[Bug target/111107] i686-w64-mingw32 does not realign stack when __attribute__((aligned)) or __attribute__((vector_size)) are used

["rguenth at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111107

Richard Biener <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
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                 CC|                            |10walls at gmail dot com

--- Comment #5 from Richard Biener <rguenth at gcc dot gnu.org> ---
I'd say that

config/i386/cygming.h:#define STACK_REALIGN_DEFAULT TARGET_SSE

is a non-working "fix".  The appropriate default would be
-mincoming-stack-boundary=2.  MIN_STACK_BOUNDARY should already be 4, so that
leaves PREFERRED_STACK_BOUNDARY_DEFAULT is the way to go here.  I also see

/* It should be MIN_STACK_BOUNDARY.  But we set it to 128 bits for
   both 32bit and 64bit, to support codes that need 128 bit stack
   alignment for SSE instructions, but can't realign the stack.  */
#define PREFERRED_STACK_BOUNDARY_DEFAULT \
  (TARGET_IAMCU ? MIN_STACK_BOUNDARY : 128)

which suggests there might be problems with SSE anyway.

So does the following work?

diff --git a/gcc/config/i386/cygming.h b/gcc/config/i386/cygming.h
index d539f8d0699..e8db548510b 100644
--- a/gcc/config/i386/cygming.h
+++ b/gcc/config/i386/cygming.h
@@ -31,10 +31,9 @@ along with GCC; see the file COPYING3.  If not see
 #undef MAX_STACK_ALIGNMENT
 #define MAX_STACK_ALIGNMENT  (TARGET_SEH ? 128 : MAX_OFILE_ALIGNMENT)

-/* 32-bit Windows aligns the stack on a 4-byte boundary but SSE instructions
-   may require 16-byte alignment.  */
-#undef STACK_REALIGN_DEFAULT
-#define STACK_REALIGN_DEFAULT TARGET_SSE
+/* 32-bit Windows aligns the stack on a 4-byte boundary.  */
+#undef PREFERRED_STACK_BOUNDARY_DEFAULT
+#define PREFERRED_STACK_BOUNDARY_DEFAULT (TARGET_64BIT ? 128 : 32)

 /* Support hooks for SEH.  */
 #undef  TARGET_ASM_UNWIND_EMIT