Stream: git-wasmtime

Topic: wasmtime / PR #3600 aarch64: Migrate `uextend`/`sextend` ...

Wasmtime GitHub notifications bot (Dec 14 2021 at 15:03):

alexcrichton opened PR #3600 from isle-5-uextend-sextend to main:

This commit migrates the sign/zero extension instructions from
lower_inst.rs to ISLE. There's actually a fair amount going on in this
migration since a few other pieces needed touching up along the way as
well:

• First is the actual migration of uextend and sextend. These
  instructions are relatively simple but end up having a number of special
  cases. I've attempted to replicate all the cases here but
  double-checks would be good.

• This commit actually fixes a few issues where if the result of a vector
  extraction is sign/zero-extended into i128 that actually results in
  panics in the current backend.

• This commit adds exhaustive testing for
  extension-of-a-vector-extraction is a noop wrt extraction.

• A bugfix around ISLE glue was required to get this commit working,
  notably the case where the RegMapper implementation was trying to
  map an input to an output (meaning ISLE was passing through an input
  unmodified to the output) wasn't working. This requires a mov
  instruction to be generated and this commit updates the glue to do
  this. At the same time this commit updates the ISLE glue to share more
  infrastructure between x64 and aarch64 so both backends get this fix
  instead of just aarch64.

Overall I think that the translation to ISLE was a net benefit for these
instructions. It's relatively obvious what all the cases are now unlike
before where it took a few reads of the code and some boolean switches
to figure out which path was taken for each flavor of input. I think
there's still possible improvements here where, for example, the
put_in_reg_{s,z}ext64 helper doesn't use this logic so technically
those helpers could also pattern match the "well atomic loads and vector
extractions automatically do this for us" but that's a possible future
improvement for later (and shouldn't be too too hard with some ISLE
refactoring).

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Wasmtime GitHub notifications bot (Dec 14 2021 at 15:03):

alexcrichton requested fitzgen for a review on PR #3600.

Wasmtime GitHub notifications bot (Dec 14 2021 at 21:51):

fitzgen submitted PR review.

Wasmtime GitHub notifications bot (Dec 14 2021 at 21:51):

fitzgen merged PR #3600.

Last updated: Dec 23 2024 at 12:05 UTC