[Bug c++/113976] [11/12/13/14 Regression] explicit instantiation of const variable template following implicit instantiation is assembled in .rodata instead of .bss

["tamiko at gentoo dot org" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113976

--- Comment #2 from Matthias Maier <tamiko at gentoo dot org> ---
I have bisected the issue to:

commit 2ec399d8a6c9c26d69b73faf77c694fa3915dcec (HEAD, refs/bisect/bad)
Author: Joerg Sonnenberger <joerg@bec.de>
Date:   Fri Sep 1 10:26:00 2017 -0600

    varasm.c (bss_initializer_p): Do not put constants into .bss

            * varasm.c (bss_initializer_p): Do not put constants into .bss
            (categorize_decl_for_section): Handle bss_initializer_p returning
            false when DECL_INITIAL is NULL.

            * gcc.target/i386/const-in-bss.c: New test.

    From-SVN: r251602


(But I have the feeling that the issue really lies in `mpi_type_id_for_type<T>`
being misidentified as a constant (suitable for .rodata). The above commit
might have merely made the issue visible by turning it into a segfault.)



bisect log:
git bisect start
# good: [883312dc79806f513275b72502231c751c14ff72] Use ucontext_t not struct
ucontext in linux-unwind.h files.
git bisect good 883312dc79806f513275b72502231c751c14ff72
# bad: [406c2abec3f998e9064919b22db62f38a7c0e7b9] * gennews (files): Add files
for GCC 8.
git bisect bad 406c2abec3f998e9064919b22db62f38a7c0e7b9
# bad: [9cf7bfd919f394595c0ac561ed67b333a39ae51e] PR 83070 Fix -Wsign-compare
warning
git bisect bad 9cf7bfd919f394595c0ac561ed67b333a39ae51e
# bad: [01f44e44faf37fc34775b9e28e46d1c9243b247d] i386: Update preferred stack
boundary for leaf functions
git bisect bad 01f44e44faf37fc34775b9e28e46d1c9243b247d
# good: [30af3a2bbd315bf82363c066a335a040dede9901] Boolify some parameters.
git bisect good 30af3a2bbd315bf82363c066a335a040dede9901
# good: [3ca3c6ef7110fb842cf8175a58d91d239c418bbe] re PR sanitizer/81902 (new
-fsanitize=pointer-overflow option undocumented)
git bisect good 3ca3c6ef7110fb842cf8175a58d91d239c418bbe
# bad: [0f99f8e6d63038b68e5e7af950ff9e329bdc40ad] Daily bump.
git bisect bad 0f99f8e6d63038b68e5e7af950ff9e329bdc40ad
# bad: [95edbf5e5fb2c57ceda70cdf277d9b7655c1796e] Minor reformatting.
git bisect bad 95edbf5e5fb2c57ceda70cdf277d9b7655c1796e
# bad: [806fcf7183377c7df062a7fa0bcf9d0ce8ea1fc0] trans.c
(adjust_for_implicit_deref): New function.
git bisect bad 806fcf7183377c7df062a7fa0bcf9d0ce8ea1fc0
# bad: [ca1150f0129abd2b0b52ad0c701a6bd7e0a1fc76] re PR sanitizer/81981
(-fsanitize=undefined makes a -Wmaybe-uninitialized warning disappear)
git bisect bad ca1150f0129abd2b0b52ad0c701a6bd7e0a1fc76
# bad: [0c949f0a1ce9cfa8c48e62628493140d60e65ea7] re PR libquadmath/81848 (Add
PowerPC support to libquadmath)
git bisect bad 0c949f0a1ce9cfa8c48e62628493140d60e65ea7
# bad: [beb8b5c154e57f5c2e3e6f372c2bae9a10f619b4] class.c
(finish_struct_methods): Done clear DECL_IN_AGGR_P here.
git bisect bad beb8b5c154e57f5c2e3e6f372c2bae9a10f619b4
# good: [db6bb1ec036f180584d221cdc66dff7bb7180d7a] S/390: PR82012: Implement
CAN_INLINE_P target hook.
git bisect good db6bb1ec036f180584d221cdc66dff7bb7180d7a
# bad: [e035be33793fa4aef8cff3358c9670a648d5d273] Fix excess precision handling
of compound assignments (PR c/82071).
git bisect bad e035be33793fa4aef8cff3358c9670a648d5d273
# bad: [2ec399d8a6c9c26d69b73faf77c694fa3915dcec] varasm.c (bss_initializer_p):
Do not put constants into .bss
git bisect bad 2ec399d8a6c9c26d69b73faf77c694fa3915dcec
# first bad commit: [2ec399d8a6c9c26d69b73faf77c694fa3915dcec] varasm.c
(bss_initializer_p): Do not put constants into .bss