e3c57fdd84
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'). It isn't explicitly noted in the RISC-V psABI, but arrays of empty records will disqualify a struct for consideration of using the FP calling convention in g++. This patch matches that behaviour. The psABI issue <https://github.com/riscv-non-isa/riscv-elf-psabi-doc/issues/358> seeks to clarify this. This patch was previously committed but reverted after a bug was found. This recommit adds additional logic to prevent that bug (adding an extra check for when a candidate from detectFPCCEligibleStructHelper may not be valid). Differential Revision: https://reviews.llvm.org/D142327
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