AVX and AVX2 are pretty awful because of lane-crossing limitations, but AVX512 is actually really nice and feels like a real programmer designed it rather than an electrical engineer.
Yeah — my favorite instructions he added were `fmad233` and `faddsets`; the former instruction essentially bootstraps the line-equation for the mask-generation for rasterization, and the latter lets you 'step' the intersection. You could plumb the valid mask through and get the logical intersection "for free". This let us compute the covering mask in 9 + N instructions for N+1 4x4 tiles. We optimized tile load-store to work in 16x16 chunks, so valid mask generation came to just 24 cycles. It was my argument that using Boustrophedon order and just blasting the tile (rather than quad-tree descent like he designed) is what convinced him to let me work with RAD & do the non-polygon path for LRB.
Most Intel ISA extensions come from either customers asking for specific instructions, or from Intel engineers (from the hardware side) proposing reasonable extensions to what already exists.
LRBni, which eventually morphed into AVX-512, was developed by a team mostly consisting of programmers without long ties to Intel hw side, as a greenfield project to make an entirely new vector ISA that should be good from the standpoint of a programmer. I strongly feel that they have succeeded, and AVX-512 is transformative when compared to all previous Intel vector extensions.
The downside is that as they had much less input and restraint from the hw side, it's kind of expensive to implement, especially in small cores. Which directly led to its current market position.
gpderetta|2 years ago
[1] https://en.wikipedia.org/wiki/Michael_Abrash [2] https://www.anandtech.com/show/2580/9
thechao|2 years ago
Tuna-Fish|2 years ago
Most Intel ISA extensions come from either customers asking for specific instructions, or from Intel engineers (from the hardware side) proposing reasonable extensions to what already exists.
LRBni, which eventually morphed into AVX-512, was developed by a team mostly consisting of programmers without long ties to Intel hw side, as a greenfield project to make an entirely new vector ISA that should be good from the standpoint of a programmer. I strongly feel that they have succeeded, and AVX-512 is transformative when compared to all previous Intel vector extensions.
The downside is that as they had much less input and restraint from the hw side, it's kind of expensive to implement, especially in small cores. Which directly led to its current market position.