> Q: I feel like deja vu - at Hot Chips, Intel introduced VLIW-concept Itanium that pushed complexity onto the compiler. I see traces of that here. What are you doing to avoid the Itanium traps? How will you avoid IP from Intel?
> A: Itanium was in-order VLIW, hope people will build compiler to get perf. We came from opposite direction - we use dynamic scheduling. We are not VLIW, every node defines sub-graphs and dependent instructions. We designed the compiler first. We build hardware around the compiler, Intel approach the opposite.
That captures a lot of my take on Itanium at the time: despite being "VLIW" it took on what at the time was a vast amount of CPU controller complexity without an obvious design win or clear high-performance compilation model. As an outsider, it felt like an extremum of Intel's flavor of design hubris.
It's interesting to compare the Itanium's approach to a VLIW contemporary from TI: the C6x VLIW DSP ISA. The C6x ISA took on very little controller complexity. Instead, it exposed a very clear operational and optimization model for the VLIW instruction blocks. An optimizing compiler did a decent first-step job at generating code. That was complemented by clear documentation of the optimization workflow, from compiler-stage iteration down to good guidance on the nuts and bolts of hand-optimizing. By comparison, IA64 was just ... a big head-scratching moment all around. I never got to work with C6x code professionally, but dang it looked like a blast to code and optimize for.
Well, why not.
> Q: I feel like deja vu - at Hot Chips, Intel introduced VLIW-concept Itanium that pushed complexity onto the compiler. I see traces of that here. What are you doing to avoid the Itanium traps? How will you avoid IP from Intel?
> A: Itanium was in-order VLIW, hope people will build compiler to get perf. We came from opposite direction - we use dynamic scheduling. We are not VLIW, every node defines sub-graphs and dependent instructions. We designed the compiler first. We build hardware around the compiler, Intel approach the opposite.
https://www.anandtech.com/show/13255/hot-chips-2018-tachyum-...