a87be980d8
llvm: migrate to new parameter-bearing uwtable attr In https://reviews.llvm.org/D114543 the uwtable attribute gained a flag so that we can ask for sync uwtables instead of async, as the former are much cheaper. The default is async, so that's what I've done here, but I left a TODO that we might be able to do better. While in here I went ahead and dropped support for removing uwtable attributes in rustc: we never did it, so I didn't write the extra C++ bridge code to make it work. Maybe I should have done the same thing with the `sync|async` parameter but we'll see.
The codegen crate contains the code to convert from MIR into LLVM IR,
and then from LLVM IR into machine code. In general it contains code
that runs towards the end of the compilation process.
For more information about how codegen works, see the rustc dev guide.