[Info-vax] Itanium support is back in GCC 15

[John Reagan]

On 2/24/2025 4:27 PM, John Dallman wrote:
> In article <vpi9sr$19atf$1 at dont-email.me>, seaohveh at 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]