Re: Itanium support is back in GCC 15

On 2/24/2025 4:27 PM, John Dallman wrote:

In article <vpi9sr$19atf$1@dont-email.me>, seaohveh@hoffmanlabs.invalid
(Stephen Hoffman) wrote:
 

The Itanium compiler optimizer just doesn't (and can't) know enough
about the system memory state, yes. Among other (no pun intended)
issues.
>
The attempt to address that included providing run-time feedback
into the executables; providing post-link, post-execution tuning.
(Caliper / Atom / OM / etc.)

 "Attempt" is about right.
 I did several years porting work to Itanium. I tried run-time feedback
zero times: doing the link of the instrumented build took over an hour,
up from about a minute, because it was doing all the code generation at
link time.
 The claim was "you only do this for the build you'll ship." My response
was "The compiler is so immature that I'm reporting new bugs every week,
and you want me to give the compiler new and difficult challenges?"
 I never heard of anyone who got anywhere with profile-guided optimisation
on Itanium. Have you?
 John

Actually, the NonStop Itanium kernel is built using PGO.  Apparently, for their test workload of transactions, the savings was a measurable "few" percent.  [I think in the 3-5% range but I'm not sure anymore]