[PATCH] D79806: [CodeGen][SVE] Specify meaning of EXTRACT_SUBVECTOR for scalable vectors

[Eli Friedman via Phabricator via llvm-commits]

efriedma added a reviewer: craig.topper.
efriedma added a comment.

Both the scaled and unscaled variations are potentially useful.  But the scaled variation is probably more useful, and it's probably a lot less work to use the names INSERT_SUBVECTOR and EXTRACT_SUBVECTOR for the scaled version.  So this probably makes sense.

I think I'd rather use a different opcode for the cases where you're mixing fixed/scalable vectors.  There are some potentially weird edge cases to deal with there, and the existing code is much more likely to blow up. For example, can you extract an `<8 x i32>` from a `<vscale x 4 x i32>`?  Does it matter if we know that vscale is 2 or more for the current subtarget?

While we're looking at this, the "potentially variable" part is very messy, and it looks like nothing actually takes advantage of it.  Posted https://reviews.llvm.org/D79814 .

While you're in ISDOpcodes, can you add notes to various other vector-specific operations?  Probably BUILD_VECTOR and VECTOR_SHUFFLE should always return fixed vectors, and the behavior of INSERT_VECTOR_ELT/EXTRACT_VECTOR_ELT/CONCAT_VECTORS/VSELECT should be clear.  But better to note it explicitly, I think.


CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D79806/new/

https://reviews.llvm.org/D79806