EPIC failure (to cancel the project when it was first failing)

EPIC failure (to cancel the project when it was first failing)

1. I don't think that compiler technology that benefitted IA-64 would have benefitted OoO IA-32 implementations much, for the following reasons: Techniques like basic block instruction scheduling, superblock scheduling, and modulo scheduling (software pipelining) were already known at the time of the Pentium, and the in-order Pentium would have benefitted more from it than the Pentium Pro. However, these techniques tend to increase the register pressure (IA-64 has 128 integer registers for a reason), and IA-32 has only 8 registers, so applying such techniques could have easily resulted in a slowdown.

   IA-64 also has architectural features for speculation and for dealing with aliases that IA-32 does not have and so an IA-32 compiler cannot not use. But given the lack of registers, that's moot.

2. Every CPU profits from more cache for applications that need it (e.g., see the Ryzen 5800X3D), and given main memory latencies of 100 cycles and more, the benefit of OoO execution for that is limited (at that time, but also now). Itanium (II) got large caches, because a) that's what HP's customer's were used to and b) because even outside HP the initial target market was high end stuff. Also, given all the promises about superior performance, cache is an easy way to get it on applications that benefit from cache (and if you skimp on it, it's an easy way to make your architecture look bad in certain benchmarks). So Itanium II (not sure about Itanium) could score at least a few benchmark wins, and its advocates could say: "See, that's what we promised. And when compilers improve, we will also win the rest."