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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
4. GCC does not make good use of widening vector ops that overlap source/destination registers.  Expectation is this is another 1-2% improvement
5. GCC does not hoist vxrm assignments aggressively, which can significantly impact performance if the uarch does not provide fast vxrm access.   This is about 2% on the BPI

Stakeholders/Partners

RISE:

Ventana: Robin Dapp

Ventana: Jeff Law – currently looking at vxrm hoisting

External:

                     VRULL:  Manolis Tsamis

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Updates

14 Aug 2024

• VRULL's patch has been upstreamed and we're seeing desired vectorization for the other loop in the SATD routines
• Note overlapping with widening ops and problems with vxrm hoisting improvement opportunities

05 Jun 2024  

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

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