide backwards compatibility for YAML profile that uses `std::hash`:
xxh3 hash is the default for newly produced profile (sets `std-hash:
false`),
whereas the profile that doesn't specify `std-hash` will be treated as
`std-hash: true`, preserving old behavior.

After a non-advancing WRITE to a unit, ensure that any ENDFILE operation
(explicit or implicit) terminates the record. (All other Fortran
implementations do so except XLF.)

Fixes llvm-test-suite/Fortran/gfortran/regression/advance_6.f90.

We only need to check the result type. Use getBuiltinVectorTypeInfo
to lookup the element size.

This is an extension to the protocol that emits the declaration
information along with the metadata of each variable. This can be used
by vscode extensions to implement, for example, a "goToDefinition"
action in the debug tab, or for showing the value of a variable right
next to where it's declared during a debug session.
As this is cheap, I'm not gating this information under any setting.

A tricky case in Fw.d output editing is when the value needs to be
rounded either to a signed zero or away from zero to a power of ten
(1.0, 0.1, &c.). A bug report for LLVM on GitHub (#74274) exposed a bug
in this code in the case of Fw.0 editing where a value just over 0.5 was
rounded incorrectly to 0 rather than 1 when no fractional digits were
requested.

Rework that algorithm a little, ensuring that the initial
binary->decimal conversion produces at least one digit, and coping
correctly with the rounding of an exact 0.5 value for Fw.0 editing
(rounding it to the nearest even decimal, namely 0, following
near-universal compiler-dependent behavior in other Fortrans).

Fixes https://github.com/llvm/llvm-project/issues/74274.

sm_80 only has f32->bf16 conversions, the remaining integer conversions
arrived with sm_90. Use a two-step conversion for sm_80.

There doesn't seem to be a way to express this promotion directly within
the legalization framework, so fallback on Custom lowering.

An INTENT(IN) attribute on a pointer dummy argument prevents
modification of the pointer itself only, not modification of any
component of its target. Fix this case without breaking definability
checking for pointer components of non-pointer INTENT(IN) dummy
arguments.

The present implementation of defined formatted I/O is incorrect for
arrays in the data item list; it assumes that a DT defined format
descriptor (or list-directed/namelist instance) applies to all of the
elements in the array. The loop over the elements in the array is within
the DefinedFormattedIo() template function that handles defined
formatted I/O, not around its calls. This causes only one format list
edit descriptor to be used for the whole array, which is of course
wrong.

Invert this arrangment by performing the per-element looping in at the
top level in FormattedDerivedTypeIo() instead.

Defined unformatted I/O remains as it was.

Allow C-API users to debug their JITed code via the GDB JIT Interface.

This is currently supported on ELF and MachO based platforms. On
other systems `LLVMOrcLLJITEnableDebugSupport()` returns an error.

This patch adds a new C-API header `LLJITUtils.h`, which can host
further advanced JIT features in the future. Using the header requires
linking against LLVMOrcDebugging.

Currently there's an include in which `[opt]` might be emitted twice if
the frame format also asks for it. As a trivial fix, we should manually
emit `[opt]` only if a custom frame format is not specified.

Defined unformatted I/O is not allowed except from/to an external unit.
This restriction prohibits an INQUIRE(IOLENGTH=n) statement from using
derived types with defined unformatted output in its I/O list. The
runtime currently detects this case and crashes with an internal error;
this patch defines a new I/O error enum and causes the program to crash
with a more useful message.

Neoverse N2 was incorrectly marked as an Armv8.5a core. This has been
changed to an Armv9.0a core. However, crypto options are not enabled
by default for Armv9 cores, so -mcpu=neoverse-n2+crypto is required
to enable crypto for this core.

Neoverse N2 Technical Reference Manual:
   https://developer.arm.com/documentation/102099/0003/

An unsigned integer was being initialized with -1 to set all its bits to
1, but this doesn't work for the BigInt class which may be used as an
integer type on systems that don't support uint128 natively. This patch
moves the initialization to use ~T(0) instead.

no_unique_address makes it possible for a class to be empty and have
non-zero virtual size, so just remove this assert.

Bug: https://github.com/llvm/llvm-project/issues/74442