<div dir="ltr">Thanks Michael for these explanations,<br>It is very good to know these details. And a good motivation to buy Saxon-SA.<br><br>Rémi<br><br><div class="gmail_quote">On Fri, Oct 3, 2008 at 4:27 PM, Michael Kay <span dir="ltr"><<a href="mailto:mike@saxonica.com">mike@saxonica.com</a>></span> wrote:<br>
<blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;">
<div>
<div dir="ltr" align="left"><span><font size="2" color="#0000ff" face="Arial">This is a case where Saxon (even Saxon-SA) has stopped
optimizing when it could have achieved a little more. The relevant part of the
final expression tree is</font></span></div>
<div dir="ltr" align="left"><span><font size="2" color="#0000ff" face="Arial"></font></span> </div>
<div dir="ltr" align="left"><span><font size="2" color="#0000ff" face="Arial">
<return><br>
<sequence><br>
<choose><br>
<when><br>
<compareToInteger op="ge"
value="4"><div class="Ih2E3d"><br>
<literal value="3"
type="xs:integer"/><br></div>
</compareToInteger><br>
</when><br>
<then><br>
<directElement name="debug"
validation="preserve"><br>
<variableReference
name="dosmthg"/><br>
</directElement><br>
</then><br>
</choose><div class="Ih2E3d"><br>
<variableReference
name="dosmthg"/><br>
</sequence><br>
</return></div></font></span></div>
<div dir="ltr" align="left"><span><font size="2" color="#0000ff" face="Arial"></font></span> </div>
<div dir="ltr" align="left"><span><font size="2" color="#0000ff" face="Arial">and it hasn't noticed that the <when> condition is
now constant.</font></span></div>
<div dir="ltr" align="left"><span><font size="2" color="#0000ff" face="Arial"></font></span> </div>
<div dir="ltr" align="left"><span><font size="2" color="#0000ff" face="Arial">Deciding when to stop optimizing is the trickiest part of
the exercise - if you go on too long, optimization can take longer than any
run-time savings it is delivering. In this occasion, two more passes would
have paid dividends - one to evaluate the <when> condition, the other to
reduce the <choose> to ().</font></span></div><div class="Ih2E3d">
<div dir="ltr" align="left"><span><font size="2" color="#0000ff" face="Arial"></font></span> </div>
<div dir="ltr" align="left"><span><font size="2" color="#0000ff" face="Arial">Michael Kay</font></span></div>
<div dir="ltr" align="left"><span><font size="2" color="#0000ff" face="Arial"><a href="http://www.saxonica.com/" target="_blank">http://www.saxonica.com/</a></font></span></div>
<div dir="ltr" align="left"><span><font size="2" color="#0000ff" face="Arial"></font></span> </div>
<div dir="ltr" align="left"><span><font size="2" color="#0000ff" face="Arial"> </font></span></div><br>
</div><blockquote dir="ltr" style="border-left: 2px solid rgb(0, 0, 255); padding-left: 5px; margin-left: 5px; margin-right: 0px;">
<div dir="ltr" align="left" lang="en-us">
<hr>
<font size="2" face="Tahoma"><div class="Ih2E3d"><b>From:</b> <a href="mailto:talk-bounces@x-query.com" target="_blank">talk-bounces@x-query.com</a>
[mailto:<a href="mailto:talk-bounces@x-query.com" target="_blank">talk-bounces@x-query.com</a>] <b>On Behalf Of </b>Rémi
Dewitte<br></div><b>Sent:</b> 03 October 2008 14:24<div class="Ih2E3d"><br><b>To:</b>
<a href="mailto:talk@x-query.com" target="_blank">talk@x-query.com</a><br></div><b>Subject:</b> [xquery-talk] Re:
Optimizations<br></font><br></div><div><div></div><div class="Wj3C7c">
<div></div>
<div dir="ltr">Hi again,<br><br>In the same spirit, this is not at all
optimized.<br>Maybe I need Saxon SA ?<br><br><br>declare variable $level as
xs:integer := 3 ;<br><br>declare function local:debug($l as
xs:integer,$what){<br> if($l >=4) then<br>
<debug>{$what}</debug><br> else ()<br>};<br><br>let $dosmthg
:= <oki>test
trace</oki><br><br>return<br>(local:debug($level,$dosmthg),$dosmthg)<br><br><br>Rémi<br><br>
<div class="gmail_quote">On Fri, Oct 3, 2008 at 3:17 PM, Rémi Dewitte <span dir="ltr"><<a href="mailto:remi@gide.net" target="_blank">remi@gide.net</a>></span>
wrote:<br>
<blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;">
<div dir="ltr">Hi,<br><br>I have made a little experiment after reading
Michael (Kay) blog posts about optimizations and recent James Fuller
article.<br><br>I have a question quite specific to saxon still interesting
in general.<br><br>Why in the following example even the function call is
not skipped ?<br><br><br>XQuery is ::<br><br>declare variable $level :=
3;<br><br>declare function local:debug($what){<br> if($level >=4)
then<br> <debug>{$what}</debug><br> else
()<br>};<br><br>let $dosmthg := <oki>test
trace</oki><br><br>return<br>(local:debug($dosmthg),$dosmthg)<br><br>When
I run saxon with -explain we get <br><br><query><br>
<globalVariables><br> <declareVariable
name="level"><br> <literal value="3"
type="xs:integer"/><br>
</declareVariable><br> </globalVariables><br>
<declareFunction name="local:debug"
tailRecursive="false"><br> <literal
value="()"/><br> </declareFunction><br>
<body><br> <let variable="dosmthg"
as="element(oki, {<a href="http://www.w3.org/2001/XMLSchema%7Duntyped" target="_blank">http://www.w3.org/2001/XMLSchema}untyped</a>)"><br>
<be><br> <directElement
name="oki"
validation="skip"><br>
<valueOf><br>
<literal value="test trace"
type="xs:string"/><br>
</valueOf><br>
</directElement><br>
</be><br>
<return><br>
<sequence><br>
<functionCall name="local:debug"
tailCall="false"><br>
<variableReference
name="dosmthg"/><br>
</functionCall><br>
<variableReference
name="dosmthg"/><br>
</sequence><br>
</return><br> </let><br>
</body><br></query><br><br>Cheers,<br>Rémi<br></div></blockquote></div><br></div></div></div></blockquote></div>
</blockquote></div><br></div>