mirror of
git://gcc.gnu.org/git/gcc.git
synced 2025-04-06 19:31:54 +08:00
a5bff8af0a
In C++14, an empty class deriving from an empty base is not an aggregate, while in C++17 it is. In order to implement this, GCC adds an artificial field to such classes. This artificial field has no mapping to Fundamental Data Types in the Arm PCS ABI and hence should not count towards determining whether an object can be passed using the vector registers as per section "7.1.2 Procedure Calling" in the arm PCS https://developer.arm.com/docs/ihi0042/latest?_ga=2.60211309.1506853196.1533541889-405231439.1528186050 This patch avoids counting this artificial field in aapcs_vfp_sub_candidate, and hence calculates whether such objects should be passed in vector registers in the same manner as C++14 (where the artificial field does not exist). Before this change, the test below would pass the arguments to `f` in general registers. After this change, the test passes the arguments to `f` using the vector registers. The new behaviour matches the behaviour of `armclang`, and also matches the GCC behaviour when run with `-std=gnu++14`. > gcc -std=gnu++17 -march=armv8-a+simd -mfloat-abi=hard test.cpp ``` test.cpp struct base {}; struct pair : base { float first; float second; pair (float f, float s) : first(f), second(s) {} }; void f (pair); int main() { f({3.14, 666}); return 1; } ``` We add a `-Wpsabi` warning to catch cases where this fix has changed the ABI for some functions. Unfortunately this warning is not emitted twice for multiple calls to the same function, but I feel this is not much of a problem and can be fixed later if needs be. (i.e. if `main` called `f` twice in a row we only emit a diagnostic for the first). Testing: Bootstrapped and regression tested on arm-linux. This change fixes the struct-layout-1 tests Jakub added https://gcc.gnu.org/pipermail/gcc-patches/2020-April/544204.html Regression tested on arm-none-eabi. gcc/ChangeLog: 2020-04-28 Matthew Malcomson <matthew.malcomson@arm.com> Jakub Jelinek <jakub@redhat.com> PR target/94711 * config/arm/arm.c (aapcs_vfp_sub_candidate): Account for C++17 empty base class artificial fields. (aapcs_vfp_is_call_or_return_candidate): Warn when PCS ABI decision is different after this fix.
This directory contains the GNU Compiler Collection (GCC). The GNU Compiler Collection is free software. See the files whose names start with COPYING for copying permission. The manuals, and some of the runtime libraries, are under different terms; see the individual source files for details. The directory INSTALL contains copies of the installation information as HTML and plain text. The source of this information is gcc/doc/install.texi. The installation information includes details of what is included in the GCC sources and what files GCC installs. See the file gcc/doc/gcc.texi (together with other files that it includes) for usage and porting information. An online readable version of the manual is in the files gcc/doc/gcc.info*. See http://gcc.gnu.org/bugs/ for how to report bugs usefully. Copyright years on GCC source files may be listed using range notation, e.g., 1987-2012, indicating that every year in the range, inclusive, is a copyrightable year that could otherwise be listed individually.