Merge pull request #8087 from dcbaker/submit/lto-extensions

Add option for thinLTO

3 files changed, 38 insertions, 20 deletions

diff --git a/docs/markdown/Builtin-options.md b/docs/markdown/Builtin-options.md
index ef327e3..2d7c01c 100644
--- a/docs/markdown/Builtin-options.md
+++ b/docs/markdown/Builtin-options.md
@@ -119,30 +119,36 @@ 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_lto_mode    | default        | default, thin                                                    | Select between lto modes, thin and default. *(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`.
 
-<a name="b_vscrt-from_buildtype"></a> 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
+
+LLVM supports `thin` lto, for more discussion see [LLVM's documentation](https://clang.llvm.org/docs/ThinLTO.html)
+
+<a name="b_vscrt-from_buildtype"></a>
+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_mode.md b/docs/markdown/snippets/lto_mode.md
new file mode 100644
index 0000000..c1df066
--- /dev/null
+++ b/docs/markdown/snippets/lto_mode.md
@@ -0,0 +1,5 @@
+## Support added for LLVM's thinLTO
+
+A new `b_lto_mode` option has been added, which may be set to `default` or
+`thin`. Thin only works for clang, and only with gnu gold, lld variants, or
+ld64.
diff --git a/docs/markdown/snippets/lto_threads.md b/docs/markdown/snippets/lto_threads.md
new file mode 100644
index 0000000..a6f7614
--- /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.