It prevents LLVM from being linked with LLD at least on Windows, with
errors like this:
```
= note: ld.lld: error: duplicate symbol: vtable for llvm::FormalArgHandler
>>> defined at librustc_llvm-a81737dd65a7c126.rlib(M68kCallLowering.cpp.obj)
>>> defined at librustc_llvm-a81737dd65a7c126.rlib(PPCCallLowering.cpp.obj)
```
Binutils linker also complains about this, but only with warnings.
`FormalArgHandler` has a base class `M68kIncomingValueHandler` which
doesn't have a virtual method `markPhysRegUsed` like
`IncomingValueHandler`s for all other targets including PPC, so it
results in a conflict.
The simplest fix is to rename the `FormalArgHandler` structure (rather
than to add virtual methods for compatibility).
cc https://github.com/rust-lang/rust/issues/107668
Previously they were passed by non-const reference. No in tree target
modifies the values.
This makes it possible to call assignValueToAddress from
assignCustomValue without a const_cast. For example in this patch
https://github.com/llvm/llvm-project/pull/69138.
The term "next stack offset" is misleading because the next argument is
not necessarily allocated at this offset due to alignment constrains.
It also does not make much sense when allocating arguments at negative
offsets (introduced in a follow-up patch), because the returned offset
would be past the end of the next argument.
Reviewed By: arsenm
Differential Revision: https://reviews.llvm.org/D149566
This patch implements CallLowering::lowerCall based on M68k calling
convention and adds M68kOutgoingValueHandler and CallReturnHandler to
handle argument passing and returned value.
