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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif"">Owen:<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif""><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif"">FoldingSet can implement similar concept, thanks.</span><span style="font-size:11.0pt;font-family:"Calibri","sans-serif""><o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif"">Patch updated
</span><span style="font-size:11.0pt;font-family:"Calibri","sans-serif""><a href="http://llvm-reviews.chandlerc.com/D1127"><span style="color:windowtext">http://llvm-reviews.chandlerc.com/D1127</span></a><o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif""><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif"">BTW, FoldingSet is a good data structure, but it copies many contents when implementing hash and cause a big performance penalty since it is wildly used in SelectionDAG;
meanwhile the hash value is calculated many times for same object. Our profiling data shows it consume about ~3-~5% of total time in llc; We may need to optimize it.</span><span style="font-size:11.0pt;font-family:"Calibri","sans-serif""><o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif""><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif"">Thanks<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif"">Wan Xiaofei<o:p></o:p></span></p>
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<p class="MsoNormal"><b><span style="font-size:10.0pt;font-family:"Tahoma","sans-serif"">From:</span></b><span style="font-size:10.0pt;font-family:"Tahoma","sans-serif""> Owen Anderson [mailto:resistor@mac.com]
<br>
<b>Sent:</b> Saturday, October 12, 2013 2:08 AM<br>
<b>To:</b> Wan, Xiaofei<br>
<b>Cc:</b> llvm-commits@cs.uiuc.edu LLVM<br>
<b>Subject:</b> Re: [PATCH] [Review Request] Improve getVTList() in SelectionDAG<o:p></o:p></span></p>
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<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">OK, I can see that it works. It seems like you’re basically implementing the same idiom as the existing FoldingSet class (<a href="http://llvm.org/docs/ProgrammersManual.html#llvm-adt-foldingset-h">http://llvm.org/docs/ProgrammersManual.html#llvm-adt-foldingset-h</a>).
Can you see if you could make use of that rather than rolling your own solution?<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">—Owen<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">On Oct 10, 2013, at 10:26 PM, Wan, Xiaofei <<a href="mailto:xiaofei.wan@intel.com">xiaofei.wan@intel.com</a>> wrote:<o:p></o:p></p>
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<br>
<o:p></o:p></p>
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<p class="MsoNormal"><span style="font-size:9.0pt">Owen:<br>
<br>
Thanks for your comments.<span class="apple-converted-space"> </span><br>
Patch updated<span class="apple-converted-space"> </span><a href="http://llvm-reviews.chandlerc.com/D1127">http://llvm-reviews.chandlerc.com/D1127</a><br>
<br>
SDVTList SelectionDAG::getVTList(EVT VT1, EVT VT2) {<br>
const EVT tmpVTs[2] = {VT1, VT2};<br>
return getVTList(tmpVTs, 2);<br>
}<br>
How does the lifetime of this array work out? It looks like SDVTListInfo captures the pointer to the EVT array, which was stack allocated. After this method returns, you're going to have a dangling pointer in the SDVTListInfo.<br>
[Xiaofei] Yes, tmpVTs is an array on the stack, but it is just used temporally to determine whether this SDVTList exist in the DenseMap, it won't be referenced anymore after that.<br>
<br>
SDVTList SelectionDAG::getVTList(const EVT *VTs, unsigned NumVTs) {<br>
SDVTListInfo Key(VTs, NumVTs);<br>
if (VTListMap.count(Key))<br>
return VTListMap[Key];<br>
<br>
EVT *Array = Allocator.Allocate<EVT>(NumVTs);<br>
std::copy(VTs, VTs + NumVTs, Array); -------------------------------------------------VTs is copied out to Array which will be stored in the DenseMap<br>
SDVTList Result = makeVTList(Array, NumVTs);<br>
Key.pVTs = Array; --------------------------------------------------VTs is not used any more.<br>
VTListMap.insert(std::make_pair(Key, Result));<br>
<br>
return Result;<br>
}<br>
<br>
Thanks<br>
Wan Xiaofei<br>
<br>
-----Original Message-----<br>
From: Owen Anderson [<a href="mailto:resistor@mac.com">mailto:resistor@mac.com</a>]<span class="apple-converted-space"> </span><br>
Sent: Friday, October 11, 2013 1:30 AM<br>
To: Wan, Xiaofei<br>
Cc:<span class="apple-converted-space"> </span><a href="mailto:llvm-commits@cs.uiuc.edu">llvm-commits@cs.uiuc.edu</a><span class="apple-converted-space"> </span>LLVM<br>
Subject: Re: [PATCH] [Review Request] Improve getVTList() in SelectionDAG<br>
<br>
Some feedback:<br>
<br>
<br>
<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:9.0pt">+ /// getEmptyKey() - A private constructor that returns an unknown<span class="apple-converted-space"> </span><br>
+ that is /// not equal to the tombstone key or SDVTListInfo().<br>
+ static SDVTListInfo getEmptyKey() {<br>
+ SDVTListInfo SDVTInfo;<br>
+ SDVTInfo.NumVTs = 0;<br>
+ return SDVTInfo;<br>
+ }<br>
+<br>
+ /// getTombstoneKey() - A private constructor that returns an<span class="apple-converted-space"> </span><br>
+ unknown that /// is not equal to the empty key or SDVTListInfo().<br>
+ static SDVTListInfo getTombstoneKey() {<br>
+ SDVTListInfo SDVTInfo;<br>
+ SDVTInfo.NumVTs = 0;<br>
+ return SDVTInfo;<br>
+ }<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:9.0pt"><br>
I don't think this is a valid implementation of the DenseMapInfo callbacks. getEmptyKey() and getTombstoneKey() have to return values that don't compare equal to each other.<br>
<br>
<br>
<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:9.0pt">+ const EVT pVTs[2] = {VT1, VT2};<br>
+ return getVTList(pVTs, 2);<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:9.0pt"><br>
How does the lifetime of this array work out? It looks like SDVTListInfo captures the pointer to the EVT array, which was stack allocated. After this method returns, you're going to have a dangling pointer in the SDVTListInfo.<br>
<br>
-Owen<br>
<br>
<D1127.5.patch><o:p></o:p></span></p>
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