[Bug debug/109805] LTO affecting -fdebug-prefix-map

["sergiodj at sergiodj dot net" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109805

--- Comment #9 from Sergio Durigan Junior <sergiodj at sergiodj dot net> ---
at(In reply to Richard Biener from comment #8)
> This works for me.  The consistency check is not fully implemented and
> instead
> of passing down no -fdebug-prefix-map the patch passes the first but warns:
>
> > ./xgcc -B. t.o t2.o -o t
> lto-wrapper: warning: option
> -fdebug-prefix-map=/home/rguenther/obj-trunk-g/gcc=/bbb with different
> values, using /home/rguenther/obj-trunk-g/gcc=/aaa
>
> to make consistency checking work we need to record -fcanon-prefix-map
> and the full set of -f{file,debug}-prefix-map options in order (I think
> file and debug variants can be considered the same) of the first TU and
> compare that to each of the following TUs.

Thanks a lot for the patch.  I tried it locally, and it indeed works for the
simple example I posted in the description of this bug.  However, for some
reason it doesn't seem to make a difference for the vim compilation.  I'm still
seeing a directory table like the following:

Directory table:
      [path(line_strp)]
 0     /home/ubuntu/vim/vim-9.0.1378/src/vim-basic (0)
 1     /usr/include/x86_64-linux-gnu/bits (57)
 2     /usr/include (92)

whereas if I pass -fdebug-prefix-map to LDFLAGS, the directory table becomes:

Directory table:
      [path(line_strp)]
 0     /usr/src/vim-2:9.0.1378-2ubuntu2~ppa1/src/vim-basic (0)
 1     /usr/include/x86_64-linux-gnu/bits (65)
 2     /usr/include (100)

which is what I expected to see.

> Note a link-time specified option will simply ignore all options from the
> compile-time (but only for the link-time unit, the compile-time debug info
> has already been generated with the originally specified options).

FWIW, I think this bug is related to #108534 (and the related discussion at
https://gcc.gnu.org/pipermail/gcc-patches/2022-November/606205.html).