[all-commits] [llvm/llvm-project] 17a58b: [clang][RISCV] Fix ABI handling of empty structs w...

[Alex Bradbury via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: 17a58b3ca7ec18585e9ea8ed8b39d72fe36fb6cb
      https://github.com/llvm/llvm-project/commit/17a58b3ca7ec18585e9ea8ed8b39d72fe36fb6cb
  Author: Alex Bradbury <asb at igalia.com>
  Date:   2023-07-24 (Mon, 24 Jul 2023)

  Changed paths:
    M clang/docs/ReleaseNotes.rst
    M clang/lib/CodeGen/ABIInfoImpl.cpp
    M clang/lib/CodeGen/ABIInfoImpl.h
    M clang/lib/CodeGen/Targets/RISCV.cpp
    M clang/test/CodeGen/RISCV/abi-empty-structs.c

  Log Message:
  -----------
  [clang][RISCV] Fix ABI handling of empty structs with hard FP calling conventions in C++

As reported in <https://github.com/llvm/llvm-project/issues/58929>,
Clang's handling of empty structs in the case of small structs that may
be eligible to be passed using the hard FP calling convention doesn't
match g++. In general, C++ record fields are never empty unless
[[no_unique_address]] is used, but the RISC-V FP ABI overrides this.

After this patch, fields of structs that contain empty records will be
ignored, even in C++, when considering eligibility for the FP calling
convention ('flattening'). See also the relevant psABI issue
<https://github.com/riscv-non-isa/riscv-elf-psabi-doc/issues/358> which
seeks to clarify the documentation.

Fixes https://github.com/llvm/llvm-project/issues/58929

Differential Revision: https://reviews.llvm.org/D142327