[Bug rtl-optimization/96475] New: direct threaded interpreter with computed gotos generates suboptimal dispatch loop

[npiggin at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96475

            Bug ID: 96475
           Summary: direct threaded interpreter with computed gotos
                    generates suboptimal dispatch loop
           Product: gcc
           Version: 10.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: rtl-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: npiggin at gmail dot com
                CC: segher at gcc dot gnu.org
  Target Milestone: ---
            Target: powerpc64le-linux-gnu

Created attachment 48999
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=48999&action=edit
test case

The attached test case code generation with -O2 for run_program_goto generates
a central indirect branch dispatch to handlers that branch back to the central
dispatcher.

Direct threaded code with indirect branches between handlers is faster on a
POWER9 when there are no branch mispredictions due to fewer branches, and it
should generally do better with branch prediction when there is an indirect
branch from each handler.