diff --git a/docs/markdown/Builtin-options.md b/docs/markdown/Builtin-options.md
index ef327e3b8..f57755c06 100644
--- a/docs/markdown/Builtin-options.md
+++ b/docs/markdown/Builtin-options.md
@@ -119,30 +119,33 @@ no options.
The following options are available. Note that they may not be
available on all platforms or with all compilers:
-| Option | Default value | Possible values | Description |
-| ----------- | ------------- | --------------- | ----------- |
-| b_asneeded | true | true, false | Use -Wl,--as-needed when linking |
-| b_bitcode | false | true, false | Embed Apple bitcode, see below |
-| b_colorout | always | auto, always, never | Use colored output |
-| b_coverage | false | true, false | Enable coverage tracking |
-| b_lundef | true | true, false | Don't allow undefined symbols when linking |
-| b_lto | false | true, false | Use link time optimization |
-| b_ndebug | false | true, false, if-release | Disable asserts |
-| b_pch | true | true, false | Use precompiled headers |
-| b_pgo | off | off, generate, use | Use profile guided optimization |
-| b_sanitize | none | see below | Code sanitizer to use |
-| b_staticpic | true | true, false | Build static libraries as position independent |
-| b_pie | false | true, false | Build position-independent executables (since 0.49.0)|
-| b_vscrt | from_buildtype| none, md, mdd, mt, mtd, from_buildtype, static_from_buildtype | VS runtime library to use (since 0.48.0) (static_from_buildtype since 0.56.0) |
+| Option | Default value | Possible values | Description |
+|---------------|----------------|------------------------------------------------------------------|-------------------------------------------------------------------------------|
+| b_asneeded | true | true, false | Use -Wl,--as-needed when linking |
+| b_bitcode | false | true, false | Embed Apple bitcode, see below |
+| b_colorout | always | auto, always, never | Use colored output |
+| b_coverage | false | true, false | Enable coverage tracking |
+| b_lundef | true | true, false | Don't allow undefined symbols when linking |
+| b_lto | false | true, false | Use link time optimization |
+| b_lto_threads | 0 | Any integer* | Use multiple threads for lto. *(Added in 0.57.0)* |
+| b_ndebug | false | true, false, if-release | Disable asserts |
+| b_pch | true | true, false | Use precompiled headers |
+| b_pgo | off | off, generate, use | Use profile guided optimization |
+| b_sanitize | none | see below | Code sanitizer to use |
+| b_staticpic | true | true, false | Build static libraries as position independent |
+| b_pie | false | true, false | Build position-independent executables (since 0.49.0) |
+| b_vscrt | from_buildtype | none, md, mdd, mt, mtd, from_buildtype, static_from_buildtype | VS runtime library to use (since 0.48.0) (static_from_buildtype since 0.56.0) |
The value of `b_sanitize` can be one of: `none`, `address`, `thread`,
`undefined`, `memory`, `address,undefined`.
- The default value of `b_vscrt`
-is `from_buildtype`. The following table is used internally to pick
-the CRT compiler arguments for `from_buildtype` or
-`static_from_buildtype` *(since 0.56)* based on the value of the
-`buildtype` option:
+* < 0 means disable, == 0 means automatic selection, > 0 sets a specific number to use
+
+
+The default value of `b_vscrt` is `from_buildtype`. The following table is
+used internally to pick the CRT compiler arguments for `from_buildtype` or
+`static_from_buildtype` *(since 0.56)* based on the value of the `buildtype`
+option:
| buildtype | from_buildtype | static_from_buildtype |
| -------- | -------------- | --------------------- |
diff --git a/docs/markdown/snippets/lto_threads.md b/docs/markdown/snippets/lto_threads.md
new file mode 100644
index 000000000..a6f761481
--- /dev/null
+++ b/docs/markdown/snippets/lto_threads.md
@@ -0,0 +1,7 @@
+## Knob to control LTO thread
+
+Both the gnu linker and lld support using threads for speading up LTO, meson
+now provides a knob for this: `-Db_lto_threads`. Currently this is only
+supported for clang and gcc. Any positive integer is supported, `0` means
+`auto`. If the compiler or linker implemnets it's on `auto` we use that,
+otherwise the number of threads on the machine is used.
diff --git a/mesonbuild/compilers/compilers.py b/mesonbuild/compilers/compilers.py
index 0f83f4cae..07569a727 100644
--- a/mesonbuild/compilers/compilers.py
+++ b/mesonbuild/compilers/compilers.py
@@ -268,6 +268,8 @@ clike_debug_args = {False: [],
base_options: 'KeyedOptionDictType' = {
OptionKey('b_pch'): coredata.UserBooleanOption('Use precompiled headers', True),
OptionKey('b_lto'): coredata.UserBooleanOption('Use link time optimization', False),
+ OptionKey('b_lto'): coredata.UserBooleanOption('Use link time optimization', False),
+ OptionKey('b_lto_threads'): coredata.UserIntegerOption('Use multiple threads for Link Time Optimization', (None, None,0)),
OptionKey('b_sanitize'): coredata.UserComboOption('Code sanitizer to use',
['none', 'address', 'thread', 'undefined', 'memory', 'address,undefined'],
'none'),
@@ -300,11 +302,25 @@ def option_enabled(boptions: T.Set[OptionKey], options: 'KeyedOptionDictType',
except KeyError:
return False
+
+def get_option_value(options: 'KeyedOptionDictType', opt: OptionKey, fallback: '_T') -> '_T':
+ """Get the value of an option, or the fallback value."""
+ try:
+ v: '_T' = options[opt].value
+ except KeyError:
+ return fallback
+
+ assert isinstance(v, type(fallback)), f'Should have {type(fallback)!r} but was {type(v)!r}'
+ # Mypy doesn't understand that the above assert ensures that v is type _T
+ return v
+
+
def get_base_compile_args(options: 'KeyedOptionDictType', compiler: 'Compiler') -> T.List[str]:
args = [] # type T.List[str]
try:
if options[OptionKey('b_lto')].value:
- args.extend(compiler.get_lto_compile_args())
+ args.extend(compiler.get_lto_compile_args(
+ threads=get_option_value(options, OptionKey('b_lto_threads'), 0)))
except KeyError:
pass
try:
@@ -926,7 +942,7 @@ class Compiler(metaclass=abc.ABCMeta):
ret.append(arg)
return ret
- def get_lto_compile_args(self) -> T.List[str]:
+ def get_lto_compile_args(self, *, threads: int = 0) -> T.List[str]:
return []
def get_lto_link_args(self) -> T.List[str]:
diff --git a/mesonbuild/compilers/mixins/clang.py b/mesonbuild/compilers/mixins/clang.py
index fcb22258e..9c17a55bd 100644
--- a/mesonbuild/compilers/mixins/clang.py
+++ b/mesonbuild/compilers/mixins/clang.py
@@ -49,7 +49,8 @@ class ClangCompiler(GnuLikeCompiler):
super().__init__()
self.id = 'clang'
self.defines = defines or {}
- self.base_options.add(OptionKey('b_colorout'))
+ self.base_options.update({OptionKey('b_colorout'), OptionKey('b_lto_threads')})
+
# TODO: this really should be part of the linker base_options, but
# linkers don't have base_options.
if isinstance(self.linker, AppleDynamicLinker):
@@ -135,3 +136,10 @@ class ClangCompiler(GnuLikeCompiler):
def get_coverage_link_args(self) -> T.List[str]:
return ['--coverage']
+
+ def get_lto_compile_args(self, *, threads: int = 0) -> T.List[str]:
+ args = super().get_lto_compile_args(threads=threads)
+ # In clang -flto=0 means auto
+ if threads >= 0:
+ args.append(f'-flto-jobs={threads}')
+ return args
diff --git a/mesonbuild/compilers/mixins/gnu.py b/mesonbuild/compilers/mixins/gnu.py
index 95bcd7cc3..5afbb83d5 100644
--- a/mesonbuild/compilers/mixins/gnu.py
+++ b/mesonbuild/compilers/mixins/gnu.py
@@ -17,6 +17,7 @@
import abc
import functools
import os
+import multiprocessing
import pathlib
import re
import subprocess
@@ -281,7 +282,9 @@ class GnuLikeCompiler(Compiler, metaclass=abc.ABCMeta):
return self._split_fetch_real_dirs(line.split('=', 1)[1])
return []
- def get_lto_compile_args(self) -> T.List[str]:
+ def get_lto_compile_args(self, *, threads: int = 0) -> T.List[str]:
+ # This provides a base for many compilers, GCC and Clang override this
+ # for their specific arguments
return ['-flto']
def sanitizer_compile_args(self, value: str) -> T.List[str]:
@@ -330,7 +333,7 @@ class GnuCompiler(GnuLikeCompiler):
super().__init__()
self.id = 'gcc'
self.defines = defines or {}
- self.base_options.add(OptionKey('b_colorout'))
+ self.base_options.update({OptionKey('b_colorout'), OptionKey('b_lto_threads')})
def get_colorout_args(self, colortype: str) -> T.List[str]:
if mesonlib.version_compare(self.version, '>=4.9.0'):
@@ -383,3 +386,13 @@ class GnuCompiler(GnuLikeCompiler):
def get_prelink_args(self, prelink_name: str, obj_list: T.List[str]) -> T.List[str]:
return ['-r', '-o', prelink_name] + obj_list
+
+ def get_lto_compile_args(self, *, threads: int = 0) -> T.List[str]:
+ if threads == 0:
+ if mesonlib.version_compare(self.version, '>= 10.0'):
+ return ['-flto=auto']
+ # This matches clang's behavior of using the number of cpus
+ return [f'-flto={multiprocessing.cpu_count()}']
+ elif threads > 0:
+ return [f'-flto={threads}']
+ return super().get_lto_compile_args(threads=threads)
diff --git a/run_unittests.py b/run_unittests.py
index 2a14f7800..aff94c49b 100755
--- a/run_unittests.py
+++ b/run_unittests.py
@@ -2843,6 +2843,27 @@ class AllPlatformTests(BasePlatformTests):
self.build()
self.run_tests()
+ @skip_if_not_base_option('b_lto_threads')
+ def test_lto_threads(self):
+ testdir = os.path.join(self.common_test_dir, '6 linkshared')
+
+ env = get_fake_env(testdir, self.builddir, self.prefix)
+ cc = env.detect_c_compiler(MachineChoice.HOST)
+ if cc.get_id() == 'clang' and is_windows():
+ raise unittest.SkipTest('LTO not (yet) supported by windows clang')
+
+ self.init(testdir, extra_args=['-Db_lto=true', '-Db_lto_threads=8'])
+ self.build()
+ self.run_tests()
+
+ expected = set(cc.get_lto_compile_args(threads=8))
+ targets = self.introspect('--targets')
+ # This assumes all of the targets support lto
+ for t in targets:
+ for s in t['target_sources']:
+ for e in expected:
+ self.assertIn(e, s['parameters'])
+
def test_dist_git(self):
if not shutil.which('git'):
raise unittest.SkipTest('Git not found')