Gfortran internal tree structure

[Daniel Kraft <domob1812 at gmail dot com>]

Hi,

while working on finalization, I'm at some places building expressions 
and statements to insert in the gfortran-internal tree (not the generic 
GIMPLE tree but gfc_code/gfc_expr and friends).

Sometimes I had to give it quite a few tries to get it right, as there 
are some minor details that I found non-intuitive or not perfectly clear.

For instance, that an IF statement consists of two gfc_code-parts with 
EXEC_IF, one being the block-member of the other, and that the condition 
is in the expr-member of the *inner* member.  (At least that's what my 
tests suggested and what's working for me at the moment.)

It would surely be helpful to have some support here for anyone not 
familar with these details, but AFAIK there's no real documentation 
around (maybe a bit in the dump-tree.c file or what it's called, but 
that's not perfect).  What do you think about writing a (maybe just 
quite summarizing) documentation about how gfc_code statements and 
gfc_expr expressions have to be structured for IF, DO, things like "a+5" 
or "ALLOCATED(arr)" and whatever comes to mind?  Or is there already 
such documentation and I missed it?

If you want and I find time, I volunteer to start this in parallel to my 
coding; but I think for that I need at least a good reviewer as I'm not 
myself a guru on this topic :)  Additionally, if you think that's a good 
idea, I could write builder-functions (maybe in a new code file 
build-tree.c); for instance, given a code-block and a condition, build a 
complete (resolved?) IF-gfc_code block; and similar for other constructs 
and expressions (build a less-than expression given two operands or a 
function-call given the list of actual argument expressions and the 
symbl/symtree/name.  These could serve both as a secondary documentation 
on how such an expression really looks like and be used to combine this 
logic where it's used in the code (during parsing and at places like my 
finalization routines during resolution).

What do you think about this idea?  I can't promise I'll really find 
time to work on this soon, but at least for me these ideas sound 
reasonable and useful.

Daniel

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