[Bug target/86449] New: GCC 8 compiler generates slower code for spec 2006 calculix on a power9 using -mcpu=power9 than using -mcpu=power8

[meissner at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=86449

            Bug ID: 86449
           Summary: GCC 8 compiler generates slower code for spec 2006
                    calculix on a power9 using -mcpu=power9 than using
                    -mcpu=power8
           Product: gcc
           Version: 8.1.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: target
          Assignee: unassigned at gcc dot gnu.org
          Reporter: meissner at gcc dot gnu.org
  Target Milestone: ---

I ran spec 2006 on a DD2.2 power9, and I noticed the GCC 8.x branch (subversion
id 26248) generated slower code for calculix when compiled with a -mcpu=power9
option instead of -mcpu=power8.

Note, the trunk actually generates 2% faster code for -mcpu=power9 than for
-mcpu=power8.  This issue is only a regression on the GCC 8 branch.