xry111 added a comment. In D151298#4367496 <https://reviews.llvm.org/D151298#4367496>, @xry111 wrote:
> In D151298#4367458 <https://reviews.llvm.org/D151298#4367458>, @wangleiat > wrote: > >>> I think the paragraph means: >>> >>> class Empty {}; >>> int test(Empty empty, int a); >>> >>> Then we should put `a` into `a1`, not `a0`. And we are indeed doing so. >> >> yes. with this patch, `a` will be passed with `a1` register. >> >>> I mean now GCC and Clang have the same behavior, so it's easier to just >>> document the behavior in our psABI doc instead of making both Clang and GCC >>> rigidly following the interpretation of psABI (which is currently unclear >>> about zero-sized fields now) anyway. >>> >>> And the current behavior of GCC and Clang treating a class containing two >>> floating-point members and some empty fields is same as RISC-V, so it's >>> highly unlikely we are violating the C++ standard or IA64 C++ ABI (or the >>> entire RISC-V ecosystem would be violating them). The only issue is our >>> psABI is unclear about empty fields, and the easiest way to solve the issue >>> is revising the psABI (maybe, just "borrowing" some paragraphs from RISC-V >>> psABI if there is no copyright issue). >> >> If we want to ignore empty structures, it is not enough to only modify >> psABI, because the current implementations of gcc and clang do not ignore >> empty structures in all cases. For example: >> >> struct { struct{}; int i; }; // in this case, the empty struct is not >> ignored. >> struct { struct{}; float f; }; // ignored. > > This is the same behavior as RISC-V. While attempting to pass a struct > through FPRs, the empty field is ignored. But if passing through FPR does > not work and it's passed through GPRs, the empty fields are not ignored: > > https://godbolt.org/z/T1PKoxbYM > >> Whether to ignore empty structures or not can affect the testing of gdb. >> @seehearfeel knows more details. > > I guess we should be able to fix it for GDB because they must have fixed it > for RISC-V already. @seahearfeel: https://sourceware.org/git/?p=binutils-gdb.git;a=commit;h=9f0272f8548164b024ff9fd151686b2b904a5d59 Repository: rG LLVM Github Monorepo CHANGES SINCE LAST ACTION https://reviews.llvm.org/D151298/new/ https://reviews.llvm.org/D151298 _______________________________________________ cfe-commits mailing list cfe-commits@lists.llvm.org https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits
