efriedma added inline comments.
================ Comment at: clang/lib/Driver/ToolChains/Arch/AArch64.cpp:318 + if (Args.hasArg(options::OPT_ffixed_x0)) + Features.push_back("+reserve-x0"); ---------------- trong wrote: > trong wrote: > > phosek wrote: > > > trong wrote: > > > > What happens (should happen) if we reserve x0 and compile a function > > > > with a return value? > > > Clang throws `error: AArch64 doesn't support function calls if any of the > > > argument registers is reserved.` as for any other argument register. > > Yes, if x0 is reserved, it can't be used to pass arguments. But what > > happens if x0 is used to return a value? For example: > > ``` > > int foo() { > > return 1; > > } > > ``` > > It would be helpful if compiling `foo()` with x0 reserved threw an error. > OTOH, [[ https://godbolt.org/z/jWW09Y | gcc ]] doesn't complain, so maybe > we're OK here. IIRC gcc never reports any errors for its version of these flags; that doesn't mean we should accept constructs which don't have defined behavior. I'd prefer to print an error in any situation where we would implicitly use a reserved register. Repository: rG LLVM Github Monorepo CHANGES SINCE LAST ACTION https://reviews.llvm.org/D56305/new/ https://reviews.llvm.org/D56305 _______________________________________________ cfe-commits mailing list cfe-commits@lists.llvm.org https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits