Locate the assembler tools before checking for support for various
assembler features.

Instead of generating version.h, move the so version there and parse it
in meson.

On AArch64, the performance counter registers usually are
restricted and not accessible from user space.

On macOS, we currently use mach_absolute_time() as timer on
aarch64. This measures wallclock time but with a very coarse
resolution.

There is a private API, kperf, that one can use for getting
high precision timers though. Unfortunately, it requires running
the checkasm binary as root (e.g. with sudo).

Also, as it is a private, undocumented API, it can potentially
change at any time.

This is handled by adding a new meson build option, for switching
to this timer. If the timer source in checkasm could be changed
at runtime with an option, this wouldn't need to be a build time
option.

This allows getting benchmarks like this:

mc_8tap_regular_w16_hv_8bpc_c:              1522.1 ( 1.00x)
mc_8tap_regular_w16_hv_8bpc_neon:            331.8 ( 4.59x)

Instead of this:

mc_8tap_regular_w16_hv_8bpc_c:                 9.0 ( 1.00x)
mc_8tap_regular_w16_hv_8bpc_neon:              1.9 ( 4.76x)

Co-authored-by: J. Dekker <jdek@itanimul.li>

arm32: 2 byte alignment saves 136 bytes
arm64: 4 byte alignment saves 1200 bytes

First check if the assembler supports the ".arch" directive, and
what architecture levels are supported.

In principle, we'd only need to check for support for ".arch armv8.2-a",
since that's enough for enabling the i8mm and sve2 extensions.

However, recent Clang versions (before version 17) wasn't able to
enable the dotprod and i8mm extensions via the ".arch_extension"
directives, so check for support for armv8.4-a and armv8.6-a as well,
which enable dotprod and i8mm implicitly.

This allows assembling these instructions on most commonly available
GCC and Clang based toolchains, while still allowing toggling support
for the instruction sets on and off within the source files.

Within assembly, we disable these extensions by default, so that
instructions enabled within these extension sets can't be used
by accident in unintended functions. Code meaning to use these
extensions can be assembled like this:

    #if HAVE_SVE
    ENABLE_SVE
    // code
    DISABLE_SVE
    #endif

Support for '.option arch' directive [0] was added to binutils in
d3ffd7f77654adafe5f1989bdfdbe4a337ff2e8b [1] and in llvm in
9e8ed3403c191ab9c4903e8eeb8f732ff8a43cb4 [2].

[0] https://github.com/riscv-non-isa/riscv-asm-manual/pull/67
[1] https://sourceware.org/git/?p=binutils-gdb.git;a=commit;h=d3ffd7f77654adafe5f1989bdfdbe4a337ff2e8b
[2] https://github.com/llvm/llvm-project/commit/9e8ed3403c191ab9c4903e8eeb8f732ff8a43cb4

For now the only CPU flag we check for is RISC-V Vector extension (RVV).

All of them are 32 bits values that shall be > 0

Signed-off-by: James Almer <jamrial@gmail.com>

Nothing in the spec prevents a Temporal Unit from having more than one Metadata
OBU of type ITU-T T.35, so export them as an array instead of only exporting
the last one we parse.
This is backwards compatible with the previous implementation, as users unaware
of this change can ignore the n_itut_t35 field and still access the first (or
only) entry in the array as they have been doing until now.

James Almer authored 2 years ago and Jean-Baptiste Kempf committed 2 years ago

Nothing in the spec prevents a Temporal Unit from having more than one Metadata
OBU of type ITU-T T.35, so export them as an array instead of only exporting
the last one we parse.
This is backwards compatible with the previous implementation, as users unaware
of this change can ignore the n_itut_t35 field and still access the first (or
only) entry in the array as they have been doing until now.

Signed-off-by: James Almer <jamrial@gmail.com>

This fixes a regression from 7409a189

"From VideoLAN with love"

Add an option for selecting the core where the single thread of
checkasm runs. This allows benchmarking on specific CPU cores on
heterogenous CPUs, like ARM big.LITTLE configurations.

On Linux, one can easily wrap an invocation of checkasm with
"taskset -c <n> [...]" - so this option isn't very essential
there - however it is quite useful on Windows.

On Windows, it is somewhat possible to do the same by launching
the tool with "start /B /affinity <hexmask> [...]", but that
doesn't work well with scripting ("start" returns before the
command has finished running, and it's not obvious how to
invoke "start" from within WSL).

Using "taskset" to launch processes on specific cores within WSL
on Windows doesn't work - regardless of the Linux level affinity,
the process ends up running on the performance cores anyway.

Henrik Gramner authored 2 years ago and Henrik Gramner committed 2 years ago

The intent was good, but in practice it results in a significant
amount of problems due to various compiler bugs for negligible gains.

Should be useful for scenarios like wanting only keyframes to quickly generate
a set of preview images of the whole stream.

Already implied when -D_POSIX_C_SOURCE is not passed.

Non-GNU systems enable extensions (XSI, BSD, GNU) by default.

Despite not being documented in Meson's list of canonical system names,
Meson does accept 'ios' mostly a synonym for darwin.

By using 'ios' instead of darwin, it allows distinguishing between the
two in the cases where that is necessary. Therefore, within dav1d, allow
using the 'ios' name as alias for 'darwin' for system name, to allow
using cross files that does this distinction.

meson itself also allows 'tvos' in addition to 'ios' in the internal
`is_darwin()` function, as such all 3 are handled the same here.

Henrik Gramner authored 2 years ago and Henrik Gramner committed 2 years ago

Whitespace is added to the result if compiling with MSVC using /std:c11
which breaks various things. Adding strip() fixes the problem.

Henrik Gramner authored 2 years ago and Henrik Gramner committed 2 years ago

Use explicit parameter type detection and manually clobber the
upper bits instead of relying on internal compiler behavior.

Since meson 0.58.0 (released in May 2021), meson accepts adding '.S'
assembly files as source files to the clang-cl compiler.

If using an older version of meson, keep using gas-preprocessor
just like for MSVC builds.