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<div class="section" id="remarks">
<h1>Remarks<a class="headerlink" href="#remarks" title="Permalink to this headline">¶</a></h1>
<div class="contents local topic" id="contents">
<ul class="simple">
<li><p><a class="reference internal" href="#introduction-to-the-llvm-remark-diagnostics" id="id1">Introduction to the LLVM remark diagnostics</a></p></li>
<li><p><a class="reference internal" href="#enabling-optimization-remarks" id="id2">Enabling optimization remarks</a></p>
<ul>
<li><p><a class="reference internal" href="#remark-diagnostics" id="id3">Remark diagnostics</a></p></li>
<li><p><a class="reference internal" href="#serialized-remarks" id="id4">Serialized remarks</a></p></li>
</ul>
</li>
<li><p><a class="reference internal" href="#serialization-modes" id="id5">Serialization modes</a></p></li>
<li><p><a class="reference internal" href="#yaml-remarks" id="id6">YAML remarks</a></p>
<ul>
<li><p><a class="reference internal" href="#yaml-with-a-string-table" id="id7">YAML with a string table</a></p></li>
<li><p><a class="reference internal" href="#yaml-metadata" id="id8">YAML metadata</a></p></li>
</ul>
</li>
<li><p><a class="reference internal" href="#llvm-bitstream-remarks" id="id9">LLVM bitstream remarks</a></p>
<ul>
<li><p><a class="reference internal" href="#meta-block" id="id10">META_BLOCK</a></p></li>
<li><p><a class="reference internal" href="#remark-block" id="id11">REMARK_BLOCK</a></p></li>
<li><p><a class="reference internal" href="#the-remark-container" id="id12">The remark container</a></p></li>
</ul>
</li>
<li><p><a class="reference internal" href="#opt-viewer" id="id13">opt-viewer</a></p>
<ul>
<li><p><a class="reference internal" href="#opt-viewer-py" id="id14">opt-viewer.py</a></p></li>
<li><p><a class="reference internal" href="#opt-stats-py" id="id15">opt-stats.py</a></p></li>
<li><p><a class="reference internal" href="#opt-diff-py" id="id16">opt-diff.py</a></p></li>
</ul>
</li>
<li><p><a class="reference internal" href="#emitting-remark-diagnostics-in-the-object-file" id="id17">Emitting remark diagnostics in the object file</a></p></li>
<li><p><a class="reference internal" href="#c-api" id="id18">C API</a></p></li>
<li><p><a class="reference internal" href="#remark-streamers" id="id19">Remark streamers</a></p></li>
</ul>
</div>
<div class="section" id="introduction-to-the-llvm-remark-diagnostics">
<h2><a class="toc-backref" href="#id1">Introduction to the LLVM remark diagnostics</a><a class="headerlink" href="#introduction-to-the-llvm-remark-diagnostics" title="Permalink to this headline">¶</a></h2>
<p>LLVM is able to emit diagnostics from passes describing whether an optimization
has been performed or missed for a particular reason, which should give more
insight to users about what the compiler did during the compilation pipeline.</p>
<p>There are three main remark types:</p>
<p><code class="docutils literal notranslate"><span class="pre">Passed</span></code></p>
<blockquote>
<div><p>Remarks that describe a successful optimization performed by the compiler.</p>
<dl class="field-list simple">
<dt class="field-odd">Example</dt>
<dd class="field-odd"><p></p></dd>
</dl>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">foo</span> <span class="n">inlined</span> <span class="n">into</span> <span class="n">bar</span> <span class="k">with</span> <span class="p">(</span><span class="n">cost</span><span class="o">=</span><span class="n">always</span><span class="p">):</span> <span class="n">always</span> <span class="n">inline</span> <span class="n">attribute</span>
</pre></div>
</div>
</div></blockquote>
<p><code class="docutils literal notranslate"><span class="pre">Missed</span></code></p>
<blockquote>
<div><p>Remarks that describe an attempt to an optimization by the compiler that
could not be performed.</p>
<dl class="field-list simple">
<dt class="field-odd">Example</dt>
<dd class="field-odd"><p></p></dd>
</dl>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">foo</span> <span class="ow">not</span> <span class="n">inlined</span> <span class="n">into</span> <span class="n">bar</span> <span class="n">because</span> <span class="n">it</span> <span class="n">should</span> <span class="n">never</span> <span class="n">be</span> <span class="n">inlined</span>
<span class="p">(</span><span class="n">cost</span><span class="o">=</span><span class="n">never</span><span class="p">):</span> <span class="n">noinline</span> <span class="n">function</span> <span class="n">attribute</span>
</pre></div>
</div>
</div></blockquote>
<p><code class="docutils literal notranslate"><span class="pre">Analysis</span></code></p>
<blockquote>
<div><p>Remarks that describe the result of an analysis, that can bring more
information to the user regarding the generated code.</p>
<dl class="field-list simple">
<dt class="field-odd">Example</dt>
<dd class="field-odd"><p></p></dd>
</dl>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="mi">16</span> <span class="n">stack</span> <span class="nb">bytes</span> <span class="ow">in</span> <span class="n">function</span>
</pre></div>
</div>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="mi">10</span> <span class="n">instructions</span> <span class="ow">in</span> <span class="n">function</span>
</pre></div>
</div>
</div></blockquote>
</div>
<div class="section" id="enabling-optimization-remarks">
<h2><a class="toc-backref" href="#id2">Enabling optimization remarks</a><a class="headerlink" href="#enabling-optimization-remarks" title="Permalink to this headline">¶</a></h2>
<p>There are two modes that are supported for enabling optimization remarks in
LLVM: through remark diagnostics, or through serialized remarks.</p>
<div class="section" id="remark-diagnostics">
<h3><a class="toc-backref" href="#id3">Remark diagnostics</a><a class="headerlink" href="#remark-diagnostics" title="Permalink to this headline">¶</a></h3>
<p>Optimization remarks can be emitted as diagnostics. These diagnostics will be
propagated to front-ends if desired, or emitted by tools like <a class="reference internal" href="CommandGuide/llc.html"><span class="doc">llc</span></a> or <a class="reference internal" href="CommandGuide/opt.html"><span class="doc">opt</span></a>.</p>
<dl class="std option">
<dt id="cmdoption-pass-remarks">
<code class="sig-name descname"><span class="pre">-pass-remarks</span></code><code class="sig-prename descclassname"><span class="pre">=<regex></span></code><a class="headerlink" href="#cmdoption-pass-remarks" title="Permalink to this definition">¶</a></dt>
<dd><p>Enables optimization remarks from passes whose name match the given (POSIX)
regular expression.</p>
</dd></dl>
<dl class="std option">
<dt id="cmdoption-pass-remarks-missed">
<code class="sig-name descname"><span class="pre">-pass-remarks-missed</span></code><code class="sig-prename descclassname"><span class="pre">=<regex></span></code><a class="headerlink" href="#cmdoption-pass-remarks-missed" title="Permalink to this definition">¶</a></dt>
<dd><p>Enables missed optimization remarks from passes whose name match the given
(POSIX) regular expression.</p>
</dd></dl>
<dl class="std option">
<dt id="cmdoption-pass-remarks-analysis">
<code class="sig-name descname"><span class="pre">-pass-remarks-analysis</span></code><code class="sig-prename descclassname"><span class="pre">=<regex></span></code><a class="headerlink" href="#cmdoption-pass-remarks-analysis" title="Permalink to this definition">¶</a></dt>
<dd><p>Enables optimization analysis remarks from passes whose name match the given
(POSIX) regular expression.</p>
</dd></dl>
</div>
<div class="section" id="serialized-remarks">
<h3><a class="toc-backref" href="#id4">Serialized remarks</a><a class="headerlink" href="#serialized-remarks" title="Permalink to this headline">¶</a></h3>
<p>While diagnostics are useful during development, it is often more useful to
refer to optimization remarks post-compilation, typically during performance
analysis.</p>
<p>For that, LLVM can serialize the remarks produced for each compilation unit to
a file that can be consumed later.</p>
<p>By default, the format of the serialized remarks is <a class="reference internal" href="#yamlremarks"><span class="std std-ref">YAML</span></a>, and it can be accompanied by a <a class="reference internal" href="#remarkssection"><span class="std std-ref">section</span></a>
in the object files to easily retrieve it.</p>
<p><a class="reference internal" href="CommandGuide/llc.html"><span class="doc">llc</span></a> and <a class="reference internal" href="CommandGuide/opt.html"><span class="doc">opt</span></a> support the
following options:</p>
<p><code class="docutils literal notranslate"><span class="pre">Basic</span> <span class="pre">options</span></code></p>
<blockquote>
<div><dl class="std option">
<dt id="cmdoption-pass-remarks-output">
<code class="sig-name descname"><span class="pre">-pass-remarks-output</span></code><code class="sig-prename descclassname"><span class="pre">=<filename></span></code><a class="headerlink" href="#cmdoption-pass-remarks-output" title="Permalink to this definition">¶</a></dt>
<dd><p>Enables the serialization of remarks to a file specified in <filename>.</p>
<p>By default, the output is serialized to <a class="reference internal" href="#yamlremarks"><span class="std std-ref">YAML</span></a>.</p>
</dd></dl>
<dl class="std option">
<dt id="cmdoption-pass-remarks-format">
<code class="sig-name descname"><span class="pre">-pass-remarks-format</span></code><code class="sig-prename descclassname"><span class="pre">=<format></span></code><a class="headerlink" href="#cmdoption-pass-remarks-format" title="Permalink to this definition">¶</a></dt>
<dd><p>Specifies the output format of the serialized remarks.</p>
<p>Supported formats:</p>
<ul class="simple">
<li><p><a class="reference internal" href="#yamlremarks"><span class="std std-ref">yaml</span></a> (default)</p></li>
<li><p><a class="reference internal" href="#yamlstrtabremarks"><span class="std std-ref">yaml-strtab</span></a></p></li>
<li><p><a class="reference internal" href="#bitstreamremarks"><span class="std std-ref">bitstream</span></a></p></li>
</ul>
</dd></dl>
</div></blockquote>
<p><code class="docutils literal notranslate"><span class="pre">Content</span> <span class="pre">configuration</span></code></p>
<blockquote>
<div><dl class="std option">
<dt id="cmdoption-pass-remarks-filter">
<code class="sig-name descname"><span class="pre">-pass-remarks-filter</span></code><code class="sig-prename descclassname"><span class="pre">=<regex></span></code><a class="headerlink" href="#cmdoption-pass-remarks-filter" title="Permalink to this definition">¶</a></dt>
<dd><p>Only passes whose name match the given (POSIX) regular expression will be
serialized to the final output.</p>
</dd></dl>
<dl class="std option">
<dt id="cmdoption-pass-remarks-with-hotness">
<code class="sig-name descname"><span class="pre">-pass-remarks-with-hotness</span></code><code class="sig-prename descclassname"></code><a class="headerlink" href="#cmdoption-pass-remarks-with-hotness" title="Permalink to this definition">¶</a></dt>
<dd><p>With PGO, include profile count in optimization remarks.</p>
</dd></dl>
<dl class="std option">
<dt id="cmdoption-pass-remarks-hotness-threshold">
<code class="sig-name descname"><span class="pre">-pass-remarks-hotness-threshold</span></code><code class="sig-prename descclassname"></code><a class="headerlink" href="#cmdoption-pass-remarks-hotness-threshold" title="Permalink to this definition">¶</a></dt>
<dd><p>The minimum profile count required for an optimization remark to be
emitted.</p>
</dd></dl>
</div></blockquote>
<p>Other tools that support remarks:</p>
<p><strong class="program">llvm-lto</strong></p>
<blockquote>
<div><dl class="std option">
<dt id="cmdoption-lto-pass-remarks-output">
<code class="sig-name descname"><span class="pre">-lto-pass-remarks-output</span></code><code class="sig-prename descclassname"><span class="pre">=<filename></span></code><a class="headerlink" href="#cmdoption-lto-pass-remarks-output" title="Permalink to this definition">¶</a></dt>
<dd></dd></dl>
<dl class="std option">
<dt id="cmdoption-lto-pass-remarks-filter">
<code class="sig-name descname"><span class="pre">-lto-pass-remarks-filter</span></code><code class="sig-prename descclassname"><span class="pre">=<regex></span></code><a class="headerlink" href="#cmdoption-lto-pass-remarks-filter" title="Permalink to this definition">¶</a></dt>
<dd></dd></dl>
<dl class="std option">
<dt id="cmdoption-lto-pass-remarks-format">
<code class="sig-name descname"><span class="pre">-lto-pass-remarks-format</span></code><code class="sig-prename descclassname"><span class="pre">=<format></span></code><a class="headerlink" href="#cmdoption-lto-pass-remarks-format" title="Permalink to this definition">¶</a></dt>
<dd></dd></dl>
<dl class="std option">
<dt id="cmdoption-lto-pass-remarks-with-hotness">
<code class="sig-name descname"><span class="pre">-lto-pass-remarks-with-hotness</span></code><code class="sig-prename descclassname"></code><a class="headerlink" href="#cmdoption-lto-pass-remarks-with-hotness" title="Permalink to this definition">¶</a></dt>
<dd></dd></dl>
<dl class="std option">
<dt id="cmdoption-lto-pass-remarks-hotness-threshold">
<code class="sig-name descname"><span class="pre">-lto-pass-remarks-hotness-threshold</span></code><code class="sig-prename descclassname"></code><a class="headerlink" href="#cmdoption-lto-pass-remarks-hotness-threshold" title="Permalink to this definition">¶</a></dt>
<dd></dd></dl>
</div></blockquote>
<p><strong class="program">gold-plugin</strong> and <strong class="program">lld</strong></p>
<blockquote>
<div><dl class="std option">
<dt id="cmdoption-opt-remarks-filename">
<code class="sig-name descname"><span class="pre">-opt-remarks-filename</span></code><code class="sig-prename descclassname"><span class="pre">=<filename></span></code><a class="headerlink" href="#cmdoption-opt-remarks-filename" title="Permalink to this definition">¶</a></dt>
<dd></dd></dl>
<dl class="std option">
<dt id="cmdoption-opt-remarks-filter">
<code class="sig-name descname"><span class="pre">-opt-remarks-filter</span></code><code class="sig-prename descclassname"><span class="pre">=<regex></span></code><a class="headerlink" href="#cmdoption-opt-remarks-filter" title="Permalink to this definition">¶</a></dt>
<dd></dd></dl>
<dl class="std option">
<dt id="cmdoption-opt-remarks-format">
<code class="sig-name descname"><span class="pre">-opt-remarks-format</span></code><code class="sig-prename descclassname"><span class="pre">=<format></span></code><a class="headerlink" href="#cmdoption-opt-remarks-format" title="Permalink to this definition">¶</a></dt>
<dd></dd></dl>
<dl class="std option">
<dt id="cmdoption-opt-remarks-with-hotness">
<code class="sig-name descname"><span class="pre">-opt-remarks-with-hotness</span></code><code class="sig-prename descclassname"></code><a class="headerlink" href="#cmdoption-opt-remarks-with-hotness" title="Permalink to this definition">¶</a></dt>
<dd></dd></dl>
</div></blockquote>
</div>
</div>
<div class="section" id="serialization-modes">
<h2><a class="toc-backref" href="#id5">Serialization modes</a><a class="headerlink" href="#serialization-modes" title="Permalink to this headline">¶</a></h2>
<p>There are two modes available for serializing remarks:</p>
<p><code class="docutils literal notranslate"><span class="pre">Separate</span></code></p>
<blockquote>
<div><p>In this mode, the remarks and the metadata are serialized separately. The
client is responsible for parsing the metadata first, then use the metadata
to correctly parse the remarks.</p>
</div></blockquote>
<p><code class="docutils literal notranslate"><span class="pre">Standalone</span></code></p>
<blockquote>
<div><p>In this mode, the remarks and the metadata are serialized to the same
stream. The metadata will always come before the remarks.</p>
<p>The compiler does not support emitting standalone remarks. This mode is
more suited for post-processing tools like linkers, that can merge the
remarks for one whole project.</p>
</div></blockquote>
</div>
<div class="section" id="yaml-remarks">
<span id="yamlremarks"></span><h2><a class="toc-backref" href="#id6">YAML remarks</a><a class="headerlink" href="#yaml-remarks" title="Permalink to this headline">¶</a></h2>
<p>A typical remark serialized to YAML looks like this:</p>
<div class="highlight-yaml notranslate"><div class="highlight"><pre><span></span><span class="nn">---</span> <span class="kt">!<TYPE></span>
<span class="nt">Pass</span><span class="p">:</span> <span class="l l-Scalar l-Scalar-Plain"><pass></span>
<span class="nt">Name</span><span class="p">:</span> <span class="l l-Scalar l-Scalar-Plain"><name></span>
<span class="nt">DebugLoc</span><span class="p">:</span> <span class="p p-Indicator">{</span><span class="nt"> File</span><span class="p">:</span> <span class="nv"><file></span><span class="p p-Indicator">,</span><span class="nt"> Line</span><span class="p">:</span> <span class="nv"><line></span><span class="p p-Indicator">,</span><span class="nt"> Column</span><span class="p">:</span> <span class="nv"><column></span> <span class="p p-Indicator">}</span>
<span class="nt">Function</span><span class="p">:</span> <span class="l l-Scalar l-Scalar-Plain"><function></span>
<span class="nt">Hotness</span><span class="p">:</span> <span class="l l-Scalar l-Scalar-Plain"><hotness></span>
<span class="nt">Args</span><span class="p">:</span>
<span class="p p-Indicator">-</span> <span class="nt"><key></span><span class="p">:</span> <span class="l l-Scalar l-Scalar-Plain"><value></span>
<span class="nt">DebugLoc</span><span class="p">:</span> <span class="p p-Indicator">{</span><span class="nt"> File</span><span class="p">:</span> <span class="nv"><arg-file></span><span class="p p-Indicator">,</span><span class="nt"> Line</span><span class="p">:</span> <span class="nv"><arg-line></span><span class="p p-Indicator">,</span><span class="nt"> Column</span><span class="p">:</span> <span class="nv"><arg-column></span> <span class="p p-Indicator">}</span>
</pre></div>
</div>
<p>The following entries are mandatory:</p>
<ul class="simple">
<li><p><code class="docutils literal notranslate"><span class="pre"><TYPE></span></code>: can be <code class="docutils literal notranslate"><span class="pre">Passed</span></code>, <code class="docutils literal notranslate"><span class="pre">Missed</span></code>, <code class="docutils literal notranslate"><span class="pre">Analysis</span></code>,
<code class="docutils literal notranslate"><span class="pre">AnalysisFPCommute</span></code>, <code class="docutils literal notranslate"><span class="pre">AnalysisAliasing</span></code>, <code class="docutils literal notranslate"><span class="pre">Failure</span></code>.</p></li>
<li><p><code class="docutils literal notranslate"><span class="pre"><pass></span></code>: the name of the pass that emitted this remark.</p></li>
<li><p><code class="docutils literal notranslate"><span class="pre"><name></span></code>: the name of the remark coming from <code class="docutils literal notranslate"><span class="pre"><pass></span></code>.</p></li>
<li><p><code class="docutils literal notranslate"><span class="pre"><function></span></code>: the mangled name of the function.</p></li>
</ul>
<p>If a <code class="docutils literal notranslate"><span class="pre">DebugLoc</span></code> entry is specified, the following fields are required:</p>
<ul class="simple">
<li><p><code class="docutils literal notranslate"><span class="pre"><file></span></code></p></li>
<li><p><code class="docutils literal notranslate"><span class="pre"><line></span></code></p></li>
<li><p><code class="docutils literal notranslate"><span class="pre"><column></span></code></p></li>
</ul>
<p>If an <code class="docutils literal notranslate"><span class="pre">arg</span></code> entry is specified, the following fields are required:</p>
<ul class="simple">
<li><p><code class="docutils literal notranslate"><span class="pre"><key></span></code></p></li>
<li><p><code class="docutils literal notranslate"><span class="pre"><value></span></code></p></li>
</ul>
<p>If a <code class="docutils literal notranslate"><span class="pre">DebugLoc</span></code> entry is specified within an <code class="docutils literal notranslate"><span class="pre">arg</span></code> entry, the following
fields are required:</p>
<ul class="simple">
<li><p><code class="docutils literal notranslate"><span class="pre"><arg-file></span></code></p></li>
<li><p><code class="docutils literal notranslate"><span class="pre"><arg-line></span></code></p></li>
<li><p><code class="docutils literal notranslate"><span class="pre"><arg-column></span></code></p></li>
</ul>
<div class="section" id="yaml-with-a-string-table">
<span id="yamlstrtabremarks"></span><h3><a class="toc-backref" href="#id7">YAML with a string table</a><a class="headerlink" href="#yaml-with-a-string-table" title="Permalink to this headline">¶</a></h3>
<p>The YAML serialization supports the usage of a string table by using the
<code class="docutils literal notranslate"><span class="pre">yaml-strtab</span></code> format.</p>
<p>This format replaces strings in the YAML output with integers representing the
index in the string table that can be provided separately through metadata.</p>
<p>The following entries can take advantage of the string table while respecting
YAML rules:</p>
<ul class="simple">
<li><p><code class="docutils literal notranslate"><span class="pre"><pass></span></code></p></li>
<li><p><code class="docutils literal notranslate"><span class="pre"><name></span></code></p></li>
<li><p><code class="docutils literal notranslate"><span class="pre"><function></span></code></p></li>
<li><p><code class="docutils literal notranslate"><span class="pre"><file></span></code></p></li>
<li><p><code class="docutils literal notranslate"><span class="pre"><value></span></code></p></li>
<li><p><code class="docutils literal notranslate"><span class="pre"><arg-file></span></code></p></li>
</ul>
<p>Currently, none of the tools in <a class="reference internal" href="#optviewer"><span class="std std-ref">the opt-viewer directory</span></a>
support this format.</p>
</div>
<div class="section" id="yaml-metadata">
<span id="optviewer"></span><h3><a class="toc-backref" href="#id8">YAML metadata</a><a class="headerlink" href="#yaml-metadata" title="Permalink to this headline">¶</a></h3>
<p>The metadata used together with the YAML format is:</p>
<ul class="simple">
<li><p>a magic number: “REMARKS\0”</p></li>
<li><p>the version number: a little-endian uint64_t</p></li>
<li><p>the total size of the string table (the size itself excluded):
little-endian uint64_t</p></li>
<li><p>a list of null-terminated strings</p></li>
</ul>
<p>Optional:</p>
<ul class="simple">
<li><p>the absolute file path to the serialized remark diagnostics: a
null-terminated string.</p></li>
</ul>
<p>When the metadata is serialized separately from the remarks, the file path
should be present and point to the file where the remarks are serialized to.</p>
<p>In case the metadata only acts as a header to the remarks, the file path can be
omitted.</p>
</div>
</div>
<div class="section" id="llvm-bitstream-remarks">
<span id="bitstreamremarks"></span><h2><a class="toc-backref" href="#id9">LLVM bitstream remarks</a><a class="headerlink" href="#llvm-bitstream-remarks" title="Permalink to this headline">¶</a></h2>
<p>This format is using <a class="reference internal" href="BitCodeFormat.html"><span class="doc">LLVM bitstream</span></a> to serialize remarks
and their associated metadata.</p>
<p>A bitstream remark stream can be identified by the magic number <code class="docutils literal notranslate"><span class="pre">"RMRK"</span></code> that
is placed at the very beginning.</p>
<p>The format for serializing remarks is composed of two different block types:</p>
<div class="section" id="meta-block">
<span id="bitstreamremarksmetablock"></span><h3><a class="toc-backref" href="#id10">META_BLOCK</a><a class="headerlink" href="#meta-block" title="Permalink to this headline">¶</a></h3>
<p>The block providing information about the rest of the content in the stream.</p>
<p>Exactly one block is expected. Having multiple metadata blocks is an error.</p>
<p>This block can contain the following records:</p>
<p id="bitstreamremarksrecordmetacontainerinfo"><code class="docutils literal notranslate"><span class="pre">RECORD_META_CONTAINER_INFO</span></code></p>
<blockquote>
<div><p>The container version and type.</p>
<p>Version: u32</p>
<p>Type: u2</p>
</div></blockquote>
<p id="bitstreamremarksrecordmetaremarkversion"><code class="docutils literal notranslate"><span class="pre">RECORD_META_REMARK_VERSION</span></code></p>
<blockquote>
<div><p>The version of the remark entries. This can change independently from the
container version.</p>
<p>Version: u32</p>
</div></blockquote>
<p id="bitstreamremarksrecordmetastrtab"><code class="docutils literal notranslate"><span class="pre">RECORD_META_STRTAB</span></code></p>
<blockquote>
<div><p>The string table used by the remark entries. The format of the string table
is a sequence of strings separated by <code class="docutils literal notranslate"><span class="pre">\0</span></code>.</p>
</div></blockquote>
<p id="bitstreamremarksrecordmetaexternalfile"><code class="docutils literal notranslate"><span class="pre">RECORD_META_EXTERNAL_FILE</span></code></p>
<blockquote>
<div><p>The external remark file path that contains the remark blocks associated
with this metadata. This is an absolute path.</p>
</div></blockquote>
</div>
<div class="section" id="remark-block">
<span id="bitstreamremarksremarkblock"></span><h3><a class="toc-backref" href="#id11">REMARK_BLOCK</a><a class="headerlink" href="#remark-block" title="Permalink to this headline">¶</a></h3>
<p>The block describing a remark entry.</p>
<p>0 or more blocks per file are allowed. Each block will depend on the
<a class="reference internal" href="#bitstreamremarksmetablock"><span class="std std-ref">META_BLOCK</span></a> in order to be parsed correctly.</p>
<p>This block can contain the following records:</p>
<p><code class="docutils literal notranslate"><span class="pre">RECORD_REMARK_HEADER</span></code></p>
<blockquote>
<div><p>The header of the remark. This contains all the mandatory information about
a remark.</p>
<table class="docutils align-default">
<colgroup>
<col style="width: 36%" />
<col style="width: 64%" />
</colgroup>
<tbody>
<tr class="row-odd"><td><p>Type</p></td>
<td><p>u3</p></td>
</tr>
<tr class="row-even"><td><p>Remark name</p></td>
<td><p>VBR6 (string table index)</p></td>
</tr>
<tr class="row-odd"><td><p>Pass name</p></td>
<td><p>VBR6 (string table index)</p></td>
</tr>
<tr class="row-even"><td><p>Function name</p></td>
<td><p>VBR6 (string table index)</p></td>
</tr>
</tbody>
</table>
</div></blockquote>
<p><code class="docutils literal notranslate"><span class="pre">RECORD_REMARK_DEBUG_LOC</span></code></p>
<blockquote>
<div><p>The source location for the corresponding remark. This record is optional.</p>
<table class="docutils align-default">
<colgroup>
<col style="width: 23%" />
<col style="width: 77%" />
</colgroup>
<tbody>
<tr class="row-odd"><td><p>File</p></td>
<td><p>VBR7 (string table index)</p></td>
</tr>
<tr class="row-even"><td><p>Line</p></td>
<td><p>u32</p></td>
</tr>
<tr class="row-odd"><td><p>Column</p></td>
<td><p>u32</p></td>
</tr>
</tbody>
</table>
</div></blockquote>
<p><code class="docutils literal notranslate"><span class="pre">RECORD_REMARK_HOTNESS</span></code></p>
<blockquote>
<div><p>The hotness of the remark. This record is optional.</p>
<table class="docutils align-default">
<colgroup>
<col style="width: 42%" />
<col style="width: 58%" />
</colgroup>
<tbody>
<tr class="row-odd"><td colspan="2"><p>Hotness | VBR8 (string table index)</p></td>
</tr>
</tbody>
</table>
</div></blockquote>
<p><code class="docutils literal notranslate"><span class="pre">RECORD_REMARK_ARG_WITH_DEBUGLOC</span></code></p>
<blockquote>
<div><p>A remark argument with an associated debug location.</p>
<table class="docutils align-default">
<colgroup>
<col style="width: 23%" />
<col style="width: 77%" />
</colgroup>
<tbody>
<tr class="row-odd"><td><p>Key</p></td>
<td><p>VBR7 (string table index)</p></td>
</tr>
<tr class="row-even"><td><p>Value</p></td>
<td><p>VBR7 (string table index)</p></td>
</tr>
<tr class="row-odd"><td><p>File</p></td>
<td><p>VBR7 (string table index)</p></td>
</tr>
<tr class="row-even"><td><p>Line</p></td>
<td><p>u32</p></td>
</tr>
<tr class="row-odd"><td><p>Column</p></td>
<td><p>u32</p></td>
</tr>
</tbody>
</table>
</div></blockquote>
<p><code class="docutils literal notranslate"><span class="pre">RECORD_REMARK_ARG_WITHOUT_DEBUGLOC</span></code></p>
<blockquote>
<div><p>A remark argument with an associated debug location.</p>
<table class="docutils align-default">
<colgroup>
<col style="width: 23%" />
<col style="width: 77%" />
</colgroup>
<tbody>
<tr class="row-odd"><td><p>Key</p></td>
<td><p>VBR7 (string table index)</p></td>
</tr>
<tr class="row-even"><td><p>Value</p></td>
<td><p>VBR7 (string table index)</p></td>
</tr>
</tbody>
</table>
</div></blockquote>
</div>
<div class="section" id="the-remark-container">
<h3><a class="toc-backref" href="#id12">The remark container</a><a class="headerlink" href="#the-remark-container" title="Permalink to this headline">¶</a></h3>
<p>Bitstream remarks are designed to be used in two different modes:</p>
<p><code class="docutils literal notranslate"><span class="pre">The</span> <span class="pre">separate</span> <span class="pre">mode</span></code></p>
<blockquote>
<div><p>The separate mode is the mode that is typically used during compilation. It
provides a way to serialize the remark entries to a stream while some
metadata is kept in memory to be emitted in the product of the compilation
(typically, an object file).</p>
</div></blockquote>
<p><code class="docutils literal notranslate"><span class="pre">The</span> <span class="pre">standalone</span> <span class="pre">mode</span></code></p>
<blockquote>
<div><p>The standalone mode is typically stored and used after the distribution of
a program. It contains all the information that allows the parsing of all
the remarks without having any external dependencies.</p>
</div></blockquote>
<p>In order to support multiple modes, the format introduces the concept of a
bitstream remark container type.</p>
<p id="bitstreamremarksseparateremarksmeta"><code class="docutils literal notranslate"><span class="pre">SeparateRemarksMeta:</span> <span class="pre">the</span> <span class="pre">metadata</span> <span class="pre">emitted</span> <span class="pre">separately</span></code></p>
<blockquote>
<div><p>This container type expects only a <a class="reference internal" href="#bitstreamremarksmetablock"><span class="std std-ref">META_BLOCK</span></a> containing only:</p>
<ul class="simple">
<li><p><a class="reference internal" href="#bitstreamremarksrecordmetacontainerinfo"><span class="std std-ref">RECORD_META_CONTAINER_INFO</span></a></p></li>
<li><p><a class="reference internal" href="#bitstreamremarksrecordmetastrtab"><span class="std std-ref">RECORD_META_STRTAB</span></a></p></li>
<li><p><a class="reference internal" href="#bitstreamremarksrecordmetaexternalfile"><span class="std std-ref">RECORD_META_EXTERNAL_FILE</span></a></p></li>
</ul>
<p>Typically, this is emitted in a section in the object files, allowing
clients to retrieve remarks and their associated metadata directly from
intermediate products.</p>
</div></blockquote>
<p><code class="docutils literal notranslate"><span class="pre">SeparateRemarksFile:</span> <span class="pre">the</span> <span class="pre">remark</span> <span class="pre">entries</span> <span class="pre">emitted</span> <span class="pre">separately</span></code></p>
<blockquote>
<div><p>This container type expects only a <a class="reference internal" href="#bitstreamremarksmetablock"><span class="std std-ref">META_BLOCK</span></a> containing only:</p>
<ul class="simple">
<li><p><a class="reference internal" href="#bitstreamremarksrecordmetacontainerinfo"><span class="std std-ref">RECORD_META_CONTAINER_INFO</span></a></p></li>
<li><p><a class="reference internal" href="#bitstreamremarksrecordmetaremarkversion"><span class="std std-ref">RECORD_META_REMARK_VERSION</span></a></p></li>
</ul>
<p>This container type expects 0 or more <a class="reference internal" href="#bitstreamremarksremarkblock"><span class="std std-ref">REMARK_BLOCK</span></a>.</p>
<p>Typically, this is emitted in a side-file alongside an object file, and is
made to be able to stream to without increasing the memory consumption of
the compiler. This is referenced by the <a class="reference internal" href="#bitstreamremarksrecordmetaexternalfile"><span class="std std-ref">RECORD_META_EXTERNAL_FILE</span></a> entry in the
<a class="reference internal" href="#bitstreamremarksseparateremarksmeta"><span class="std std-ref">SeparateRemarksMeta</span></a> container.</p>
</div></blockquote>
<p>When the parser tries to parse a container that contains the metadata for the
separate remarks, it should parse the version and type, then keep the string
table in memory while opening the external file, validating its metadata and
parsing the remark entries.</p>
<p>The container versions from the separate container should match in order to
have a well-formed file.</p>
<p><code class="docutils literal notranslate"><span class="pre">Standalone:</span> <span class="pre">the</span> <span class="pre">metadata</span> <span class="pre">and</span> <span class="pre">the</span> <span class="pre">remark</span> <span class="pre">entries</span> <span class="pre">emitted</span> <span class="pre">together</span></code></p>
<blockquote>
<div><p>This container type expects only a <a class="reference internal" href="#bitstreamremarksmetablock"><span class="std std-ref">META_BLOCK</span></a> containing only:</p>
<ul class="simple">
<li><p><a class="reference internal" href="#bitstreamremarksrecordmetacontainerinfo"><span class="std std-ref">RECORD_META_CONTAINER_INFO</span></a></p></li>
<li><p><a class="reference internal" href="#bitstreamremarksrecordmetaremarkversion"><span class="std std-ref">RECORD_META_REMARK_VERSION</span></a></p></li>
<li><p><a class="reference internal" href="#bitstreamremarksrecordmetastrtab"><span class="std std-ref">RECORD_META_STRTAB</span></a></p></li>
</ul>
<p>This container type expects 0 or more <a class="reference internal" href="#bitstreamremarksremarkblock"><span class="std std-ref">REMARK_BLOCK</span></a>.</p>
</div></blockquote>
<p>A complete output of <strong class="program">llvm-bcanalyzer</strong> on the different container types:</p>
<p><code class="docutils literal notranslate"><span class="pre">SeparateRemarksMeta</span></code></p>
<div class="highlight-none notranslate"><div class="highlight"><pre><span></span><BLOCKINFO_BLOCK/>
<Meta BlockID=8 NumWords=13 BlockCodeSize=3>
<Container info codeid=1 abbrevid=4 op0=5 op1=0/>
<String table codeid=3 abbrevid=5/> blob data = 'pass\\x00key\\x00value\\x00'
<External File codeid=4 abbrevid=6/> blob data = '/path/to/file/name'
</Meta>
</pre></div>
</div>
<p><code class="docutils literal notranslate"><span class="pre">SeparateRemarksFile</span></code></p>
<div class="highlight-none notranslate"><div class="highlight"><pre><span></span><BLOCKINFO_BLOCK/>
<Meta BlockID=8 NumWords=3 BlockCodeSize=3>
<Container info codeid=1 abbrevid=4 op0=0 op1=1/>
<Remark version codeid=2 abbrevid=5 op0=0/>
</Meta>
<Remark BlockID=9 NumWords=8 BlockCodeSize=4>
<Remark header codeid=5 abbrevid=4 op0=2 op1=0 op2=1 op3=2/>
<Remark debug location codeid=6 abbrevid=5 op0=3 op1=99 op2=55/>
<Remark hotness codeid=7 abbrevid=6 op0=999999999/>
<Argument with debug location codeid=8 abbrevid=7 op0=4 op1=5 op2=6 op3=11 op4=66/>
</Remark>
</pre></div>
</div>
<p><code class="docutils literal notranslate"><span class="pre">Standalone</span></code></p>
<div class="highlight-none notranslate"><div class="highlight"><pre><span></span><BLOCKINFO_BLOCK/>
<Meta BlockID=8 NumWords=15 BlockCodeSize=3>
<Container info codeid=1 abbrevid=4 op0=5 op1=2/>
<Remark version codeid=2 abbrevid=5 op0=30/>
<String table codeid=3 abbrevid=6/> blob data = 'pass\\x00remark\\x00function\\x00path\\x00key\\x00value\\x00argpath\\x00'
</Meta>
<Remark BlockID=9 NumWords=8 BlockCodeSize=4>
<Remark header codeid=5 abbrevid=4 op0=2 op1=1 op2=0 op3=2/>
<Remark debug location codeid=6 abbrevid=5 op0=3 op1=99 op2=55/>
<Remark hotness codeid=7 abbrevid=6 op0=999999999/>
<Argument with debug location codeid=8 abbrevid=7 op0=4 op1=5 op2=6 op3=11 op4=66/>
</Remark>
</pre></div>
</div>
</div>
</div>
<div class="section" id="opt-viewer">
<h2><a class="toc-backref" href="#id13">opt-viewer</a><a class="headerlink" href="#opt-viewer" title="Permalink to this headline">¶</a></h2>
<p>The <code class="docutils literal notranslate"><span class="pre">opt-viewer</span></code> directory contains a collection of tools that visualize and
summarize serialized remarks.</p>
<p>The tools only support the <code class="docutils literal notranslate"><span class="pre">yaml</span></code> format.</p>
<div class="section" id="opt-viewer-py">
<span id="optviewerpy"></span><h3><a class="toc-backref" href="#id14">opt-viewer.py</a><a class="headerlink" href="#opt-viewer-py" title="Permalink to this headline">¶</a></h3>
<p>Output a HTML page which gives visual feedback on compiler interactions with
your program.</p>
<blockquote>
<div><dl class="field-list simple">
<dt class="field-odd">Examples</dt>
<dd class="field-odd"><p></p></dd>
</dl>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span>$ opt-viewer.py my_yaml_file.opt.yaml
</pre></div>
</div>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span>$ opt-viewer.py my_build_dir/
</pre></div>
</div>
</div></blockquote>
</div>
<div class="section" id="opt-stats-py">
<h3><a class="toc-backref" href="#id15">opt-stats.py</a><a class="headerlink" href="#opt-stats-py" title="Permalink to this headline">¶</a></h3>
<p>Output statistics about the optimization remarks in the input set.</p>
<blockquote>
<div><dl class="field-list simple">
<dt class="field-odd">Example</dt>
<dd class="field-odd"><p></p></dd>
</dl>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span>$ opt-stats.py my_yaml_file.opt.yaml
Total number of remarks 3
Top 10 remarks by pass:
inline 33%
asm-printer 33%
prologepilog 33%
Top 10 remarks:
asm-printer/InstructionCount 33%
inline/NoDefinition 33%
prologepilog/StackSize 33%
</pre></div>
</div>
</div></blockquote>
</div>
<div class="section" id="opt-diff-py">
<h3><a class="toc-backref" href="#id16">opt-diff.py</a><a class="headerlink" href="#opt-diff-py" title="Permalink to this headline">¶</a></h3>
<p>Produce a new YAML file which contains all of the changes in optimizations
between two YAML files.</p>
<p>Typically, this tool should be used to do diffs between:</p>
<ul class="simple">
<li><p>new compiler + fixed source vs old compiler + fixed source</p></li>
<li><p>fixed compiler + new source vs fixed compiler + old source</p></li>
</ul>
<p>This diff file can be displayed using <a class="reference internal" href="#optviewerpy"><span class="std std-ref">opt-viewer.py</span></a>.</p>
<blockquote>
<div><dl class="field-list simple">
<dt class="field-odd">Example</dt>
<dd class="field-odd"><p></p></dd>
</dl>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span>$ opt-diff.py my_opt_yaml1.opt.yaml my_opt_yaml2.opt.yaml -o my_opt_diff.opt.yaml
$ opt-viewer.py my_opt_diff.opt.yaml
</pre></div>
</div>
</div></blockquote>
</div>
</div>
<div class="section" id="emitting-remark-diagnostics-in-the-object-file">
<span id="remarkssection"></span><h2><a class="toc-backref" href="#id17">Emitting remark diagnostics in the object file</a><a class="headerlink" href="#emitting-remark-diagnostics-in-the-object-file" title="Permalink to this headline">¶</a></h2>
<p>A section containing metadata on remark diagnostics will be emitted for the
following formats:</p>
<ul class="simple">
<li><p><code class="docutils literal notranslate"><span class="pre">yaml-strtab</span></code></p></li>
<li><p><code class="docutils literal notranslate"><span class="pre">bitstream</span></code></p></li>
</ul>
<p>This can be overridden by using the flag <code class="docutils literal notranslate"><span class="pre">-remarks-section=<bool></span></code>.</p>
<p>The section is named:</p>
<ul class="simple">
<li><p><code class="docutils literal notranslate"><span class="pre">__LLVM,__remarks</span></code> (MachO)</p></li>
</ul>
</div>
<div class="section" id="c-api">
<h2><a class="toc-backref" href="#id18">C API</a><a class="headerlink" href="#c-api" title="Permalink to this headline">¶</a></h2>
<p>LLVM provides a library that can be used to parse remarks through a shared
library named <code class="docutils literal notranslate"><span class="pre">libRemarks</span></code>.</p>
<p>The typical usage through the C API is like the following:</p>
<div class="highlight-c notranslate"><div class="highlight"><pre><span></span><span class="n">LLVMRemarkParserRef</span> <span class="n">Parser</span> <span class="o">=</span> <span class="n">LLVMRemarkParserCreateYAML</span><span class="p">(</span><span class="n">Buf</span><span class="p">,</span> <span class="n">Size</span><span class="p">);</span>
<span class="n">LLVMRemarkEntryRef</span> <span class="n">Remark</span> <span class="o">=</span> <span class="nb">NULL</span><span class="p">;</span>
<span class="k">while</span> <span class="p">((</span><span class="n">Remark</span> <span class="o">=</span> <span class="n">LLVMRemarkParserGetNext</span><span class="p">(</span><span class="n">Parser</span><span class="p">)))</span> <span class="p">{</span>
<span class="c1">// use Remark</span>
<span class="n">LLVMRemarkEntryDispose</span><span class="p">(</span><span class="n">Remark</span><span class="p">);</span> <span class="c1">// Release memory.</span>
<span class="p">}</span>
<span class="kt">bool</span> <span class="n">HasError</span> <span class="o">=</span> <span class="n">LLVMRemarkParserHasError</span><span class="p">(</span><span class="n">Parser</span><span class="p">);</span>
<span class="n">LLVMRemarkParserDispose</span><span class="p">(</span><span class="n">Parser</span><span class="p">);</span>
</pre></div>
</div>
</div>
<div class="section" id="remark-streamers">
<h2><a class="toc-backref" href="#id19">Remark streamers</a><a class="headerlink" href="#remark-streamers" title="Permalink to this headline">¶</a></h2>
<p>The <code class="docutils literal notranslate"><span class="pre">RemarkStreamer</span></code> interface is used to unify the serialization
capabilities of remarks across all the components that can generate remarks.</p>
<p>All remark serialization should go through the main remark streamer, the
<code class="docutils literal notranslate"><span class="pre">llvm::remarks::RemarkStreamer</span></code> set up in the <code class="docutils literal notranslate"><span class="pre">LLVMContext</span></code>. The interface
takes remark objects converted to <code class="docutils literal notranslate"><span class="pre">llvm::remarks::Remark</span></code>, and takes care of
serializing it to the requested format, using the requested type of metadata,
etc.</p>
<p>Typically, a specialized remark streamer will hold a reference to the one set
up in the <code class="docutils literal notranslate"><span class="pre">LLVMContext</span></code>, and will operate on its own type of diagnostics.</p>
<p>For example, LLVM IR passes will emit <code class="docutils literal notranslate"><span class="pre">llvm::DiagnosticInfoOptimization*</span></code>
that get converted to <code class="docutils literal notranslate"><span class="pre">llvm::remarks::Remark</span></code> objects. Then, clang could set
up its own specialized remark streamer that takes <code class="docutils literal notranslate"><span class="pre">clang::Diagnostic</span></code>
objects. This can allow various components of the frontend to emit remarks
using the same techniques as the LLVM remarks.</p>
<p>This gives us the following advantages:</p>
<ul class="simple">
<li><p>Composition: during the compilation pipeline, multiple components can set up
their specialized remark streamers that all emit remarks through the same
main streamer.</p></li>
<li><p>Re-using the remark infrastructure in <code class="docutils literal notranslate"><span class="pre">lib/Remarks</span></code>.</p></li>
<li><p>Using the same file and format for the remark emitters created throughout the
compilation.</p></li>
</ul>
<p>at the cost of an extra layer of abstraction.</p>
</div>
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