[PATCH] D82663: [CodeGen] Have CodeGen for fixed-point unsigned with padding emit signed operations.

[John McCall via Phabricator via cfe-commits]

rjmccall added a comment.

Would it be sensible to use a technical design more like what the matrix folks are doing, where LLVM provides a small interface for emitting operations with various semantics?  FixedPointSemantics would move to that header, and Clang would just call into it.  That way you get a lot more flexibility in how you generate code, and the Clang IRGen logic is still transparently correct.  If you want to add intrinsics or otherwise change the IR patterns used for various operations, you don't have to rewrite a bunch of Clang IRGen logic every time, you just have to update the tests.  It'd then be pretty straightforward to have internal helper functions in that interface for computing things like whether you should use signed or unsigned intrinsics given the desired FixedPointSemantics.

My interest here is mainly in (1) keeping IRGen's logic as obviously correct as possible, (2) not hard-coding a bunch of things that really feel like workarounds for backend limitations, and (3) not complicating core abstractions like FixedPointSemantics with unnecessary extra rules for appropriate use, like having to pass an extra "for codegen" flag to get optimal codegen.  If IRGen can just pass down the high-level semantics it wants to some library that will make intelligent decisions about how to emit IR, that seems best.


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D82663/new/

https://reviews.llvm.org/D82663