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From: jgd@cix.co.uk (John Dallman)
Newsgroups: comp.os.vms
Subject: Re: Itanium support is back in GCC 15
Date: Mon, 24 Feb 2025 21:27 +0000 (GMT Standard Time)
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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