Commits on Mar 19, 2024

1. [BasicCABI] Pass compiler-rt 128-bit return values in memory …

   Currently our LLVM Wasm backend returns 128-bit values as two `i64`s in
   case multivalue is enabled:
   https://github.com/llvm/llvm-project/blob/a5f576e5961ecc099bd7ccf8565da090edc84b0d/llvm/lib/Target/WebAssembly/WebAssemblyRuntimeLibcallSignatures.cpp#L697-L700
   
   But given that neither emscripten nor wasm-sdk seem to provide a
   multivalue version of compiler-rt, it looks this has not been working so
   far and the reason we haven't heard complaints was likely that no one
   was using compiler-rt with multivalue enabled.
   
   Maintaining and providing two different versions of compiler-rt is a
   cumbersome thing for toolchains, and emscripten already has to provide
   multiple versions of many libraries (e.g. threaded vs. non-threaded,
   debug vs. release, exception-enabled vs. disabled, ...).
   
   Also enabling the multivalue return on several compiler-rt functions
   that have a 128-bit return value wouldn't affect performance in a
   meaningful way, given that there are not many of them.
   
   I had a chance to chat with several people who contribute here offline
   this morning, and it looked we agreed that there is not much benefit to
   enabling multivalue return in compiler-rt functions. One thing I'm not
   sure is whether we decided to disable 128-bit multivalue returns for
   only compiler-rt functions or for all user functions. This PR currently
   says we do that only for compiler-rt; please let me know if you think we
   should do otherwise.

   

   aheejin committed Mar 19, 2024
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