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It is permissible to define macros prior to including a PCH, as long as
these definitions are disjoint from or identical to the macros in the
PCH. The PCH loading process replaces all libcpp data structures with those
from the PCH, so it is necessary to remember the extra macros separately and
then restore them after loading the PCH, which all is handled by
cpp_save_state() and cpp_read_state() in libcpp/pch.cc. The restoration
process consists of pushing a buffer containing the macro definition and
then lexing it from there, similar to how a command-line -D option is
processed. The current implementation does not attempt to set up the
line_map for this process, and so the locations assigned to the macros are
often not meaningful. (Similar to what happened in the past with lexing the
tokens out of a _Pragma string, lexing out of a buffer rather than a file
produces "sorta" reasonable locations that are often close enough, but not
reliably correct.)
Fix that up by remembering enough additional information (more or less, an
expanded_location for each macro definition) to produce a reasonable
location for the newly restored macros.
One issue that came up is the treatment of command-line-defined macros. From
the perspective of the generic line_map data structures, the command-line
location is not distinguishable from other locations; it's just an ordinary
location created by the front ends with a fake file name by convention. (At
the moment, it is always the string `<command-line>', subject to
translation.) Since libcpp needs to assign macros to that location, it
needs to know what location to use, so I added a new member
line_maps::cmdline_location for the front ends to set, similar to how
line_maps::builtin_location is handled.
This revealed a small issue, in c-opts.cc we have:
/* All command line defines must have the same location. */
cpp_force_token_locations (parse_in, line_table->highest_line);
But contrary to the comment, all command line defines don't actually end up
with the same location anymore. This is because libcpp/lex.cc has been
expanded (r6-4873) to include range information on the returned
locations. That logic has never been respecting the request of
cpp_force_token_locations. I believe this was not intentional, and so I have
corrected that here. Prior to this patch, the range logic has been leading
to command-line macros all having similar locations in the same line map (or
ad-hoc locations based from there for sufficiently long tokens); with this
change, they all have exactly the same location and that location is
recorded in line_maps::cmdline_location.
With that change, then it works fine for pch.cc to restore macros whether
they came from the command-line or from the main file.
gcc/c-family/ChangeLog:
PR preprocessor/105608
* c-opts.cc (c_finish_options): Set new member
line_table->cmdline_location.
* c-pch.cc (c_common_read_pch): Adapt linemap usage to changes in
libcpp pch.cc; it is now possible that the linemap is in a different
file after returning from cpp_read_state().
libcpp/ChangeLog:
PR preprocessor/105608
* include/line-map.h: Add new member CMDLINE_LOCATION.
* lex.cc (get_location_for_byte_range_in_cur_line): Do not expand
the token location to include range information if token location
override was requested.
(warn_about_normalization): Likewise.
(_cpp_lex_direct): Likewise.
* pch.cc (struct saved_macro): New local struct.
(struct save_macro_data): Change DEFNS vector to hold saved_macro
rather than uchar*.
(save_macros): Adapt to remember the location information for each
saved macro in addition to the definition.
(cpp_prepare_state): Likewise.
(cpp_read_state): Use the saved location information to generate
proper locations for the restored macros.
gcc/testsuite/ChangeLog:
PR preprocessor/105608
* g++.dg/pch/line-map-3.C: Remove xfails.
* g++.dg/pch/line-map-4.C: New test.
* g++.dg/pch/line-map-4.Hs: New test.
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