Re: Ada, treelang needs to be converted to --enable-mapped-location

[Per Bothner <per@bothner.com>]

Richard Kenner wrote:

>     To summarize:  you can create the Source_Ptr -> source_location
>     mapping in two basic ways:  interleaved with lexing, or as a
>     mapping when the Source_Buffer is read in.  Whichever you prefer.
> 
> I guess the question is what does "read" mean in the context of a
> compiler that doesn't call the lexer library.

I'm confused.  What is "the lexer library"?  It certainly seems that
Ada calls a lexer library - it appears to be the Scans package. If you 
mean libcpp (except for line-map.[hc]), that's not a lexer library,
that's a pre-processor library.  It is not used for Java or Fortran
either.

Don't get confused by line-map.[hc] being in libcpp.  That's mainly
because some people wanted to put libcpp in a separate top-level
library, and because libcpp depends on line-map[hc].  Logically,
line-map.[hc] is a separate library, but that seemed overkill.

My intention by the word "read" was when when the character of the
source file are read into the compiler's Source_Buffer, which from
what I gather happens *before* lexing.

My suggestion that one option is to create thr Source_Ptr ->
source_location mapping (i.e. data structures to make the mapping
reasonably efficient) be done more-or-less at the same time as the
source file is read into a Source_Buffer and Source_Ptr mapping is
updated.

Alternatively, you can so it using call-backs to line-map.[hc] while the
Ada front-end is scanning the Source_buffer.  That is my recommendation.

> It's tricky to make calls from the Ada part of the code since, as Geert
> pointed out, that code is also used wiht non-GCC back-ends.

Yes, but that doesn't preclude using the line_map structure, even
with non-GCC back-ends.  There is no reason why the Ada front-end
can't use line_map for a program that say just does analysis and
never touches a tree or an rtx.

The Source_Ptr type appears to be an abstract source position encoded
as a int.  I see no reason why you can't change its *implementation*
to be the source_location type defined in line-map.h.  You can do this
*regardless* of whether "back-end" you use.  True, it's a non-trivial
change, and since I obviously don't know all the ramifications and
features of your current implementation, it's not my place to suggest
you make such a pervasive change.  However, my instinct is that would
be the best long-term solution.

> Moreover, it's quite common for the Ada front-end to read a file and
> no item in the file is in the produced tree.

Like C, C++, and Java.

>> So I'd interpret "read" as meaning "being asked to convert the first
> GNAT tree node using this file into a GCC node".

You can certainly do that.  It's not what I would have suggested, but
it may be a reasonable solution.

> Is there a way to find
> out if a filename has been seen already or do we need a separate hash table
> just for that purpose?

Whether a filename has been seen is a front-end issue.

You clearly don't need a separate hash table, if you're willing to add a
boolean field to the Source_Buffer type.

Alternatively, the (relatively new) TRANSLATION_UNIT_DECL may be a
reasonably place to hang per-source-file data.
-- 
	--Per Bothner
per@bothner.com   http://per.bothner.com/