Re: GCC 8.3.0 vs. 9.0.1

Steven Winfield <Steven(dot)Winfield(at)cantabcapital(dot)com> writes:
> A few days ago a blog post appeared on phoronix.com[1] comparing GCC 8.3.0 against 9.0.1 on Intel cascadelake processors.
> A notable difference was seen in the PostgreSQL benchmark (v10.3, pgbench, read/write, more detail below), both when compiling with -march=native and -march=skylake:
> I'm interested to know the devs' take on this is - does GCC 9 contain some new feature(s) that are particularly well suited to compiling and optimising Postgres? Or was GCC 8 particularly bad?

Given the described test setup, I'd put basically no stock in these
numbers. It's unlikely that this test case's performance is CPU-bound
per se; more likely, I/O and lock contention are dominant factors.
So I'm afraid whatever they're measuring is a more-or-less chance
effect rather than a real system-wide code improvement.

It is an interesting report, all the same.

regards, tom lane