<div dir="ltr"><div class="markdown-here-wrapper" style=""><p style="margin:0px 0px 1.2em!important">TableGen, as a DSL language, is made up of records. Every <code style="font-size:0.85em;font-family:Consolas,Inconsolata,Courier,monospace;margin:0px 0.15em;padding:0px 0.3em;white-space:pre-wrap;border:1px solid rgb(234,234,234);border-radius:3px;display:inline;background-color:rgb(248,248,248)">def</code> corresponds to a record. For example, TableGen has a <code style="font-size:0.85em;font-family:Consolas,Inconsolata,Courier,monospace;margin:0px 0.15em;padding:0px 0.3em;white-space:pre-wrap;border:1px solid rgb(234,234,234);border-radius:3px;display:inline;background-color:rgb(248,248,248)">class Register</code>, and your backend will define records by <code style="font-size:0.85em;font-family:Consolas,Inconsolata,Courier,monospace;margin:0px 0.15em;padding:0px 0.3em;white-space:pre-wrap;border:1px solid rgb(234,234,234);border-radius:3px;display:inline;background-color:rgb(248,248,248)">def GPR8 : Register<...></code>. You are correct in saying that the record definition is one of the <code style="font-size:0.85em;font-family:Consolas,Inconsolata,Courier,monospace;margin:0px 0.15em;padding:0px 0.3em;white-space:pre-wrap;border:1px solid rgb(234,234,234);border-radius:3px;display:inline;background-color:rgb(248,248,248)">SDNode</code> values. These correspond 1:1 to <a href="http://llvm.org/docs/doxygen/html/namespacellvm_1_1ISD.html#a22ea9cec080dd5f4f47ba234c2f59110"><code style="font-size:0.85em;font-family:Consolas,Inconsolata,Courier,monospace;margin:0px 0.15em;padding:0px 0.3em;white-space:pre-wrap;border:1px solid rgb(234,234,234);border-radius:3px;display:inline;background-color:rgb(248,248,248)">llvm::ISD::NodeType</code></a>.</p>
<p style="margin:0px 0px 1.2em!important"><code style="font-size:0.85em;font-family:Consolas,Inconsolata,Courier,monospace;margin:0px 0.15em;padding:0px 0.3em;white-space:pre-wrap;border:1px solid rgb(234,234,234);border-radius:3px;display:inline;background-color:rgb(248,248,248)">(DEF a, b)</code> corresponds to</p>
<pre style="font-size:0.85em;font-family:Consolas,Inconsolata,Courier,monospace;font-size:1em;line-height:1.2em;margin:1.2em 0px"><code style="font-size:0.85em;font-family:Consolas,Inconsolata,Courier,monospace;margin:0px 0.15em;padding:0px 0.3em;white-space:pre-wrap;border:1px solid rgb(234,234,234);border-radius:3px;display:inline;background-color:rgb(248,248,248);white-space:pre;overflow:auto;border-radius:3px;border:1px solid rgb(204,204,204);padding:0.5em 0.7em;display:block!important"> --------- a
/
DEF
\
----------b
</code></pre><p style="margin:0px 0px 1.2em!important">A more complicated example, regarding that <code style="font-size:0.85em;font-family:Consolas,Inconsolata,Courier,monospace;margin:0px 0.15em;padding:0px 0.3em;white-space:pre-wrap;border:1px solid rgb(234,234,234);border-radius:3px;display:inline;background-color:rgb(248,248,248)">a</code> and <code style="font-size:0.85em;font-family:Consolas,Inconsolata,Courier,monospace;margin:0px 0.15em;padding:0px 0.3em;white-space:pre-wrap;border:1px solid rgb(234,234,234);border-radius:3px;display:inline;background-color:rgb(248,248,248)">b</code> themselves can be nested DAGs.</p>
<pre style="font-size:0.85em;font-family:Consolas,Inconsolata,Courier,monospace;font-size:1em;line-height:1.2em;margin:1.2em 0px"><code style="font-size:0.85em;font-family:Consolas,Inconsolata,Courier,monospace;margin:0px 0.15em;padding:0px 0.3em;white-space:pre-wrap;border:1px solid rgb(234,234,234);border-radius:3px;display:inline;background-color:rgb(248,248,248);white-space:pre;overflow:auto;border-radius:3px;border:1px solid rgb(204,204,204);padding:0.5em 0.7em;display:block!important"> a
/
--------- add
/ \
/ b
DEF
\ c
\ /
---------- sub
\
d
</code></pre><p style="margin:0px 0px 1.2em!important">And so on and so fourth.</p>
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c3A7ICZuYnNwOyBkPC9kaXY+PGRpdiBzdHlsZT0iZm9udC1zaXplOiAxMi44cHg7Ij5gYGA8L2Rp
dj48ZGl2IHN0eWxlPSJmb250LXNpemU6IDEyLjhweDsiPjxicj48L2Rpdj48ZGl2IHN0eWxlPSJm
b250LXNpemU6IDEyLjhweDsiPkFuZCBzbyBvbiBhbmQgc28gZm91cnRoLjwvZGl2PjwvZGl2Pg==" style="height:0;width:0;max-height:0;max-width:0;overflow:hidden;font-size:0em;padding:0;margin:0"></div></div></div><div class="gmail_extra"><br><div class="gmail_quote">On Sat, Jan 30, 2016 at 8:54 AM, Rail Shafigulin <span dir="ltr"><<a href="mailto:rail@esenciatech.com" target="_blank">rail@esenciatech.com</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div dir="ltr"><br><div class="gmail_extra"><br><div class="gmail_quote"><span class="">On Fri, Jan 29, 2016 at 11:39 AM, Rail Shafigulin <span dir="ltr"><<a href="mailto:rail@esenciatech.com" target="_blank">rail@esenciatech.com</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"><div dir="ltr"><br><div class="gmail_extra"><br><div class="gmail_quote"><span>On Thu, Jan 28, 2016 at 8:34 PM, Dylan McKay <span dir="ltr"><<a href="mailto:dylanmckay34@gmail.com" target="_blank">dylanmckay34@gmail.com</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"><div dir="ltr">Try visualising the DAG like this.<div><br></div><div>```</div><div> ---- GPR:$rA</div><div> /</div><div>set GPR:$rd ---- add</div><div> \</div><div> ---- GPR:$rB</div><div>```</div><div><br></div><div>Each instruction forms a DAG with its operands being subnodes.</div><div><br></div><div>The core instruction selection logic just looks for the pattern `(set GPR:$rd, (add GPR:$rA, GPR:$rB))`. It then becomes a simple substitution. This is a DAG because there all nodes are directed and acyclic. <br></div></div></blockquote><div><br><br></div></span><div>Am I correct in my understanding that each node can either be a register or of type SDNode defined in TargetSelectionDAG.td? <br></div></div></div></div></blockquote><div><br></div></span><div>I should clarify. What I'm confused about is how exactly the DAG is defined. Here is what is says on <a href="http://llvm.org/docs/TableGen/LangIntro.html" target="_blank">llvm.org/docs/TableGen/LangIntro.html</a><br><dl><dt><tt><span>(DEF</span> <span>a,</span> <span>b)</span></tt></dt><dd>a dag value. The first element is required to be a record definition, the
remaining elements in the list may be arbitrary other values, including
nested <tt><span>`dag</span></tt>‘ values.</dd></dl>What is meant by a record definition? Is it a definition of type SDNode which are defined in TargetSelectionDAG.td?<br></div><div>What exactly does (DEF, a, b) represent in the graph?<br><br></div><div>Is it <br><br></div><div> --------- a<br></div><div> /<br></div><div>DEF<br></div><div> \<br> ----------b<br><br></div><div>or <br><br></div><div> --------a<br></div><div>/<br></div><div>-------- DEF<br>\<br></div><div> -------b<br><br></div><span class=""><div><br></div><div> <br></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"><div dir="ltr"><div class="gmail_extra"><div class="gmail_quote"><div></div><span><div><br></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"><div dir="ltr"><div></div></div><div class="gmail_extra"><br><div class="gmail_quote"><div><div>On Thu, Jan 28, 2016 at 7:33 PM, Rail Shafigulin via llvm-dev <span dir="ltr"><<a href="mailto:llvm-dev@lists.llvm.org" target="_blank">llvm-dev@lists.llvm.org</a>></span> wrote:<br></div></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"><div><div><div dir="ltr"><div><div>I'm confused about how to specify DAG patterns for a given instruction<br><br></div>Here is an example for my target<br><br>class ALU1_RR<bits<4> subOp, string asmstr, SDNode OpNode><br> : ALU_RR<subOp, asmstr,<br> [(set GPR:$rD, (OpNode (i32 GPR:$rA), (i32 GPR:$rB)))]>;<br><br>def ADD : ALU1_RR<0x0, "l.add", add>;<br><br></div>The set operation simply creates a list. The add operation creates a union. So at the end [(set GPR:$rD, (OpNode (i32 GPR:$rA), (i32 GPR:$rB)))] becomes a just a regular set. How come this is a DAG? I feel like I'm missing something. Would anyone be able to help with the explanation?<span><font color="#888888"><br><div><div><div><div><br>-- <br><div><div dir="ltr"><div><div dir="ltr"><div>Rail Shafigulin<br></div>Software Engineer <br>Esencia Technologies<br></div></div></div></div>
</div></div></div></div></font></span></div>
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<br></blockquote></div><br></div>
</blockquote></span></div><span><br><br clear="all"><br>-- <br><div><div dir="ltr"><div><div dir="ltr"><div>Rail Shafigulin<br></div>Software Engineer <br>Esencia Technologies<br></div></div></div></div>
</span></div></div>
</blockquote></span></div><span class=""><br><br clear="all"><br>-- <br><div><div dir="ltr"><div><div dir="ltr"><div>Rail Shafigulin<br></div>Software Engineer <br>Esencia Technologies<br></div></div></div></div>
</span></div></div>
</blockquote></div><br></div>