blocks|key|416015|text|编辑:截至2015年10月28日，在CMake+IRC上|type|unstyled|depth|inlineStyleRanges|entityRanges|data|416016|jcelerier+%7C+I+have+a+question+about+INTERPROCEDURAL_OPTIMIZATION
jcelerier+%7C+it+sounds+like+it+should+enable+-flto+on+gcc
%2Bngladitz+%7C+jcelerier:+its+only+implemented+for+the+intel+compiler
jcelerier+%7C+ngladitz:+ah,+okay
jcelerier+%7C+are+there+other+switches+for+pgo+/+lto+?
jcelerier+%7C+or+must+it+be+done+by+hand+?
%2Bngladitz+%7C+there+currently+is+no+first+class+support+otherwise+++++|code-block|syntax|javascript|416017|相关CMake问题：https://gitlab.kitware.com/cmake/cmake/issues/15245|offset|length|416018|CMake在目标上具有INTERPROCEDURAL_OPTIMIZATION属性，听起来它可能在某些平台上启用LTO。|style|CODE|416019|链接：OPTIMIZATION.html|416020|若要在目标MyLib上启用它，请执行以下操作：|416021|add_library(MyLib+...)
...
set_property(TARGET+MyLib+PROPERTY+INTERPROCEDURAL_OPTIMIZATION+True)|416022|entityMap|0|LINK|mutability|MUTABLE|url|https://gitlab.kitware.com/cmake/cmake/issues/15245|1|http://www.cmake.org/cmake/help/v3.0/prop_tgt/INTERPROCEDURAL_OPTIMIZATION.html^0|0|0|A|1F|0|0|B|S|0|3|H|1|0|0|0^^$0|@$1|2|3|4|5|6|7|14|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|15|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|16|8|@]|9|@$I|17|J|18|1|19]]|A|$]]|$1|K|3|L|5|6|7|1A|8|@$I|1B|J|1C|M|N]]|9|@]|A|$]]|$1|O|3|P|5|6|7|1D|8|@]|9|@$I|1E|J|1F|1|1G]]|A|$]]|$1|Q|3|R|5|6|7|1H|8|@]|9|@]|A|$]]|$1|S|3|T|5|D|7|1I|8|@]|9|@]|A|$E|F]]|$1|U|3|-4|5|6|7|1J|8|@]|9|@]|A|$]]]|V|$W|$5|X|Y|Z|A|$10|11]]|12|$5|X|Y|Z|A|$10|13]]]]

Edit: as of 28 October, 2015 on CMake IRC

<pre><code>jcelerier | I have a question about INTERPROCEDURAL_OPTIMIZATION
jcelerier | it sounds like it should enable -flto on gcc
+ngladitz | jcelerier: its only implemented for the intel compiler
jcelerier | ngladitz: ah, okay
jcelerier | are there other switches for pgo / lto ?
jcelerier | or must it be done by hand ?
+ngladitz | there currently is no first class support otherwise 
</code></pre>

Related CMake issue: <a href="https://gitlab.kitware.com/cmake/cmake/issues/15245" rel="noreferrer">https://gitlab.kitware.com/cmake/cmake/issues/15245</a>

<hr>

CMake has the <code>INTERPROCEDURAL_OPTIMIZATION</code> property on targets, which sounds like it may enable LTO on some platforms.

Link : <a href="http://www.cmake.org/cmake/help/v3.0/prop_tgt/INTERPROCEDURAL_OPTIMIZATION.html" rel="noreferrer">http://www.cmake.org/cmake/help/v3.0/prop_tgt/INTERPROCEDURAL_OPTIMIZATION.html</a>

To enable it on a target MyLib :

<pre><code>add_library(MyLib ...)
...
set_property(TARGET MyLib PROPERTY INTERPROCEDURAL_OPTIMIZATION True)
</code></pre>

blocks|key|1619128|text|是的，根据源代码，对gcc/clang编译器不支持LTO。他们只对Intel编译器有一些支持。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1619129|我有一些cmake+3.4.3的grep输出：|1619130|grep+-HiR+'INTERPROCEDURAL_OPTIMIZATION'+*
Help/manual/cmake-properties.7.rst:++
/prop_dir/INTERPROCEDURAL_OPTIMIZATION_CONFIG
Help/manual/cmake-properties.7.rst:++
/prop_dir/INTERPROCEDURAL_OPTIMIZATION
Help/manual/cmake-properties.7.rst:++
/prop_tgt/INTERPROCEDURAL_OPTIMIZATION_CONFIG
Help/manual/cmake-properties.7.rst:++
/prop_tgt/INTERPROCEDURAL_OPTIMIZATION
Help/prop_dir/INTERPROCEDURAL_OPTIMIZATION.rst:INTERPROCEDURAL_OPTIMIZATION
Help/prop_dir/INTERPROCEDURAL_OPTIMIZATION_CONFIG.rst:INTERPROCEDURAL_OPTIMIZATION_<CONFIG++++
Help/prop_dir/INTERPROCEDURAL_OPTIMIZATION_CONFIG.rst:This+is+a
per-configuration+version+of+INTERPROCEDURAL_OPTIMIZATION.
Help/prop_tgt/INTERPROCEDURAL_OPTIMIZATION.rst:INTERPROCEDURAL_OPTIMIZATION
Help/prop_tgt/INTERPROCEDURAL_OPTIMIZATION_CONFIG.rst:INTERPROCEDURAL_OPTIMIZATION_<CONFIG++++
Help/prop_tgt/INTERPROCEDURAL_OPTIMIZATION_CONFIG.rst:This+is+a
per-configuration+version+of+INTERPROCEDURAL_OPTIMIZATION.
Modules/Platform/Linux-Intel.cmake:++++#+INTERPROCEDURAL_OPTIMIZATION
Source/cmCommonTargetGenerator.cxx:+
if(this->GetFeatureAsBool("INTERPROCEDURAL_OPTIMIZATION"))
Source/cmGeneratorTarget.cxx:++++++++++
"INTERPROCEDURAL_OPTIMIZATION",+config))
Source/cmMakefileLibraryTargetGenerator.cxx:+
if(this->GetFeatureAsBool("INTERPROCEDURAL_OPTIMIZATION")+&&
Tests/IPO/CMakeLists.txt:set_property(DIRECTORY+PROPERTY
INTERPROCEDURAL_OPTIMIZATION+1)|code-block|syntax|javascript|1619131|如您所见，我们只有Intel平台模块。|1619132|因此，我为这个非常有用的特性创建了特性请求：https://cmake.org/Bug/view.php?id=15939|offset|length|1619133|entityMap|0|LINK|mutability|MUTABLE|url|https://cmake.org/Bug/view.php?id=15939^0|0|0|0|0|M|13|0|0^^$0|@$1|2|3|4|5|6|7|W|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|X|8|@]|9|@]|A|$]]|$1|D|3|E|5|F|7|Y|8|@]|9|@]|A|$G|H]]|$1|I|3|J|5|6|7|Z|8|@]|9|@]|A|$]]|$1|K|3|L|5|6|7|10|8|@]|9|@$M|11|N|12|1|13]]|A|$]]|$1|O|3|-4|5|6|7|14|8|@]|9|@]|A|$]]]|P|$Q|$5|R|S|T|A|$U|V]]]]

Yep, according to source code there are no support for LTO for gcc/clang compilers. They have some support for Intel compiler only.

I have some grep output for cmake 3.4.3:

<pre><code>grep -HiR 'INTERPROCEDURAL_OPTIMIZATION' *
Help/manual/cmake-properties.7.rst: 
/prop_dir/INTERPROCEDURAL_OPTIMIZATION_CONFIG
Help/manual/cmake-properties.7.rst: 
/prop_dir/INTERPROCEDURAL_OPTIMIZATION
Help/manual/cmake-properties.7.rst: 
/prop_tgt/INTERPROCEDURAL_OPTIMIZATION_CONFIG
Help/manual/cmake-properties.7.rst: 
/prop_tgt/INTERPROCEDURAL_OPTIMIZATION
Help/prop_dir/INTERPROCEDURAL_OPTIMIZATION.rst:INTERPROCEDURAL_OPTIMIZATION
Help/prop_dir/INTERPROCEDURAL_OPTIMIZATION_CONFIG.rst:INTERPROCEDURAL_OPTIMIZATION_&lt;CONFIG 
Help/prop_dir/INTERPROCEDURAL_OPTIMIZATION_CONFIG.rst:This is a
per-configuration version of INTERPROCEDURAL_OPTIMIZATION.
Help/prop_tgt/INTERPROCEDURAL_OPTIMIZATION.rst:INTERPROCEDURAL_OPTIMIZATION
Help/prop_tgt/INTERPROCEDURAL_OPTIMIZATION_CONFIG.rst:INTERPROCEDURAL_OPTIMIZATION_&lt;CONFIG 
Help/prop_tgt/INTERPROCEDURAL_OPTIMIZATION_CONFIG.rst:This is a
per-configuration version of INTERPROCEDURAL_OPTIMIZATION.
Modules/Platform/Linux-Intel.cmake: # INTERPROCEDURAL_OPTIMIZATION
Source/cmCommonTargetGenerator.cxx: 
if(this-&gt;GetFeatureAsBool("INTERPROCEDURAL_OPTIMIZATION"))
Source/cmGeneratorTarget.cxx: 
"INTERPROCEDURAL_OPTIMIZATION", config))
Source/cmMakefileLibraryTargetGenerator.cxx: 
if(this-&gt;GetFeatureAsBool("INTERPROCEDURAL_OPTIMIZATION") &amp;&amp;
Tests/IPO/CMakeLists.txt:set_property(DIRECTORY PROPERTY
INTERPROCEDURAL_OPTIMIZATION 1)
</code></pre>

As you can see we have only Intel platform module.

So I have created feature request for this extremely useful feature: <a href="https://cmake.org/Bug/view.php?id=15939" rel="nofollow">https://cmake.org/Bug/view.php?id=15939</a>

blocks|key|415148|text|好消息！CMake+v3.9最终支持LTO。|type|unstyled|depth|inlineStyleRanges|offset|length|style|BOLD|entityRanges|data|415149|示例|415150|下面是演示它如何工作的示例代码：|415151|cmake_minimum_required(VERSION+3.9.4)

include(CheckIPOSupported)
check_ipo_supported(RESULT+supported+OUTPUT+error)

add_executable(example+Example.cpp)

if(+supported+)
++++message(STATUS+"IPO+/+LTO+enabled")
++++set_property(TARGET+example+PROPERTY+INTERPROCEDURAL_OPTIMIZATION+TRUE)
else()
++++message(STATUS+"IPO+/+LTO+not+supported:+<${error}>")
endif()|code-block|syntax|javascript|415152|对于GCC来说，这将-flto+-fno-fat-lto-objects添加到目标编译命令中。|CODE|415153|检查编译器支持|415154|模块https://cmake.org/cmake/help/latest/module/CheckIPOSupported.html#module:CheckIPOSupported提供检查编译器是否支持过程间优化(IPO/LTO)：|415155|check_ipo_supported([RESULT+<result>]+[OUTPUT+<output>]
++++++++++++++++++++[LANGUAGES+<lang>...])|415156|如果没有传递任何参数(=+check_ipo_supported())，则会引发错误以指示不支持该参数，否则result变量将被设置为YES或NO。更多细节将在该模块的文档中描述。|415157|使能LTO|415158|LTO可用于单个目标，也可作为所有目标的默认启用。|415159|用于单个目标的LTO|415160|若要为目标集INTERPROCEDURAL_OPTIMIZATION启用LTO，请将其设置为TRUE。这是由set_property()命令完成的：|415161|set_property(TARGET+name-target-here
+++++++++++++PROPERTY+INTERPROCEDURAL_OPTIMIZATION+TRUE)|415162|LTO作为默认|415163|通过将CMAKE_INTERPROCEDURAL_OPTIMIZATION设置为TRUE，可以对每个缺省值启用LTO|415164|set(CMAKE_INTERPROCEDURAL_OPTIMIZATION+TRUE)|415165|这将为该行之后创建的所有目标启用INTERPROCEDURAL_OPTIMIZATION。以前创建的不受影响。|415166|另请参阅|415167|CMake问题|unordered-list-item|415168|相关拉请求|415169|entityMap|0|LINK|mutability|MUTABLE|url|https://cmake.org/cmake/help/latest/module/CheckIPOSupported.html#module:CheckIPOSupported|1|https://cmake.org/cmake/help/latest/prop_tgt/INTERPROCEDURAL_OPTIMIZATION.html|2|https://cmake.org/cmake/help/latest/command/set_property.html|3|https://cmake.org/cmake/help/latest/variable/CMAKE_INTERPROCEDURAL_OPTIMIZATION.html|4|https://gitlab.kitware.com/cmake/cmake/issues/15245|5|https://gitlab.kitware.com/cmake/cmake/merge_requests?scope=all&utf8=%25E2%259C%2593&state=merged&label_name%255B%255D=area%253Aipo^0|4|A|G|5|0|0|0|0|A|Q|0|0|30|9|2|2I|0|0|0|D|L|1I|6|1V|3|1Z|2|0|0|6|4|K|2|0|0|1A|4|6|S|1|1I|E|2|0|0|0|14|4|3|Y|3|0|0|G|S|0|0|0|7|4|0|0|5|5|0^^$0|@$1|2|3|4|5|6|7|26|8|@$9|27|A|28|B|C]|$9|29|A|2A|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|2B|8|@]|D|@]|E|$]]|$1|H|3|I|5|6|7|2C|8|@]|D|@]|E|$]]|$1|J|3|K|5|L|7|2D|8|@]|D|@]|E|$M|N]]|$1|O|3|P|5|6|7|2E|8|@$9|2F|A|2G|B|Q]]|D|@]|E|$]]|$1|R|3|S|5|6|7|2H|8|@]|D|@]|E|$]]|$1|T|3|U|5|6|7|2I|8|@$9|2J|A|2K|B|C]]|D|@$9|2L|A|2M|1|2N]]|E|$]]|$1|V|3|W|5|L|7|2O|8|@]|D|@]|E|$M|N]]|$1|X|3|Y|5|6|7|2P|8|@$9|2Q|A|2R|B|Q]|$9|2S|A|2T|B|Q]|$9|2U|A|2V|B|Q]|$9|2W|A|2X|B|Q]]|D|@]|E|$]]|$1|Z|3|10|5|6|7|2Y|8|@]|D|@]|E|$]]|$1|11|3|12|5|6|7|2Z|8|@$9|30|A|31|B|C]|$9|32|A|33|B|C]]|D|@]|E|$]]|$1|13|3|14|5|6|7|34|8|@]|D|@]|E|$]]|$1|15|3|16|5|6|7|35|8|@$9|36|A|37|B|Q]]|D|@$9|38|A|39|1|3A]|$9|3B|A|3C|1|3D]]|E|$]]|$1|17|3|18|5|L|7|3E|8|@]|D|@]|E|$M|N]]|$1|19|3|1A|5|6|7|3F|8|@]|D|@]|E|$]]|$1|1B|3|1C|5|6|7|3G|8|@$9|3H|A|3I|B|Q]]|D|@$9|3J|A|3K|1|3L]]|E|$]]|$1|1D|3|1E|5|L|7|3M|8|@]|D|@]|E|$M|N]]|$1|1F|3|1G|5|6|7|3N|8|@$9|3O|A|3P|B|Q]]|D|@]|E|$]]|$1|1H|3|1I|5|6|7|3Q|8|@]|D|@]|E|$]]|$1|1J|3|1K|5|1L|7|3R|8|@]|D|@$9|3S|A|3T|1|3U]]|E|$]]|$1|1M|3|1N|5|1L|7|3V|8|@]|D|@$9|3W|A|3X|1|3Y]]|E|$]]|$1|1O|3|-4|5|6|7|3Z|8|@]|D|@]|E|$]]]|1P|$1Q|$5|1R|1S|1T|E|$1U|1V]]|1W|$5|1R|1S|1T|E|$1U|1X]]|1Y|$5|1R|1S|1T|E|$1U|1Z]]|20|$5|1R|1S|1T|E|$1U|21]]|22|$5|1R|1S|1T|E|$1U|23]]|24|$5|1R|1S|1T|E|$1U|25]]]]

Good news! CMake v3.9 finally supports LTO.
<hr />
<h1>Example</h1>
Here's an example code to show how it works:
<pre><code>cmake_minimum_required(VERSION 3.9.4)

include(CheckIPOSupported)
check_ipo_supported(RESULT supported OUTPUT error)

add_executable(example Example.cpp)

if( supported )
 message(STATUS &quot;IPO / LTO enabled&quot;)
 set_property(TARGET example PROPERTY INTERPROCEDURAL_OPTIMIZATION TRUE)
else()
 message(STATUS &quot;IPO / LTO not supported: &lt;${error}&gt;&quot;)
endif()
</code></pre>
For GCC this adds <code>-flto -fno-fat-lto-objects</code> to the targets compile commands.
<hr />
<h1>Checking Compiler Support</h1>
The Module <a href="https://cmake.org/cmake/help/latest/module/CheckIPOSupported.html#module:CheckIPOSupported" rel="nofollow noreferrer">CheckIPOSupported</a> provides checking whether interprocedural optimization (IPO/LTO) is supported by the compiler or not:
<pre><code>check_ipo_supported([RESULT &lt;result&gt;] [OUTPUT &lt;output&gt;]
 [LANGUAGES &lt;lang&gt;...])
</code></pre>
If no arguments is passed (= <code>check_ipo_supported()</code>) an error is raised to indicate it's not supported, otherwise the <code>result</code> variable is set to either <code>YES</code> or <code>NO</code>. More details are described in the documentation of the module.
<hr />
<h2>Enabling LTO</h2>
LTO is enabled either for a single target or as default for all targets.
<h3>LTO for a single target</h3>
To enable LTO for a target set <a href="https://cmake.org/cmake/help/latest/prop_tgt/INTERPROCEDURAL_OPTIMIZATION.html" rel="nofollow noreferrer"><code>INTERPROCEDURAL_OPTIMIZATION</code></a> to <code>TRUE</code>. This is done by the <a href="https://cmake.org/cmake/help/latest/command/set_property.html" rel="nofollow noreferrer"><code>set_property()</code></a> command:
<pre><code>set_property(TARGET name-target-here
 PROPERTY INTERPROCEDURAL_OPTIMIZATION TRUE)
</code></pre>
<h3>LTO as default</h3>
It's possible to enable LTO per default by setting <a href="https://cmake.org/cmake/help/latest/variable/CMAKE_INTERPROCEDURAL_OPTIMIZATION.html" rel="nofollow noreferrer"><code>CMAKE_INTERPROCEDURAL_OPTIMIZATION</code></a> to <code>TRUE</code>:
<pre><code>set(CMAKE_INTERPROCEDURAL_OPTIMIZATION TRUE)
</code></pre>
This will enable <code>INTERPROCEDURAL_OPTIMIZATION</code> for all targets created after this line. Those created before are not affected.
<hr />
<h3>See also</h3>
<ul>
<li><a href="https://gitlab.kitware.com/cmake/cmake/issues/15245" rel="nofollow noreferrer">CMake issue</a></li>
<li><a href="https://gitlab.kitware.com/cmake/cmake/merge_requests?scope=all&amp;utf8=%E2%9C%93&amp;state=merged&amp;label_name%5B%5D=area%3Aipo" rel="nofollow noreferrer">Related Pull Requests</a></li>
</ul>

blocks|key|416098|text|目前gcc和clang都支持lto。(参见：https://clang.llvm.org/docs/CommandGuide/clang.html+https://gcc.gnu.org/onlinedocs/gcc/Optimize-Options.html+)您可以在via+cmake:+set+(CMAKE_INTERPROCEDURAL_OPTIMIZATION+True)中启用它，但是您需要拥有版本cmake+>=+3.9，我认为可以设置一些策略并检查编译器/工具链是否支持LTO+(检查CMAKE_IPO_AVAILABLE，否则抛出错误)。|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|416099|并为gcc/clang设置标志(+fcc+>4.7的-flto和-ffat-lto-文件或clang的-flto=full/thin+)|416100|entityMap|0|LINK|mutability|MUTABLE|url|https://clang.llvm.org/docs/CommandGuide/clang.html|1|https://gcc.gnu.org/onlinedocs/gcc/Optimize-Options.html^0|M|1F|0|22|1K|1|0|0^^$0|@$1|2|3|4|5|6|7|P|8|@]|9|@$A|Q|B|R|1|S]|$A|T|B|U|1|V]]|C|$]]|$1|D|3|E|5|6|7|W|8|@]|9|@]|C|$]]|$1|F|3|-4|5|6|7|X|8|@]|9|@]|C|$]]]|G|$H|$5|I|J|K|C|$L|M]]|N|$5|I|J|K|C|$L|O]]]]

At the moment both gcc and clang support lto.
(See: <a href="https://clang.llvm.org/docs/CommandGuide/clang.html" rel="nofollow noreferrer">https://clang.llvm.org/docs/CommandGuide/clang.html</a> 
<a href="https://gcc.gnu.org/onlinedocs/gcc/Optimize-Options.html" rel="nofollow noreferrer">https://gcc.gnu.org/onlinedocs/gcc/Optimize-Options.html</a>
)
You can enable it in via cmake: 
set (CMAKE_INTERPROCEDURAL_OPTIMIZATION True)
However you need to have version cmake >= 3.9, and I think may be set some policy and check whether LTO is supported by the compiler / toolchain ( check CMAKE_IPO_AVAILABLE and throw error otherwise)

And set flags for gcc/clang ( -flto and -ffat-lto-files for fcc >4.7 or -flto=full/thin for clang)

I have the most recent cmake build and trying all build configurations (Debug, MinSizeRel, RelWithDebugInfo, Release, General) I see nowhere (text search) in generated makefiles the string <code>-lto</code>, so or the functionality is still not present, or it requires manual intervertion (in that case a text search for LTO or Link time optimization) over the documentation gives no result, so I see nowhere in official documentation a way to enable LTO.

Is there any way to enable LTO "globally" (for all compilers) without specifying manually flags that could be at worst supported only by GCC?

How do I enable link time optimization (LTO) with CMake?

翻译质量差，导致语言生硬或混乱。

没有提供实际的解决方法或示例。

解答不清晰，无法理解或解决问题。

页面排版不美观，阅读体验差。

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我有最新的cmake，并尝试了所有构建配置(调试、MinSizeRel、RelWithDebugInfo、Release、General) --在生成的makefile字符串-lto中没有看到(文本搜索)，所以或者该功能仍然不存在，或者它需要手动交互(在这种情况下，文档中对LTO或链接时间优化的文本搜索)没有结果，所以...

问如何使用CMake启用链接时间优化(LTO)？
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