[Bug tree-optimization/84443] New: powerpc suboptimal code generation (shrink wrap unlikely path) for Linux spinlocks

[npiggin at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=84443

            Bug ID: 84443
           Summary: powerpc suboptimal code generation (shrink wrap
                    unlikely path) for Linux spinlocks
           Product: gcc
           Version: 8.0.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: npiggin at gmail dot com
  Target Milestone: ---

Created attachment 43452
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=43452&action=edit
testcase with comment at the top describing desired output

A small fast path code gets several non-volatile registers saved on stack, and
a sub-optimal restore in the return path.

The example is derived from (but not identical to) the Linux kernel spinlock
implementation.

Tested with gcc version 8.0.1 20180207 (experimental) [trunk revision 257435]
(Debian 8-20180207-2).