Description:
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Calling DOMNode::C14N() is way slower on DOMDocument objects that are created on the fly compared to DOMDocuments loaded from a string file.

Calling DOMDocument::normalizeDocument() doesn't make a difference despite the documentation stating: "This method acts as if you saved and then loaded the document, putting the document in a "normal" form."


But in the end it's still way faster to get the XML string and load it in a new DOMDocument - which is counter intuitive.

Code to demonstrate this can be found here:
https://gist.github.com/Luxian/1c732d13c12ca03835828a1553c39e4f 
https://3v4l.org/1fFB3 (limited to 200 items to not abuse the platform)

If you run the example code with 500 items you should get something like this:

Testing with 500 items
Generated DOM… 2.56458 seconds
Generated DOM with normalizeDocument()… 2.60349 seconds
Export and re-import DOM… 0.06695 seconds


Test script:
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https://gist.github.com/Luxian/1c732d13c12ca03835828a1553c39e4f 

Expected result:
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$oldDom->normalizeDocument() 
// should be the same as
$newDom->loadXML($oldDom->saveXML());

Actual result:
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40x worse performance when calling C14N()