[fpc-devel] Question about typeconv nodes

[J. Gareth Moreton]

Hi everyone,

I've noticed that, in many units, the generated node trees produce a lot 
of typeconv nodes with convtype=tc_equal.  For example (4th line - this 
is generated with DEBUG_NODE_XML):

<statementn pos="53,30">
...<assignn resultdef="$void" pos="53,9">
......<subscriptn resultdef="Double" pos="53,10" flags="nf_write">
.........<typeconvn resultdef="complex" pos="53,9" flags="nf_absolute" 
convtype="tc_equal">
............<loadn resultdef="complex" pos="53,10" flags="nf_write">
...............<symbol>result</symbol>
............</loadn>
.........</typeconvn>
.........<field>RE</field>
......</subscriptn>
......<addn resultdef="Double" pos="53,23">
.........<subscriptn resultdef="Double" pos="53,19">
............<loadn resultdef="complex" pos="53,17">
...............<symbol>Z1</symbol>
............</loadn>
............<field>RE</field>
.........</subscriptn>
.........<subscriptn resultdef="Double" pos="53,27">
............<loadn resultdef="complex" pos="53,25">
...............<symbol>Z2</symbol>
............</loadn>
............<field>RE</field>
.........</subscriptn>
......</addn>
...</assignn>
</statementn>

As an experiment, I tried to simplify the node tree on x86_64 by 
stripping out typeconv nodes where the convtype=tc_equal, 
resultdef=left.resultdef (so it truly is an equal conversion) and the 
type is unmanaged (including managed types can sometimes change the 
assembly language quite significantly, like how often reference 
incrementors or decrementors are called - I figured that playing around 
with those is risky).  Long story short, it tends to help with producing 
more efficient machine code.

Is there something I've missed where such typeconv nodes are necessary?  
I figure it's something to do with the "nf_absolute" flag, but I haven't 
quite grasped it yet.  Any help would be appreciated.

Gareth aka. Kit

P.S. My desire for removing unnecessary typeconv nodes is to help with 
vectorisation.


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