Cranelift: Incorrect abi for i128, i128 return value on x86_64 sysv

[bjorn3]

Expected Results

All return values are returned using a single return pointer.

Actual Results

Return values are put into registers where possible and on the stack for the rest.

Versions and Environment

Cranelift version or commit: 0.111

Operating system: Linux

Architecture: x86_64

Extra Info

This is one of the causes for rust-lang/rustc_codegen_cranelift#1525. The same issue may exist on aarch64 and other archs too, but haven't checked yet.

[bjorn3]

PR's opened while working on this:

• Couple of cleanups to the ABI computation #9253
• Remove StructArgument support from the arm64, riscv64 and s390x backends #9258
• Couple of improvements to the abi handling code (part 3) #9267
• Couple of improvements to the abi handling code (part 4) #9284
• Make the Tail call conv follow the system call conv for the return area ptr #9287

[bjorn3]

Found another issue: The x86_64 and riscv64 backends add an implicit return pointer after all other arguments rather than as first argument.

Edit: Fixed in #9267