About

x264 is a critical benchmark for vectorization in the spec suite showing a roughly 2X improvement across many archtiectures once vector is enabled.  This work item is mean to track further improvements that may be possible in the benchmark through compiler improvements.

1. There is an arithmetic right shift followed by a masking operation in quant_4x4 that can be simplified into a logical right shift eliminating a small amount of code on a critical path.
2. Vector setup and element extraction is likely sub-optimal in the SAD/SATD routines. 
   1. Removal of VIEW_CONVERT_EXPR nodes is likely important
   2. And optimization of BITFIELD_INSERT_EXPR
3. Rearrangement of SLP nodes with multiple occurrences in the in the same statement to avoid duplicates with a vec_perm to restore the original ordering may have as much as a 10% benefit for vectorized x264.
   1. Additional information from GCC's bug database
   2. Proposed patch, probably won't go in as-is, but can be used for experimentation

Stakeholders/Partners

RISE:

Ventana: Robin Dapp

Ventana: Jeff Law

External:

                     VRULL:  Manolis Tsamis

Dependencies

Status

Updates

05 Jun 2024  

• Project reported as a priority for 2H2024, broken out from original effort