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* document how tgotonode/tlabelnode copying works

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git-svn-id: trunk@42986 -
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Jonas Maebe 2019-09-13 19:06:34 +00:00
parent 31f0bfeb96
commit e3e23df7e2
1 changed files with 36 additions and 0 deletions
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36
compiler/nflw.pas
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@ -142,6 +142,42 @@ interface
private
labelnodeidx : longint;
public
{ * Set when creating the gotonode (since that's all we know at that
point).
* Used in pass_typecheck to find the corresponding labelnode (when a
labelnode is created for a tlabelsym, the label assigns itself to
the "code" field of the labelsym), which is then assigned to the
labelnode field
* After this, the labelsym is (and must) never be used anymore, and
instead the labelnode must always be used. The reason is that the
labelsym may not be owned by anything, and will be freed by the
label node when it gets freed
* The above is the reason why the labelsym field does not get copied
by tgotonode.dogetcopy, but instead the copy of the labelnode gets
tracked (both the labelnode and its goto nodes must always all be
copied).
The labelnode itself will not copy the labelsym either in dogetcopy.
Instead, since the link between the gotos and the labels gets
tracked via node tree references, the label node will generate a new
asmlabel on the fly and the goto node will get it from there (if the
goto node gets processed before the label node has been processed,
it will ask the label node to generate the asmsymbol at that point).
The original tlabelsym will get emitted only for the original
label node. It is only actually used if there is a reference to it
from
* an inline assembly block. Since inline assembly blocks cannot be
inlined at this point, it doesn't matter that this would break
in case the node gets copied
* global goto/label. Inlining is not supported for these, so no
problem here either for now.
* a load node (its symtableentry field). Since the symtableentry
of loadnodes is always expected to be valid, we cannot do like
with the goto nodes. Instead, we will create a new labelsym
when performing a dogetcopy of such a load node and assign this
labelsym to the copied labelnode (and vice versa)
}
labelsym : tlabelsym;
labelnode : tlabelnode;
exceptionblock : integer;