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<div class="section" id="how-to-add-a-constrained-floating-point-intrinsic">
<h1>How To Add A Constrained Floating-Point Intrinsic<a class="headerlink" href="#how-to-add-a-constrained-floating-point-intrinsic" title="Permalink to this headline">¶</a></h1>
<div class="contents local topic" id="contents">
<ul class="simple">
<li><p><a class="reference internal" href="#add-the-intrinsic" id="id1">Add the intrinsic</a></p></li>
<li><p><a class="reference internal" href="#add-selectiondag-node-types" id="id2">Add SelectionDAG node types</a></p></li>
<li><p><a class="reference internal" href="#update-mappings" id="id3">Update mappings</a></p></li>
<li><p><a class="reference internal" href="#update-ir-components" id="id4">Update IR components</a></p></li>
<li><p><a class="reference internal" href="#update-selector-components" id="id5">Update Selector components</a></p>
<ul>
<li><p><a class="reference internal" href="#building-the-selectiondag" id="id6">Building the SelectionDAG</a></p></li>
</ul>
</li>
<li><p><a class="reference internal" href="#add-documentation-and-tests" id="id7">Add documentation and tests</a></p></li>
</ul>
</div>
<div class="admonition warning">
<p class="admonition-title">Warning</p>
<p>This is a work in progress.</p>
</div>
<div class="section" id="add-the-intrinsic">
<h2><a class="toc-backref" href="#id1">Add the intrinsic</a><a class="headerlink" href="#add-the-intrinsic" title="Permalink to this headline">¶</a></h2>
<p>Multiple files need to be updated when adding a new constrained intrinsic.</p>
<p>Add the new intrinsic to the table of intrinsics:</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">include</span><span class="o">/</span><span class="n">llvm</span><span class="o">/</span><span class="n">IR</span><span class="o">/</span><span class="n">Intrinsics</span><span class="o">.</span><span class="n">td</span>
</pre></div>
</div>
</div>
<div class="section" id="add-selectiondag-node-types">
<h2><a class="toc-backref" href="#id2">Add SelectionDAG node types</a><a class="headerlink" href="#add-selectiondag-node-types" title="Permalink to this headline">¶</a></h2>
<p>Add the new STRICT version of the node type to the ISD::NodeType enum:</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">include</span><span class="o">/</span><span class="n">llvm</span><span class="o">/</span><span class="n">CodeGen</span><span class="o">/</span><span class="n">ISDOpcodes</span><span class="o">.</span><span class="n">h</span>
</pre></div>
</div>
<p>Strict version name must be a concatenation of prefix <code class="docutils literal notranslate"><span class="pre">STRICT_</span></code> and the name
of corresponding non-strict node name. For instance, strict version of the
node FADD must be STRICT_FADD.</p>
</div>
<div class="section" id="update-mappings">
<h2><a class="toc-backref" href="#id3">Update mappings</a><a class="headerlink" href="#update-mappings" title="Permalink to this headline">¶</a></h2>
<p>Add new record to the mapping of instructions to constrained intrinsic and
DAG nodes:</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">include</span><span class="o">/</span><span class="n">llvm</span><span class="o">/</span><span class="n">IR</span><span class="o">/</span><span class="n">ConstrainedOps</span><span class="o">.</span><span class="k">def</span>
</pre></div>
</div>
<p>Follow instructions provided in this file.</p>
</div>
<div class="section" id="update-ir-components">
<h2><a class="toc-backref" href="#id4">Update IR components</a><a class="headerlink" href="#update-ir-components" title="Permalink to this headline">¶</a></h2>
<p>Update the IR verifier:</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">lib</span><span class="o">/</span><span class="n">IR</span><span class="o">/</span><span class="n">Verifier</span><span class="o">.</span><span class="n">cpp</span>
</pre></div>
</div>
</div>
<div class="section" id="update-selector-components">
<h2><a class="toc-backref" href="#id5">Update Selector components</a><a class="headerlink" href="#update-selector-components" title="Permalink to this headline">¶</a></h2>
<div class="section" id="building-the-selectiondag">
<h3><a class="toc-backref" href="#id6">Building the SelectionDAG</a><a class="headerlink" href="#building-the-selectiondag" title="Permalink to this headline">¶</a></h3>
<p>The function SelectionDAGBuilder::visitConstrainedFPIntrinsic builds DAG nodes
using mappings specified in ConstrainedOps.def. If however this default build is
not sufficient, the build can be modified, see how it is implemented for
STRICT_FP_ROUND. The new STRICT node will eventually be converted
to the matching non-STRICT node. For this reason it should have the same
operands and values as the non-STRICT version but should also use the chain.
This makes subsequent sharing of code for STRICT and non-STRICT code paths
easier:</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">lib</span><span class="o">/</span><span class="n">CodeGen</span><span class="o">/</span><span class="n">SelectionDAG</span><span class="o">/</span><span class="n">SelectionDAGBuilder</span><span class="o">.</span><span class="n">cpp</span>
</pre></div>
</div>
<p>Most of the STRICT nodes get legalized the same as their matching non-STRICT
counterparts. A new STRICT node with this property must get added to the
switch in SelectionDAGLegalize::LegalizeOp().:</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">lib</span><span class="o">/</span><span class="n">CodeGen</span><span class="o">/</span><span class="n">SelectionDAG</span><span class="o">/</span><span class="n">LegalizeDAG</span><span class="o">.</span><span class="n">cpp</span>
</pre></div>
</div>
<p>Other parts of the legalizer may need to be updated as well. Look for
places where the non-STRICT counterpart is legalized and update as needed.
Be careful of the chain since STRICT nodes use it but their counterparts
often don’t.</p>
<p>The code to do the conversion or mutation of the STRICT node to a non-STRICT
version of the node happens in SelectionDAG::mutateStrictFPToFP(). In most cases
the function can do the conversion using information from ConstrainedOps.def. Be
careful updating this function since some nodes have the same return type
as their input operand, but some are different. Both of these cases must
be properly handled:</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">lib</span><span class="o">/</span><span class="n">CodeGen</span><span class="o">/</span><span class="n">SelectionDAG</span><span class="o">/</span><span class="n">SelectionDAG</span><span class="o">.</span><span class="n">cpp</span>
</pre></div>
</div>
<p>Whether the mutation may happens or not, depends on how the new node has been
registered in TargetLoweringBase::initActions(). By default all strict nodes are
registered with Expand action:</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">lib</span><span class="o">/</span><span class="n">CodeGen</span><span class="o">/</span><span class="n">TargetLoweringBase</span><span class="o">.</span><span class="n">cpp</span>
</pre></div>
</div>
<p>To make debug logs readable it is helpful to update the SelectionDAG’s
debug logger::</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">lib</span><span class="o">/</span><span class="n">CodeGen</span><span class="o">/</span><span class="n">SelectionDAG</span><span class="o">/</span><span class="n">SelectionDAGDumper</span><span class="o">.</span><span class="n">cpp</span>
</pre></div>
</div>
</div>
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<div class="section" id="add-documentation-and-tests">
<h2><a class="toc-backref" href="#id7">Add documentation and tests</a><a class="headerlink" href="#add-documentation-and-tests" title="Permalink to this headline">¶</a></h2>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="n">docs</span><span class="o">/</span><span class="n">LangRef</span><span class="o">.</span><span class="n">rst</span>
</pre></div>
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