[Bug lto/64860] [5 Regression] multiple definition of typeinfo in 5.0 (4.9.2 works)

[hubicka at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64860

--- Comment #8 from Jan Hubicka <hubicka at gcc dot gnu.org> ---
Created attachment 35100
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=35100&action=edit
partial patch

Hi,
this is a patch that adds necessary checks into resolution code. Basically if
static linking is anticipated, we can not derive much of useful info from
PREVAILING_DEF/PREVAILING_DEF_IRONLY_EXP and must anticipate that static
linking may change these and drop comdat groups.

THe catch is that someone needs to pass -r to lto1 that is not currently
happening (I verified that if I hack opts.c to set incremental_linking to true
the testcase works).

With -r option, I can imagine that lto-wrapper can do it, because we get:
COLLECT_GCC_OPTIONS='-c' '-fmath-errno' '-fsigned-zeros' '-ftrapping-math'
'-fno-trapv' '-fno-openmp' '-fno-openacc' '-mtune=generic' '-march=x86-64'
'-O2' '-B' './' '-O2' '-r' '-v' '-mtune=generic' '-march=x86-64'
'-fltrans-output-list=/tmp/cc3o3UIr.ltrans.out' '-fwpa'
'-fresolution=/tmp/cchYXuvF.res

I donot know hwere -r gets dropped though.  But the testcase uses -Wl,-r that
may need LTO plugin extension?