Stephen Hoffman<p>Why was Itanium code optimization so difficult for compilers?</p><p>The Itanium compiler optimizers just don't (and can't) know enough about the system memory and cache state. Among other (no pun intended) issues.</p><p>The attempts to improve out-of-order execution and related optimizations included providing run-time feedback into the executables; post-link, post-execution tuning. (HP Caliper / Atom / OM / etc.)</p><p><a href="https://www.cs.tufts.edu/comp/150PAT/tools/caliper/wiess-rev-4.pdf" rel="nofollow noopener noreferrer" translate="no" target="_blank"><span class="invisible">https://www.</span><span class="ellipsis">cs.tufts.edu/comp/150PAT/tools</span><span class="invisible">/caliper/wiess-rev-4.pdf</span></a></p><p>This DEC Alpha versus VLIW IA-64 Itanium paper from 1999 describes various issues with Itanium quite well too, for those interested in that part of history:</p><p><a href="https://web.archive.org/web/20010611202933/http://www.compaq.com/hpc/ref/ref_alpha_ia64.doc" rel="nofollow noopener noreferrer" translate="no" target="_blank"><span class="invisible">https://</span><span class="ellipsis">web.archive.org/web/2001061120</span><span class="invisible">2933/http://www.compaq.com/hpc/ref/ref_alpha_ia64.doc</span></a></p><p><a href="https://infosec.exchange/tags/digitalequipment" class="mention hashtag" rel="nofollow noopener noreferrer" target="_blank">#<span>digitalequipment</span></a> <a href="https://infosec.exchange/tags/alpha" class="mention hashtag" rel="nofollow noopener noreferrer" target="_blank">#<span>alpha</span></a> <a href="https://infosec.exchange/tags/itanium" class="mention hashtag" rel="nofollow noopener noreferrer" target="_blank">#<span>itanium</span></a> <a href="https://infosec.exchange/tags/compilers" class="mention hashtag" rel="nofollow noopener noreferrer" target="_blank">#<span>compilers</span></a> <a href="https://infosec.exchange/tags/optimization" class="mention hashtag" rel="nofollow noopener noreferrer" target="_blank">#<span>optimization</span></a> <a href="https://infosec.exchange/tags/retrocomputing" class="mention hashtag" rel="nofollow noopener noreferrer" target="_blank">#<span>retrocomputing</span></a></p>