[PATCH] D152722: [llvm] Intoduce llvm-orderfile

[Ellis Hoag via Phabricator via llvm-commits]

ellis added a comment.

I'm happy to see that there is interest in order files! Recently, I've been developing order file generation within IRPGO that is understood by the `llvm-profdata` tool. In short, you can instrument a binary to get function traces, merge them into a profile, and then use the `llvm-profdata` tool to compute a function order which you can pass to the linker using `-symbol-ordering-file`.

  $ clang -fprofile-generate -mllvm -pgo-temporal-instrumentation main.cpp
  $ ./a.out
  $ llvm-profdata merge default.profraw -o default.profdata
  $ llvm-profdata order default.profdata -o order.txt

Please see https://discourse.llvm.org/t/rfc-temporal-profiling-extension-for-irpgo/68068 for details on that.

When combined with Lightweight Instrumentation <https://discourse.llvm.org/t/instrprofiling-lightweight-instrumentation/59113>, this is more lightweight (at runtime), has better infra support, has more features, and should give better performance than `-forder-file-instrumentation`. In fact, I plan to deprecate `-forder-file-instrumentation` now that the initial work on temporal instrumentation is done.

Please don't hesitate to reach out on discord or discourse if you have questions :)


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https://reviews.llvm.org/D152722