[Patch, fortran] PR 40958 Compress module files with zlib

[Janne Blomqvist <blomqvist dot janne at gmail dot com>]

Hi,

the attached patch reduces the size of module files on disk by
compressing them with zlib and storing them in the gzip format (RFC
1952). I chose zlib because it's a) ubiquitous and b) there's already
a copy of zlib in the GCC source tree, so this doesn't introduce any
further build
dependencies. Since the mod files with the patch are in the gzip
format, one can use tools like zcat, zless, zgrep, zdiff etc. to
inspect the uncompressed contents easily.

As the gzip file format already contains a CRC32 checksum, the patch
gets rid of the current MD5 checksumming, and instead compares the
CRC32 to determine whether a mod file should be replaced or not. As
the gz* functions can also handle uncompressed files, and because I
replaced the line with the MD5 sum with an empty line, there was no
need to bump the module version number.

Based on some testing with CP2K_2009-05-01.f90 (a single file
containing all of CP2K), the compile time with -fsyntax-only increased
from about 46 to 48 seconds, and the total size of the module files
were reduced from 124 MB to 13 MB.

(IMHO the increase in compile time is modest enough that it's not
worth doing the caching of uncompressed module files that I was
previously thinking about, especially considering that large projects
are invariably(?!) split over several source files, thereby reducing
the effectiveness of such a caching scheme.)

Regtested on x86_64-unknown-linux-gnu, Ok for trunk?

2013-04-09  Janne Blomqvist  <jb@gcc.gnu.org>

    PR fortran/40958
    * scanner.h: New file.
    * Make-lang.in: Dependencies on scanner.h.
    * scanner.c (gfc_directorylist): Move to scanner.h.
    * module.c: Don't include md5.h, include scanner.h and zlib.h.
    (MOD_VERSION): Add comment about backwards compatibility.
    (module_fp): Change type to gzFile.
    (ctx): Remove.
    (gzopen_included_file_1): New function.
    (gzopen_included_file): New function.
    (gzopen_intrinsic_module): New function.
    (write_char): Use gzputc.
    (read_crc32_from_module_file): New function.
    (read_md5_from_module_file): Remove.
    (gfc_dump_module): Use gz* functions instead of stdio, check gzip
    crc32 instead of md5.
    (read_module_to_tmpbuf): Use gz* functions instead of stdio.
    (gfc_use_module): Use gz* functions.


testsuite:

2013-04-09  Janne Blomqvist  <jb@gcc.gnu.org>

    PR fortran/40958
    * lib/gcc-dg.exp (scan-module): Uncompress module file before
    scanning.
    * gfortran.dg/module_md5_1.f90: Remove.


--
Janne Blomqvist

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