Introduces a variant of size-hint multi-kernel, where for novel runtime shapes, instead of performing full benchmarking to determine the optimal kernel, selects one of many kernels pre-generated from multi-kernel hints, based off similarity b/w hint / runtime input & output shapes (L1 distance in log2 space).
Some caveats/changes:
- Size-hint multi-kernel now only kicks in if the kernel has dynamic shapes
- Pre-generation still only does 1-d search over specified hints, e.g. `matmul([s0, s1], [s1, s2])` with size-hints `[64, 256]` only generates 2 kernels - based on tuning shapes ([64, 64], [64, 64]) and ([256, 256], [256, 256]). Extending this to reasonable n-d search (via user API?) is an extension
Benchmarking results, compared to multi-kernel w/ full benchmarking (hints 64, 4096), and compiling with the ground truth hint:
<img width="1902" height="1222" alt="550541081_1088709150049684_6528797079439730237_n" src="https://github.com/user-attachments/assets/056cca48-c16a-4451-9b4a-fa13a7a058a9" />
Full benchmarking doing worse is extremely weird, but we did see similar spikes in #156628
Pull Request resolved: https://github.com/pytorch/pytorch/pull/163090
Approved by: https://github.com/bobrenjc93
2a9745de3c