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[XQuery Talk Mailing List Archive Home] [By Date] [By Thread] [By Subject] [By Author] [Recent Entries] [Reply To This Message] Re: OptimizationsMichael Kay mike at saxonica.comFri Oct 3 16:27:01 PDT 2008
 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
<return>
<sequence>
<choose>
<when>
<compareToInteger op="ge" value="4">
<literal value="3" type="xs:integer"/>
</compareToInteger>
</when>
<then>
<directElement name="debug" validation="preserve">
<variableReference name="dosmthg"/>
</directElement>
</then>
</choose>
<variableReference name="dosmthg"/>
</sequence>
</return>
and it hasn't noticed that the <when> condition is now constant.
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 ().
Michael Kay
http://www.saxonica.com/
_____
From: http://x-query.com/mailman/listinfo/talk [mailto:http://x-query.com/mailman/listinfo/talk] On Behalf
Of Rémi Dewitte
Sent: 03 October 2008 14:24
To: http://x-query.com/mailman/listinfo/talk
Subject: Re: Optimizations
Hi again,
In the same spirit, this is not at all optimized.
Maybe I need Saxon SA ?
declare variable $level as xs:integer := 3 ;
declare function local:debug($l as xs:integer,$what){
if($l >=4) then
<debug>{$what}</debug>
else ()
};
let $dosmthg := <oki>test trace</oki>
return
(local:debug($level,$dosmthg),$dosmthg)
Rémi
On Fri, Oct 3, 2008 at 3:17 PM, Rémi Dewitte <http://x-query.com/mailman/listinfo/talk> wrote:
Hi,
I have made a little experiment after reading Michael (Kay) blog posts about
optimizations and recent James Fuller article.
I have a question quite specific to saxon still interesting in general.
Why in the following example even the function call is not skipped ?
XQuery is ::
declare variable $level := 3;
declare function local:debug($what){
if($level >=4) then
<debug>{$what}</debug>
else ()
};
let $dosmthg := <oki>test trace</oki>
return
(local:debug($dosmthg),$dosmthg)
When I run saxon with -explain we get
<query>
<globalVariables>
<declareVariable name="level">
<literal value="3" type="xs:integer"/>
</declareVariable>
</globalVariables>
<declareFunction name="local:debug" tailRecursive="false">
<literal value="()"/>
</declareFunction>
<body>
<let variable="dosmthg" as="element(oki,
{http://www.w3.org/2001/XMLSchema}untyped
<http://www.w3.org/2001/XMLSchema%7Duntyped> )">
<be>
<directElement name="oki" validation="skip">
<valueOf>
<literal value="test trace" type="xs:string"/>
</valueOf>
</directElement>
</be>
<return>
<sequence>
<functionCall name="local:debug" tailCall="false">
<variableReference name="dosmthg"/>
</functionCall>
<variableReference name="dosmthg"/>
</sequence>
</return>
</let>
</body>
</query>
Cheers,
Rémi
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