[RISCV][GlobalISel] Add lowerFormalArguments for calling convention

[nitinjohnraj]

Summary

This patch adds an IncomingValueHandler and IncomingValueAssigner, and implements minimal support for lowering formal arguments according to the RISC-V calling convention. Simple non-aggregate integer and pointer types are supported.

In the future, we must correctly handle byval and sret pointer arguments, and instances where the number of arguments exceeds the number of registers.

[lewis-revill]

Rebase, update test structure.

[Joe]

llvm/lib/Target/RISCV/RISCVCallLowering.cpp

171 ↗

(On Diff #248480)

Perhaps add a test for this?

173 ↗

(On Diff #248480)

Floats don't work here. HandleAssignments tries to truncate it. Best to leave it unsupported for now.

[lewis-revill]

Address comments relating to supported types.

[lewis-revill]

Rebased, and updated where appropriate to continue to build correctly.

[arsenm]

llvm/lib/Target/RISCV/RISCVCallLowering.cpp

184 ↗

(On Diff #399995)

Same as other patches, don't copy your own splitToValueTypes

[lewis-revill]

Introduce an IncomingValueAssigner to allow us to call determineAndHandleAssignments.

[arsenm]

llvm/test/CodeGen/RISCV/GlobalISel/irtranslator/args.ll

258

Probably should have some byval, sret, and cases where the argument list runs out of registers. Same for return values / hidden sret

[nitinjohnraj]

Rebased

[nitinjohnraj]

Updated parent revision

llvm/test/CodeGen/RISCV/GlobalISel/irtranslator/args.ll

258

Probably should have some byval, sret,

Correct me if I'm wrong, but byval and sret both require support for aggregate types, which this patch doesn't support.

sret, and cases where the argument list runs out of registers.

Do you have an example of a similar test? I wasn't aware that we could run out of registers at this phase, I thought that we could have an unlimited number of virtual registers.

[arsenm]

llvm/test/CodeGen/RISCV/GlobalISel/irtranslator/args.ll

258

This is wrong. sret and byval do not really have anything to do with aggregate types, and apply to pointers. You see them on a pointer argument, not aggregate. They would typically be used with an aggregate in memory type, but the in-memory type can be anything

You're mapping to an ABI constraint. If you had 4 32-bit registers for argument passing, you would run out of argument passing registers and have one stack passed argument for (i32, i32, i32, i32, i32).

[tschuett]

I am blind. Was there an opaque pointer test?

[arsenm]

llvm/test/CodeGen/RISCV/GlobalISel/irtranslator/args.ll

234

Should only have opaque pointers

[tschuett]

Could you also add a test with^TM too many arguments.

[arsenm]

In D74977#4361352, @tschuett wrote:

Could you also add a test with^TM too many arguments.

A variety of types in the excess region would also be good. There can be bugs in the memory vs register type

[craig.topper]

llvm/lib/Target/RISCV/GISel/RISCVCallLowering.cpp

217

Use single space after //

[nitinjohnraj]

Used opaque pointers, added tests for byval and sret

[nitinjohnraj]

llvm/test/CodeGen/RISCV/GlobalISel/irtranslator/args.ll

258

Thanks for the detailed feedback! I have added tests for sret and byval; however, this patch doesn't currently handle them correctly, I suspect. I'm referring to SelectionDAG for RISCV to figure out how to support them, but I plan to add them in an upcoming patch.

I have not added a test for when we run out of argument passing registers, as it requires the implementation of getStackAddress. That'll be added in an upcoming patch as well.