[PATCH] caret diagnostics (was: broken FE diagnostics wrt complex expressions)

["Manuel López-Ibáñez" <lopezibanez at gmail dot com>]

2008/8/14 Tom Tromey <tromey@redhat.com>:
>
> ISTR Manuel having a patch for caret diagnostic output... ?
>

I was planning to submit it this week to consider it for GCC 4.4
(disabled by default). I am still testing it. Bootstrap and regression
testing with --enable-languages=all,ada,obj-c++ is very slow even on a
x86_64-unknown-gnu-linux-pc.  But here it is for your reviewing and
testing pleasure. ;-)

The approach followed is to never free the input buffers and keep
pointers to the start of each line tracked by each line-map.

Alternative approaches are:

b) Re-open the file and fseek but that is not trivial since we need to
do it fast but still do all character conversions that we did when
libcpp opened it the first time. This is approximately what clang does
as far as I know except that they keep a cache of buffers ever
reopened. I think that thanks to our line-maps implementation, we can
do the seeking quite more efficiently in terms of computation time.
Still I do not know how to *properly* and *efficiently* re-open a
file.

c) Memcpy the relevant lines to a buffer for each line_map. This does
not seem a good approach under any circumstance. It means more memory
needed while the input buffers are opened (because we will end up with
two copies of the buffer) and we cannot free up that memory later
because we do not track how many references there are to each
line_maps, so we never free them. Perhaps the GC can help here? This
is the approach followed by GFortran.

Comments are welcome. However, I don't have time to do
memory/computation time tests (setting up the environment itself seems
very time consuming), so those would be *greatly* appreciated!

You can see many examples of the caret output by configuring with
--enable-caret-diagnostics, then reverting the changes to
gcc/testsuite/lib/gcc.exp and running the testsuite. Check the output
in the gcc.log and g++.log files.

Cheers,

Manuel.

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