[Bug ipa/63533] New: Function splitter causes unnecessary splits

[y.gribov at samsung dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63533

            Bug ID: 63533
           Summary: Function splitter causes unnecessary splits
           Product: gcc
           Version: 5.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: ipa
          Assignee: unassigned at gcc dot gnu.org
          Reporter: y.gribov at samsung dot com
                CC: hubicka at gcc dot gnu.org, khlebnikov at openvz dot org,
                    ryabinin.a.a at gmail dot com

Created attachment 33712
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=33712&action=edit
Short repro

The attached reprocase contains an innocent function which can not ever benefit
from inlining. But fnsplit pass still jumps on it and splits it to two
functions thus hurting performance and code size:
 gcc -O2 -fconserve-stack -S repro.i -o-
 ...g.part.0:
 ...
 g:
 ...
     call    g.part.0
This can not be recovered later by inliner because of -fconserve-stack option.
The reprocase is a reduced version of a real-world code (from Linux kernel).