<html><head><meta http-equiv="Content-Type" content="text/html charset=windows-1252"></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;"><br><div><div>On Dec 19, 2012, at 4:22 PM, Weiming Zhao <<a href="mailto:weimingz@codeaurora.org">weimingz@codeaurora.org</a>> wrote:</div><br class="Apple-interchange-newline"><blockquote type="cite"><meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1"><meta name="Generator" content="Microsoft Word 14 (filtered medium)"><base href="x-msg://102/"><style><!--
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</o:shapelayout></xml><![endif]--><div lang="EN-US" link="blue" vlink="purple"><div class="WordSection1"><p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">The change to InstrEmitter is to let it support ExtractSubReg / RegSequence to be connected to RegisterNode and CopyFrom node to be connected to a SubReg SDNode.<o:p></o:p></span></p><p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"> </span></p><p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">Normally, ExtractSubReg/RegSequence are only connected to a SDValue, but for inlineasem, we have to connect them to a VR.<o:p></o:p></span></p><p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">Existing inlineasm just emits multiple 32bit-typed VRs, it doesn’t need ExtractSubReg/RegSequence, so such scenarios are not encountered. <o:p></o:p></span></p><p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"> </span></p><p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">Now, this issue is exposed . <o:p></o:p></span></p><p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">So my patch let it handle more cases. It should be safe.</span></p></div></div></blockquote><div><br></div><div>It is important that you understand how data dependencies are modeled in SelectionDAG. They must be represented by DAG edges, and RegisterSDNode doesn't provide a DAG edge.</div><div><br></div><div>Calls and inline-asm nodes get their arguments from virtual or physical registers via RegisterSDNode arguments, but that only works because those registers are read or written by CopyToReg and/or CopyFromReg nodes that are *glued* to the call/asm nodes. The DAG edges carrying the data dependencies are provided by the CopyToReg / CopyFromReg nodes.</div><div><br></div><div>You can't simply allow REG_SEQUENCE and EXTRACT_SUBREG to operate on RegisterSDNodes since there is no DAG edge providing the data dependency. It would be completely unsafe to allow such DAG constructs.</div><div><br></div><div>It is also entirely unnecessary. You can feed your REG_SEQUENCE DAG edge into the CopyToReg node that is glued to an inline-asm node, and you can EXTRACT_SUBREG from a similarly glued CopyFromReg.</div><div><br></div><div>/jakob</div><div><br></div></div></body></html>