gcc: Patch misaligned AVX spills (GCC bug 54412)

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=54412

README.md

@@ -183,10 +183,6 @@ ported to Mingw-w64][san] ([also][san2]), but Undefined Behavior Sanitizer
 `-fsanitize-trap`, GDB will [break precisely][break] on undefined
 behavior, and it does not require linking with libsanitizer.
 
-[GCC does not fully support AVX on Windows][avx] and may use aligned moves
-on unaligned addresses. When targeting AVX, consider disabling all aligned
-moves in the assembler: `-Wa,-muse-unaligned-vector-move`.
-
 ## Licenses
 
 When distributing binaries built using w64devkit, your .exe will include
@@ -201,7 +197,6 @@ w64devkit includes the concatenated set of all licenses in the file
 binaries.
 
 
-[avx]: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=54412
 [bb]: https://frippery.org/busybox/
 [break]: https://nullprogram.com/blog/2022/06/26/
 [bs]: https://www.rdegges.com/2016/i-dont-give-a-shit-about-licensing/

src/gcc-avx-misaligned.patch

@@ -0,0 +1,16 @@
+Treat AVX register spills as always unaligned, eliminating the
+requirement for -Wa,-muse-unaligned-vector-move when targeting
+AVX-capable hardware.
+
+https://gcc.gnu.org/bugzilla/show_bug.cgi?id=54412
+
+--- a/gcc/config/i386/predicates.md
++++ b/gcc/config/i386/predicates.md
+@@ -1695,5 +1695,6 @@
+ (define_predicate "misaligned_operand"
+   (and (match_code "mem")
+-       (match_test "MEM_ALIGN (op) < GET_MODE_BITSIZE (mode)")))
++       (ior (match_test "MEM_SIZE (op) > 16")
++            (match_test "MEM_ALIGN (op) < GET_MODE_BITSIZE (mode)"))))
+ 
+ ;; Return true if OP is a parallel for an mov{d,q,dqa,ps,pd} vec_select,