Re: [5/18] argv_ref speedup: add notion of quote age

Hi Eric,

On 7 Dec 2007, at 22:14, Eric Blake wrote:
> The next in the series.  I hope I got everything correct on the head  
> - the
> addition of changesyntax made porting this patch more interesting,  
> because
> there were more corner cases to think about.  In general, this patch  
> adds
> some timing overhead, and has little impact on memory (on head, it
> actually uses slightly less memory).
>
> The idea behind this patch is as follows.  Since m4 allows  
> redefining the
> behavior of the input engine on the fly (changequote, changecom,
> changeword, changesyntax), we must ensure correct reparse in those  
> corner
> cases.  Our goal is to reparse text as few times as possible - once  
> text
> has been parsed, we know what quoting rules it follows, so we cache  
> that
> information alongside each string of parsed text.  Then when  
> reparsing, we
> can see if the quote age remains the same, in which case we don't  
> have to
> waste time parsing that string, but can use the entire string as is.
> Setting quote_age to be hardcoded to 0 will produce the same  
> results, but
> without the benefit of reparsing.
>
> 2007-12-07  Eric Blake  <[email protected]>
>
> 	Stage 5: add notion of quote age.
> 	* src/input.c: Comment cleanups.
> 	(current_quote_age): New global variable.
> 	(set_quote_age): New helper function.
> 	(input_init, set_word_regexp): Use it.
> 	(set_quotes, set_comment): Likewise, and detect no-op changes.
> 	(quote_age, safe_quotes): New functions.
> 	(next_token): Track quote age.
> 	* src/m4.h (struct token_data): Add quote_age member.
> 	(TOKEN_DATA_QUOTE_AGE, quote_age, safe_quotes): New prototypes.
> 	* src/macro.c (struct macro_arguments): Add quote_age member.
> 	(expand_token): Alter signature and track quote age.
> 	(expand_input, expand_argument): All callers changed.
> 	(collect_arguments, make_argv_ref): Track quote age.
> 	(arg_text, arg_len, arg_func): Detect type mismatch.
> 	* doc/m4.texinfo (Ifelse, Changequote): Add more tests.
> 	(Incompatibilities): Fix typo.
> 	* examples/wraplifo.m4: New file.
> 	* examples/Makefile.am (EXTRA_DIST): Distribute it.


IMHO, the nice explanations you are giving above the ChangeLog entries  
in
this patch series really belong inside the ChangeLog itself.  I would  
have
found understanding the semantics of the patches much harder without  
that
extra text, and I suspect future readers of the ChangeLog and the  
changeset
history would benefit equally.

Cheers,
	Gary
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