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nix/src/libexpr/meson.build
Sergei Zimmerman 86a3fad085
libexpr: Improve lexer performance by using full scanner tables (-Cf)
This trades off some executable size for measurable lexer performance
improvements.

Note on the explicitly enabling 8bit scanner.
This is needed due to the default behavior of flex (excerpt from the manual [1]):

> Flex’s default behavior is to generate an 8-bit scanner unless you
> use the ‘-Cf’ or ‘-CF’, in which case flex defaults to generating
> 7-bit scanners unless your site was always configured to generate 8-bit
> scanners.

Some quantifyable metrics:

Nixpkgs revision: a6e3f45acf4e817532a861ab0eda4ab5485fecc1
Parsing the largest file in nixpkgs: pkgs/development/haskell-modules/hackage-packages.nix.

(Before this patch)

```
$ nix build github:nixos/nix/9fe3077d4#nix-expr
$ du --apparent-size result/lib/libnixexpr.so
2518    result/lib/libnixexpr.so
$ nix build github:nixos/nix/9fe3077d4#nix-cli
$ taskset -c 2,3 hyperfine "GC_INITIAL_HEAP_SIZE=16g \
    result/bin/nix-instantiate --parse               \
    ../nixpkgs/pkgs/development/haskell-modules/hackage-packages.nix > /dev/null"
  Time (mean ± σ):     375.5 ms ±   6.3 ms    [User: 316.9 ms, System: 56.7 ms]
  Range (min … max):   368.5 ms … 388.3 ms    10 runs
```

(After the patch)

```
$ nix build .#nix-expr
$ du --apparent-size result/lib/libnixexpr.so
2685    result/lib/libnixexpr.so
$ nix build .#nix-cli
$ taskset -c 2,3 hyperfine "GC_INITIAL_HEAP_SIZE=16g \
    result/bin/nix-instantiate --parse               \
    ../nixpkgs/pkgs/development/haskell-modules/hackage-packages.nix > /dev/null"
  Time (mean ± σ):     326.8 ms ±   4.9 ms    [User: 269.5 ms, System: 55.3 ms]
  Range (min … max):   319.7 ms … 335.5 ms    10 runs
```

Overall, the change is roughly:

- 2518KiB -> 2685KiB ~ 150 KiB of machine code
- 375ms -> 325ms ~ 50ms

The perf uplift for eval-heavy test cases is obviously less noticeable,
but it doesn't make sense not to take this free perf win.

[1]: https://westes.github.io/flex/manual/Options-Affecting-Scanner-Behavior.html#Options-Affecting-Scanner-Behavior
2025-05-01 23:10:04 +00:00

185 lines
4.2 KiB
Meson

project('nix-expr', 'cpp',
version : files('.version'),
default_options : [
'cpp_std=c++2a',
# TODO(Qyriad): increase the warning level
'warning_level=1',
'errorlogs=true', # Please print logs for tests that fail
],
meson_version : '>= 1.1',
license : 'LGPL-2.1-or-later',
)
cxx = meson.get_compiler('cpp')
subdir('nix-meson-build-support/deps-lists')
configdata_pub = configuration_data()
configdata_priv = configuration_data()
deps_private_maybe_subproject = [
]
deps_public_maybe_subproject = [
dependency('nix-util'),
dependency('nix-store'),
dependency('nix-fetchers'),
]
subdir('nix-meson-build-support/subprojects')
subdir('nix-meson-build-support/big-objs')
# Check for each of these functions, and create a define like `#define HAVE_LCHOWN 1`.
check_funcs = [
'sysconf',
]
foreach funcspec : check_funcs
define_name = 'HAVE_' + funcspec.underscorify().to_upper()
define_value = cxx.has_function(funcspec).to_int()
configdata_priv.set(define_name, define_value)
endforeach
boost = dependency(
'boost',
modules : ['container', 'context'],
include_type: 'system',
)
# boost is a public dependency, but not a pkg-config dependency unfortunately, so we
# put in `deps_other`.
deps_other += boost
nlohmann_json = dependency('nlohmann_json', version : '>= 3.9')
deps_public += nlohmann_json
bdw_gc = dependency('bdw-gc', required : get_option('gc'))
if bdw_gc.found()
deps_public += bdw_gc
foreach funcspec : [
'pthread_attr_get_np',
'pthread_getattr_np',
]
define_name = 'HAVE_' + funcspec.underscorify().to_upper()
define_value = cxx.has_function(funcspec).to_int()
configdata_priv.set(define_name, define_value)
endforeach
# Affects ABI, because it changes what bdw_gc itself does!
configdata_pub.set('GC_THREADS', 1)
endif
# Used in public header. Affects ABI!
configdata_pub.set('NIX_USE_BOEHMGC', bdw_gc.found().to_int())
toml11 = dependency(
'toml11',
version : '>=3.7.0',
method : 'cmake',
include_type: 'system',
)
deps_other += toml11
config_priv_h = configure_file(
configuration : configdata_priv,
output : 'expr-config-private.hh',
)
subdir('nix-meson-build-support/common')
parser_tab = custom_target(
input : 'parser.y',
output : [
'parser-tab.cc',
'parser-tab.hh',
],
command : [
'bison',
'-v',
'-o',
'@OUTPUT0@',
'@INPUT@',
'-d',
],
# NOTE(Qyriad): Meson doesn't support installing only part of a custom target, so we add
# an install script below which removes parser-tab.cc.
install : true,
install_dir : get_option('includedir') / 'nix',
)
lexer_tab = custom_target(
input : [
'lexer.l',
parser_tab,
],
output : [
'lexer-tab.cc',
'lexer-tab.hh',
],
command : [
'flex',
'-Cf', # Use full scanner tables
'--outfile',
'@OUTPUT0@',
'--header-file=' + '@OUTPUT1@',
'@INPUT0@',
],
# NOTE(Qyriad): Meson doesn't support installing only part of a custom target, so we add
# an install script below which removes lexer-tab.cc.
install : true,
install_dir : get_option('includedir') / 'nix',
)
subdir('nix-meson-build-support/generate-header')
generated_headers = []
foreach header : [
'imported-drv-to-derivation.nix',
'fetchurl.nix',
]
generated_headers += gen_header.process(header)
endforeach
sources = files(
'attr-path.cc',
'attr-set.cc',
'eval-cache.cc',
'eval-error.cc',
'eval-gc.cc',
'eval-settings.cc',
'eval.cc',
'function-trace.cc',
'get-drvs.cc',
'json-to-value.cc',
'lexer-helpers.cc',
'nixexpr.cc',
'paths.cc',
'primops.cc',
'print-ambiguous.cc',
'print.cc',
'search-path.cc',
'value-to-json.cc',
'value-to-xml.cc',
'value/context.cc',
)
subdir('include/nix/expr')
subdir('primops')
subdir('nix-meson-build-support/export-all-symbols')
subdir('nix-meson-build-support/windows-version')
this_library = library(
'nixexpr',
sources,
config_priv_h,
parser_tab,
lexer_tab,
generated_headers,
dependencies : deps_public + deps_private + deps_other,
include_directories : include_dirs,
link_args: linker_export_flags,
prelink : true, # For C++ static initializers
install : true,
)
install_headers(headers, subdir : 'nix/expr', preserve_path : true)
libraries_private = []
subdir('nix-meson-build-support/export')