[PATCH] D93755: [VE][isel] Map EVT vectors to vector registers.

[Simon Moll via Phabricator via llvm-commits]

simoll added inline comments.


================
Comment at: llvm/lib/CodeGen/TargetLoweringBase.cpp:941
+  // Fully customized legalization.
+  Optional<LegalizeKind> CustomLK = getCustomTypeConversion(Context, VT);
+  if (CustomLK)
----------------
efriedma wrote:
> getTypeConversion is pretty closely tied to the conversions we actually support in type legalization.  I'm not sure it's a good idea to let the target completely override the logic here.  If there's some specific aspect of this function you'd like to customize, we can look at adding a more specific hook.
`getCustomTypeConversion` returns a `LegalizeKind` with limited options for legalization strategies  - we could even type check `LegalizeKind` in its constructor and assert if an illegal/unimplemented legalization step is attempted.

The fundamental issue with calling back from `getTypeConversion` is that it tries to peg all legalization steps to MVTs. That breaks down as soon as the intermediate step of legalization can only be an EVT. For example:

`v17i17 -> v17i32 -> v256i32`


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D93755/new/

https://reviews.llvm.org/D93755