[Bug c/83960] New: Bad assembler with debug and LTO

[simon at pushface dot org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=83960

            Bug ID: 83960
           Summary: Bad assembler with debug and LTO
           Product: gcc
           Version: 8.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
          Assignee: unassigned at gcc dot gnu.org
          Reporter: simon at pushface dot org
  Target Milestone: ---
              Host: x86_64-apple-darwin15
            Target: x64_64-apple-darwin15
             Build: x86_64-apple-darwin15

Fails at r256927 (and previously, I now find, at r255748) with -g -flto.

For empty.c,

int main(void)
{
  return 0;
}

this is OK:

$ gcc -flto empty.c

but this fails:

$ gcc -g -flto empty.c
/var/folders/_q/fvnxz46903z9hjh38fz0lyhm0000gs/T//ccYrmduC.s:93:8: error:
unsupported relocation with subtraction expression, symbol '_empty.c.8f1a73ad'
can not be undefined in a subtraction expression
        .quad   _empty.c.8f1a73ad-Lsection__debug_info+11
                ^
/var/folders/_q/fvnxz46903z9hjh38fz0lyhm0000gs/T//ccYrmduC.s:95:8: error:
unsupported relocation with subtraction expression, symbol '_empty.c.8f1a73ad'
can not be undefined in a subtraction expression
        .quad   _empty.c.8f1a73ad-Lsection__debug_info+182
                ^
lto-wrapper: fatal error: /opt/gcc-8.0.0/bin/gcc returned 1 exit status
compilation terminated.
collect2: fatal error: lto-wrapper returned 1 exit status
compilation terminated.

Compiler built with

$ gcc -v
Using built-in specs.
COLLECT_GCC=gcc
COLLECT_LTO_WRAPPER=/Volumes/Miscellaneous/tmp/opt/gcc-8.0.0/libexec/gcc/x86_64-apple-darwin15/8.0.1/lto-wrapper
Target: x86_64-apple-darwin15
Configured with: ../gcc/configure
--prefix=/Volumes/Miscellaneous/tmp/opt/gcc-8.0.0 --without-libiconv-prefix
--disable-libmudflap --disable-libstdcxx-pch --disable-libsanitizer
--disable-libcc1 --disable-libcilkrts --disable-multilib --disable-nls
--enable-languages=c,c++,ada --build=x86_64-apple-darwin15
Thread model: posix
gcc version 8.0.1 20180121 (experimental) (GCC) 

and failure happens on Darwin 17 as well as 15 (I don’t have a Darwin 16
machine).
Failure happens the same way when building Ada programs.