Re: GCC 8.3.0 vs. 9.0.1 - Mailing list pgsql-performance

From Andres Freund
Subject Re: GCC 8.3.0 vs. 9.0.1
Date
Msg-id 20190507174247.6s6qbmiwuzuoiaiz@alap3.anarazel.de
Whole thread Raw
In response to Re: GCC 8.3.0 vs. 9.0.1  (Peter Geoghegan <pg@bowt.ie>)
List pgsql-performance
Hi,

On 2019-05-07 10:28:16 -0700, Peter Geoghegan wrote:
> On Tue, May 7, 2019 at 10:06 AM Tom Lane <tgl@sss.pgh.pa.us> wrote:
> > 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.
> 
> Or a compiler bug. Link-time optimizations give the compiler a view of
> the program as a whole, not just a single TU at a time. This enables
> it to perform additional aggressive optimization.

Note that the flags described don't enable LTO.

Greetings,

Andres Freund



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