https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102024
--- Comment #39 from CVS Commits <cvs-commit at gcc dot gnu.org> --- The master branch has been updated by Andreas Krebbel <kreb...@gcc.gnu.org>: https://gcc.gnu.org/g:bc79f0d9048375e402497d5f2ef457c9500310e4 commit r12-8277-gbc79f0d9048375e402497d5f2ef457c9500310e4 Author: Andreas Krebbel <kreb...@linux.ibm.com> Date: Wed Apr 27 09:20:41 2022 +0200 PR102024 - IBM Z: Add psabi diagnostics For IBM Z in particular there is a problem with structs like: struct A { float a; int :0; }; Our ABI document allows passing a struct in an FPR only if it has exactly one member. On the other hand it says that structs of 1,2,4,8 bytes are passed in a GPR. So this struct is expected to be passed in a GPR. Since we don't return structs in registers (regardless of the number of members) it is always returned in memory. Situation is as follows: All compiler versions tested return it in memory - as expected. gcc 11, gcc 12, g++ 12, and clang 13 pass it in a GPR - as expected. g++ 11 as well as clang++ 13 pass in an FPR For IBM Z we stick to the current GCC 12 behavior, i.e. zero-width bitfields are NOT ignored. A struct as above will be passed in a GPR. Rational behind this is that not affecting the C ABI is more important here. A patch for clang is in progress: https://reviews.llvm.org/D122388 In addition to the usual regression test I ran the compat and struct-layout-1 testsuites comparing the compiler before and after the patch. gcc/ChangeLog: PR target/102024 * config/s390/s390-protos.h (s390_function_arg_vector): Remove prototype. * config/s390/s390.cc (s390_single_field_struct_p): New function. (s390_function_arg_vector): Invoke s390_single_field_struct_p. (s390_function_arg_float): Likewise. gcc/testsuite/ChangeLog: PR target/102024 * g++.target/s390/pr102024-1.C: New test. * g++.target/s390/pr102024-2.C: New test. * g++.target/s390/pr102024-3.C: New test. * g++.target/s390/pr102024-4.C: New test. * g++.target/s390/pr102024-5.C: New test. * g++.target/s390/pr102024-6.C: New test.