bash error handling and reporting is atrocious. Without -e it will
just ignore errors. With -e it will stop on errors, but not report
where the error happened (apart from exiting itself with an error code).
Improve that with the `trap ERR` command. Note that this won't be invoked
on intentional error exit with `exit 1`.
We apply this on every bash script that contains -e or that it appears
trivial to set it in. Non-trivial scripts without -e are left unmodified,
since they might intentionally invoke failing scripts.
Closesscylladb/scylladb#22747
This commit enables profile-guided optimizations (PGO) in the Scylla build.
A full LLVM PGO requires 3 builds:
1. With -fprofile-generate to generate context-free (pre-inlining) profile. This
profile influences inlining, indirect-call promotion and call graph
simplifications.
2. With -fprofile-use=results_of_build_1 -fcs-profile-generate to generate
context-sensitive (post-inlining) profile. This profile influences post-inline
and codegen optimizations.
3. With -fprofile-use=merged_results_of_builds_1_2 to build the final binary
with both profiles.
We do all three in one ninja call by adding release-pgo and release-cs-pgo
"stages" to release. They are a copy of regular release mode, just with the
flags described above added. With the full course, release objects depend on the
profile file produced by build/release-cs-pgo/scylla, while release-cs-pgo
depends on the profile file generated by build/release-pgo/scylla.
The stages are orthogonal and enabled with separate options. It's recommended
to run them both for full performance, but unfortunately each one adds a full
build of scylla to the compile time, so maybe we can drop one of them in the
future if it turns out e.g. that regular PGO doesn't have a big effect.
It's strongly recommended to combine PGO with LTO. The latter enables the entire
class of binary layout optimizations, which for us is probably the most
important part of the entire thing.
