<div dir="ltr"><div class="gmail_default" style="font-family:arial,helvetica,sans-serif">Hi Peter,</div><div class="gmail_extra"><br><div class="gmail_quote">2017-06-23 1:13 GMT+08:00 Peter Lawrence via llvm-dev <span dir="ltr"><<a href="mailto:llvm-dev@lists.llvm.org" target="_blank">llvm-dev@lists.llvm.org</a>></span>:<br><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"><div style="word-wrap:break-word">Chenwj,<div>             In ISD the UNDEF node (i.e. SDValue) is an "undefined value”,</div><div>not “undefined behavior”, i.e. not scary!. You can think of it as an</div><div>uninitialized / don’t-care register, or in a vector an uninitialized / don’t-care element.</div></div></blockquote><div class="gmail_default" style="font-family:arial,helvetica,sans-serif"><br></div><div class="gmail_default" style="font-family:arial,helvetica,sans-serif">So the UNDEF node corresponds to undefined value in LLVM LangRef [1], right?</div><div class="gmail_default" style="font-family:arial,helvetica,sans-serif">And I can do whatever I want with those UNDEF nodes, right?</div><div class="gmail_default" style="font-family:arial,helvetica,sans-serif"><br></div><div class="gmail_default" style="font-family:arial,helvetica,sans-serif">Thanks.</div><div class="gmail_default" style="font-family:arial,helvetica,sans-serif"><br></div><div class="gmail_default" style="font-family:arial,helvetica,sans-serif">[1] <a href="http://llvm.org/docs/LangRef.html#undefined-values">http://llvm.org/docs/LangRef.html#undefined-values</a></div><div class="gmail_default" style="font-family:arial,helvetica,sans-serif"><br></div><div class="gmail_default" style="font-family:arial,helvetica,sans-serif">Regards,</div><div class="gmail_default" style="font-family:arial,helvetica,sans-serif">chenwj</div><div class="gmail_default" style="font-family:arial,helvetica,sans-serif">​</div></div>-- <br><div class="gmail_signature"><div dir="ltr"><div>Wei-Ren Chen (陳韋任)<br>Homepage: <a href="https://people.cs.nctu.edu.tw/~chenwj" target="_blank">https://people.cs.nctu.edu.tw/~chenwj</a></div></div></div>
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