polyval: match ideal assembly #44
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The previous implementation used separate `#[target_feature(...)]` blocks for each `core::arch` intrinsic. This thwarts the inliner, so these all translated to `call` instructions. This change inlines the intrinsic calls into larger `#[target_feature(...)]`-gated functions. When compiling with `-C target-cpu=skylake`, the generated assembly matches the idealized version as described in this QuarksLab blog post: https://blog.quarkslab.com/reversing-a-finite-field-multiplication-optimization.html
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This was referenced Jul 26, 2023
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The previous implementation used separate
#[target_feature(...)]blocks for eachcore::archintrinsic. This thwarts the inliner, so these all translated tocallinstructions.This change inlines the intrinsic calls into larger
#[target_feature(...)]-gated functions.When compiling with
-C target-cpu=skylake, the generated assembly matches the idealized version (for at least the Montgomery fast reduction) as described in this QuarksLab blog post:https://blog.quarkslab.com/reversing-a-finite-field-multiplication-optimization.html
Their version:
Godbolt: https://godbolt.org/z/Zjuvwu