[fpc-devel] Progress on pure functions

[J. Gareth Moreton]

On 14/12/2022 10:18, Sven Barth via fpc-devel wrote:
>
>     Wouldn't it make more sense to ensure that the Str() and Val()
>     intrinsic work correctly inside "pure" functions? After all the
>     compiler can then simply evaluate the inlinen nodes and does not
>     have to "interpret" a ton of other code as well.
>
So I just tried a simple test with "System.Str(5, Output);" (with Output 
defined as a string), and it produced the following nodes:

<calln resultdef="$void" pos="12,3">
...<procname>$fpc_shortstr_sint(Int64;Int64;out OpenString;<const 
Int64>);</procname>
...<callparan resultdef="Int64" pos="12,3">
......<ordconstn resultdef="Int64" pos="12,3" flags="nf_explicit" 
rangecheck="TRUE">
.........<value>255</value>
......</ordconstn>
...</callparan>
...<callparan resultdef="OpenString" pos="12,23">
......<loadn resultdef="ShortString" pos="12,23" flags="nf_write">
.........<symbol>OUTPUT</symbol>
......</loadn>
...</callparan>
...<callparan resultdef="Int64" pos="12,3">
......<ordconstn resultdef="Int64" pos="12,3" rangecheck="FALSE">
.........<value>-1</value>
......</ordconstn>
...</callparan>
...<callparan resultdef="Int64" pos="12,15">
......<ordconstn resultdef="Int64" pos="12,15" rangecheck="FALSE">
.........<value>5</value>
......</ordconstn>
...</callparan>
</calln>

This is before the first pass, so the parser immediately replaces it 
with a call to the internal compiler procedure.

How should I handle this? There are a few problems I need to consider.  
If I use a new kind of inline node that expands into a regular call 
after the first pass, I'll still need to handle the case where it is a 
call node because there are situations during purity analysis where 
nested pure functions are not analysed because their actual parameters 
haven't yet been fully calculated (usually requires another found of 
constant propagation and inline simplification).  It may be that I need 
to add some kind of field to the TCallNode to indicate which internal 
function it's referring to.

I'll try to do a new merge request soon so Str and Val can be simplified 
at the node level, as this can easily have benefits outside of pure 
functions.

Kit
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