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<h3 class="section">7.6 Support for testing link-time optimizations</h3>
<p>Tests for link-time optimizations usually require multiple source files
that are compiled separately, perhaps with different sets of options.
There are several special-purpose test directives used for these tests.
<dl>
<dt><code>{ dg-lto-do </code><var>do-what-keyword</var><code> }</code><dd><var>do-what-keyword</var> specifies how the test is compiled and whether
it is executed. It is one of:
<dl>
<dt><code>assemble</code><dd>Compile with <samp><span class="option">-c</span></samp> to produce a relocatable object file.
<br><dt><code>link</code><dd>Compile, assemble, and link to produce an executable file.
<br><dt><code>run</code><dd>Produce and run an executable file, which is expected to return
an exit code of 0.
</dl>
<p>The default is <code>assemble</code>. That can be overridden for a set of
tests by redefining <code>dg-do-what-default</code> within the <code>.exp</code>
file for those tests.
<p>Unlike <code>dg-do</code>, <code>dg-lto-do</code> does not support an optional
‘<samp><span class="samp">target</span></samp>’ or ‘<samp><span class="samp">xfail</span></samp>’ list. Use <code>dg-skip-if</code>,
<code>dg-xfail-if</code>, or <code>dg-xfail-run-if</code>.
<br><dt><code>{ dg-lto-options { { </code><var>options</var><code> } [{ </code><var>options</var><code> }] } [{ target </code><var>selector</var><code> }]}</code><dd>This directive provides a list of one or more sets of compiler options
to override <var>LTO_OPTIONS</var>. Each test will be compiled and run with
each of these sets of options.
<br><dt><code>{ dg-extra-ld-options </code><var>options</var><code> [{ target </code><var>selector</var><code> }]}</code><dd>This directive adds <var>options</var> to the linker options used.
<br><dt><code>{ dg-suppress-ld-options </code><var>options</var><code> [{ target </code><var>selector</var><code> }]}</code><dd>This directive removes <var>options</var> from the set of linker options used.
</dl>
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