<html>
<head>
<meta content="text/html; charset=utf-8" http-equiv="Content-Type">
</head>
<body bgcolor="#FFFFFF" text="#000000">
<p>Hi all,</p>
<p>thanks!</p>
<p>> Not sure if it's described anywhere off the top of my head;
if there isn't a comment describing this on the declaration of
LowerOperation or LowerOperationWrapper, it would probably be good
to add one. Returning SDValue() should be "fine" in all cases (it
might lead to a fatal error if we can't actually lower the
operation). <br>
</p>
<p>Does this sound good?</p>
<p><tt>diff --git a/include/llvm/Target/TargetLowering.h
b/include/llvm/Target/TargetLowering.h</tt><tt><br>
</tt><tt>index 01c5c51..41edcc6 100644</tt><tt><br>
</tt><tt>--- a/include/llvm/Target/TargetLowering.h</tt><tt><br>
</tt><tt>+++ b/include/llvm/Target/TargetLowering.h</tt><tt><br>
</tt><tt>@@ -2830,7 +2830,8 @@ public:</tt><tt><br>
</tt><tt> /// target, which are registered to use 'custom'
lowering, and whose defined</tt><tt><br>
</tt><tt> /// values are all legal. If the target has no
operations that require custom</tt><tt><br>
</tt><tt> /// lowering, it need not implement this. The default
implementation of this</tt><tt><br>
</tt><tt>- /// aborts.</tt><tt><br>
</tt><tt>+ /// aborts. Returning SDValue() is ok and signals that
the input node</tt><tt><br>
</tt><tt>+ /// should be further handled by the caller instead.</tt><tt><br>
</tt><tt> virtual SDValue LowerOperation(SDValue Op,
SelectionDAG &DAG) const;</tt><tt><br>
</tt><tt> </tt><tt><br>
</tt><tt> /// This callback is invoked when a node result type
is illegal for the</tt><br>
</p>
<p>/ Jonas</p>
<p><br>
</p>
<div class="moz-cite-prefix">On 2017-01-23 22:59, Hal Finkel via
llvm-dev wrote:<br>
</div>
<blockquote cite="mid:2f40c5d7-d682-b174-e50a-de4e99152a4a@anl.gov"
type="cite">
<meta content="text/html; charset=utf-8" http-equiv="Content-Type">
<p><br>
</p>
<div class="moz-cite-prefix">On 01/23/2017 02:41 PM, Matt
Arsenault via llvm-dev wrote:<br>
</div>
<blockquote
cite="mid:755F29A7-F561-4FCD-A424-829A7B03141A@gmail.com"
type="cite">
<meta http-equiv="Content-Type" content="text/html;
charset=utf-8">
<br class="">
<div>
<blockquote type="cite" class="">
<div class="">On Jan 23, 2017, at 12:36, Friedman, Eli via
llvm-dev <<a moz-do-not-send="true"
href="mailto:llvm-dev@lists.llvm.org" class="">llvm-dev@lists.llvm.org</a>>
wrote:</div>
<br class="Apple-interchange-newline">
<div class=""><span style="font-family: Helvetica;
font-size: 12px; font-style: normal; font-variant-caps:
normal; font-weight: normal; letter-spacing: normal;
orphans: auto; text-align: start; text-indent: 0px;
text-transform: none; white-space: normal; widows: auto;
word-spacing: 0px; -webkit-text-stroke-width: 0px;
float: none; display: inline !important;" class="">On
1/23/2017 5:21 AM, Jonas Paulsson wrote:</span><br
style="font-family: Helvetica; font-size: 12px;
font-style: normal; font-variant-caps: normal;
font-weight: normal; letter-spacing: normal; orphans:
auto; text-align: start; text-indent: 0px;
text-transform: none; white-space: normal; widows: auto;
word-spacing: 0px; -webkit-text-stroke-width: 0px;"
class="">
<blockquote type="cite" style="font-family: Helvetica;
font-size: 12px; font-style: normal; font-variant-caps:
normal; font-weight: normal; letter-spacing: normal;
orphans: auto; text-align: start; text-indent: 0px;
text-transform: none; white-space: normal; widows: auto;
word-spacing: 0px; -webkit-text-size-adjust: auto;
-webkit-text-stroke-width: 0px;" class="">Hi Eli,<br
class="">
<br class="">
I would like to clarify generally what the difference is
between returning SDValue() and Op (input argument
unchanged) from LowerOperation()?<br class="">
<br class="">
My understanding is that returning SDValue() means that
Target gives up, and the common code is supposed to
handle it. Returning Op, the unchanged argument, means
that the Target is happy with the node as it is, and the
common code can move on to something else.<br class="">
</blockquote>
<br style="font-family: Helvetica; font-size: 12px;
font-style: normal; font-variant-caps: normal;
font-weight: normal; letter-spacing: normal; orphans:
auto; text-align: start; text-indent: 0px;
text-transform: none; white-space: normal; widows: auto;
word-spacing: 0px; -webkit-text-stroke-width: 0px;"
class="">
<span style="font-family: Helvetica; font-size: 12px;
font-style: normal; font-variant-caps: normal;
font-weight: normal; letter-spacing: normal; orphans:
auto; text-align: start; text-indent: 0px;
text-transform: none; white-space: normal; widows: auto;
word-spacing: 0px; -webkit-text-stroke-width: 0px;
float: none; display: inline !important;" class="">This
is right.</span></div>
</blockquote>
</div>
</blockquote>
</blockquote>
<blockquote cite="mid:2f40c5d7-d682-b174-e50a-de4e99152a4a@anl.gov"
type="cite">
<blockquote
cite="mid:755F29A7-F561-4FCD-A424-829A7B03141A@gmail.com"
type="cite">
<div>
<blockquote type="cite" class=""> </blockquote>
</div>
<br class="">
<div class="">This sounds backwards. Returning SDValue() means
the node should be treated as legal. Returning the original
operation should hit the expand path.</div>
</blockquote>
<br>
No, I think that was correct. The code in
lib/CodeGen/SelectionDAG/LegalizeDAG.cpp reads:<br>
<br>
switch (Action) {<br>
case TargetLowering::Legal:<br>
return;<br>
case TargetLowering::Custom: {<br>
// FIXME: The handling for custom lowering with multiple
results is<br>
// a complete mess.<br>
if (SDValue Res = TLI.LowerOperation(SDValue(Node, 0), DAG))
{<br>
if (!(Res.getNode() != Node || Res.getResNo() != 0))<br>
return;<br>
<br>
...<br>
<br>
ReplaceNode(Node, ResultVals.data());<br>
return;<br>
}<br>
LLVM_FALLTHROUGH;<br>
}<br>
case TargetLowering::Expand:<br>
if (ExpandNode(Node))<br>
return;<br>
<br>
So, if you return an SDValue() then it will Expand. If you return
the original node, that is equivalent to Legal. Otherwise, you're
requesting a replacement. The logic for loads/stores and vectors
is handled separately (but is similar).<br>
<br>
-Hal<br>
<br>
<blockquote
cite="mid:755F29A7-F561-4FCD-A424-829A7B03141A@gmail.com"
type="cite">
<div class=""><br class="">
</div>
<div class="">-Matt</div>
<br>
<fieldset class="mimeAttachmentHeader"></fieldset>
<br>
<pre wrap="">_______________________________________________
LLVM Developers mailing list
<a moz-do-not-send="true" class="moz-txt-link-abbreviated" href="mailto:llvm-dev@lists.llvm.org">llvm-dev@lists.llvm.org</a>
<a moz-do-not-send="true" class="moz-txt-link-freetext" href="http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev">http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev</a>
</pre>
</blockquote>
<br>
<pre class="moz-signature" cols="72">--
Hal Finkel
Lead, Compiler Technology and Programming Languages
Leadership Computing Facility
Argonne National Laboratory</pre>
<br>
<fieldset class="mimeAttachmentHeader"></fieldset>
<br>
<pre wrap="">_______________________________________________
LLVM Developers mailing list
<a class="moz-txt-link-abbreviated" href="mailto:llvm-dev@lists.llvm.org">llvm-dev@lists.llvm.org</a>
<a class="moz-txt-link-freetext" href="http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev">http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev</a>
</pre>
</blockquote>
<br>
</body>
</html>