Commits on Apr 12, 2024

1. [WebAssembly] Enable multivalue return when multivalue ABI is used …

   Multivalue feature of WebAssembly has been standardized for several
   years now. I think it makes sense to be able to enable it in the feature
   section by default for our clang/llvm-produced binaries so that the
   multivalue feature can be used as necessary when necessary within our
   toolchain and also when running other optimizers (e.g. wasm-opt) after
   the LLVM code generation.
   
   But some WebAssembly toolchains, such as Emscripten, do not provide
   both mulvalue-returning and not-multivalue-returning versions of
   libraries. Also allowing the uses of multivalue in the features section
   does not necessarily mean we generate them whenever we can to the
   fullest, which is a different code generation / optimization option.
   
   So this makes the lowering of multivalue returns conditional on the use
   of 'experimental-mv' target ABI. This ABI is turned off by default and
   turned on by passing `-Xclang -target-abi -Xclang experimental-mv` to
   `clang`, or `-target-abi experimental-mv` to `clang -cc1` or `llc`.
   
   But the purpose of this PR is not tying the multivalue lowering to this
   specific 'experimental-mv'. 'experimental-mv' is just one multivalue ABI
   we currently have, and it is still experimental, meaning it is not very
   well optimized or tuned for performance. (e.g. it does not have the
   limitation of the max number of multivalue-lowered values, which can be
   detrimental to performance.) We may change the name of this ABI, or
   improve it, or add a new multivalue ABI in the future. Also I heard that
   WASI is planning to add their multivalue ABI soon. So the plan is,
   whenever any one of multivalue ABIs is enabled, we enable the lowering
   of multivalue returns in the backend. We currently have only
   'experimental-mv' in the repo so we only check for that in this PR.
   
   Related past discussions:
    llvm#82714
   WebAssembly/tool-conventions#223 (comment)

   

   aheejin committed Apr 12, 2024
   Configuration menu

   • View commit details
   • Copy full SHA for 6ecbb86
   • Browse repository at this point

   Copy the full SHA

   6ecbb86 View commit details

   Browse the repository at this point in the history