GeezerVison

corona10 left a comment

corona10 left a comment

(This change is a quick and dirty way to merge some of the build system
improvements I'm proposing in pythongh-101093 before the 3.12 feature freeze.
I wanted to scope bloat myself to fix some longstanding deficiencies in
the build system around profile-guided builds. But I'm getting soft
resistance to the reviews so close to the freeze deadline and it is
obvious that we need a simpler solution to hit the 3.12 deadline. While
this change is quick and dirty, it attempts to not make things worse.)

Before this change, we only applied bolt to the main python binary.
After this change, we apply bolt to libpython if it is configured. In
shared library builds, most of the C code is in libpython so it is
critical to apply bolt to libpython to realize bolt benefits.

This change also reworks how bolt instrumentation is applied. It
effectively removes the readelf based logic added in pythongh-101525 and
replaces it with a mechanism that saves a copy of the pre-bolt binary
and restores that copy when necessary. This allows us to perform
bolt optimizations without having to manually delete the output binary
to force a new bolt run.

We also add a new make target for purging bolt files and hook it up
to `clean` so bolt state is purged when appropriate.

`.gitignore` rules have been added to ignore files related to bolt.

Before and after this refactor, `make` will no-op after a previous run.
Both versions should also share common make DAG deficiencies where
targets fail to trigger as often as they need to or can trigger
prematurely in certain scenarios. e.g. after this change you may need
to `rm profile-bolt-stamp` to force a bolt run because there aren't
appropriate non-phony targets for bolt's make target to depend on.
Fixing this is a non-trivial amount of work that will likely have to
wait until the 3.13 window.

To make it easier to iterate on custom BOLT settings, the flags to
pass to instrumentation and application are now defined in configure
and can be overridden by passing `BOLT_INSTRUMENT_FLAGS` and
`BOLT_APPLY_FLAGS`.

erlend-aasland left a comment