[PATCH] D60456: [RISCV][WIP/RFC] Hard float ABI support

[Alex Bradbury via Phabricator via cfe-commits]

asb created this revision.
asb added a reviewer: rjmccall.
Herald added subscribers: benna, psnobl, jocewei, PkmX, rkruppe, the_o, brucehoult, MartinMosbeck, rogfer01, edward-jones, zzheng, jrtc27, shiva0217, kito-cheng, niosHD, sabuasal, apazos, simoncook, johnrusso, rbar.
Herald added a project: clang.

The RISC-V hard float calling convention <https://github.com/riscv/riscv-elf-psabi-doc/blob/master/riscv-elf.md#hardware-floating-point-calling-convention> requires the frontend to:

- Detect cases where, once "flattened", a struct can be passed using int+fp or fp+fp registers under the hard float ABI and coerce to the appropriate type(s)
- Track usage of GPRs and FPRs in order to gate the above, and to determine when signext/zeroext attributes must be added to integer scalars

This patch attempts to do this in compliance with the documented ABI, and uses ABIArgInfo::CoerceAndExpand in order to do this. @rjmccall, as author of that code I've tagged you as reviewer for initial feedback on my usage.

Note that a previous version of the ABI indicated that when passing an int+fp struct using a GPR+FPR, the int would need to be sign or zero-extended appropriately. GCC never did this <https://gcc.gnu.org/bugzilla/show_bug.cgi?id=86387> and the ABI was changed <https://github.com/riscv/riscv-elf-psabi-doc/pull/74>, which makes life easier as ABIArgInfo::CoerceAndExpand can't currently handle sign/zero-extension attributes.

I'm sharing just in case there are any concerns about this general approach. Known deficiencies in this patch are all related to testing:

- Needs more basic ilp32d/lp64f/lp64d tests
- Not enough coverage of bitfields in structs, packed+aligned structs etc


Repository:
  rC Clang

https://reviews.llvm.org/D60456

Files:
  lib/Basic/Targets/RISCV.h
  lib/CodeGen/TargetInfo.cpp
  test/CodeGen/riscv32-ilp32-ilp32f-abi.c
  test/CodeGen/riscv32-ilp32-ilp32f-ilp32d-abi.c
  test/CodeGen/riscv32-ilp32f-abi.c
  test/CodeGen/riscv32-ilp32f-ilp32d-abi.c

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