https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111107
--- Comment #45 from GCC Commits <cvs-commit at gcc dot gnu.org> --- The master branch has been updated by Jonathan Yong <jy...@gcc.gnu.org>: https://gcc.gnu.org/g:ee7c0a5b70dc316477f45abc0f09dd2af9abe5cb commit r16-511-gee7c0a5b70dc316477f45abc0f09dd2af9abe5cb Author: LIU Hao <lh_mo...@126.com> Date: Tue Apr 29 10:43:06 2025 +0800 i386/cygming: Decrease default preferred stack boundary for 32-bit targets This commit decreases the default preferred stack boundary to 4. In i386-options.cc, there's ix86_default_incoming_stack_boundary = PREFERRED_STACK_BOUNDARY; which sets the default incoming stack boundary to this value, if it's not overridden by other options or attributes. Previously, GCC preferred 16-byte alignment like other platforms, unless `-miamcu` was specified. However, the Microsoft x86 ABI only requires the stack be aligned to 4-byte boundaries. Callback functions from MSVC code may break this assumption by GCC (see reference below), causing local variables to be misaligned. For compatibility reasons, when the attribute `force_align_arg_pointer` is attached to a function, it continues to ensure the stack is at least aligned to a 16-byte boundary, as the documentation seems to suggest. After this change, `STACK_REALIGN_DEFAULT` no longer has an effect on this target, so it is removed. Reference: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111107#c9 Signed-off-by: LIU Hao <lh_mo...@126.com> Signed-off-by: Jonathan Yong <10wa...@gmail.com> gcc/ChangeLog: PR target/111107 * config/i386/cygming.h (PREFERRED_STACK_BOUNDARY_DEFAULT): Override definition from i386.h. (STACK_REALIGN_DEFAULT): Undefine, as it no longer has an effect. * config/i386/i386.cc (ix86_update_stack_boundary): Force minimum 128-bit alignment if `force_align_arg_pointer`.
