https://gcc.gnu.org/bugzilla/show_bug.cgi?id=54412
Dmitry Kazakov <dimula73 at gmail dot com> changed:
What |Removed |Added
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CC| |dimula73 at gmail dot com
--- Comment #25 from Dmitry Kazakov <dimula73 at gmail dot com> ---
Hi, all!
I would like to add one more test file, related to the problem. If GCC tries to
call a function, that accepts a __m256 register as a parameter, it unloads this
parameter into the stack using an **aligned** move (vmovaps), but the alignment
guarantee on Windows is only 16-byte. It means that the application will crash
because of unaligned memory access.
Affected versions: GCC 7.3.0 (MinGW64), GCC 8.1.0 (MinGW64)
Here is the testing source (see also in an attachment):
#include <intrin.h>
struct X {
alignas(32) __m256 d;
};
void g1(X);
void g2(const X&);
void g3(const void *);
void f(float *ptr) {
X x = {_mm256_load_ps(ptr)};
g1(x); // BUG: passes via unaligned (whatever rsp alignment is) stack
g2(x); // OK: passes via aligned stack location
g3(&x); // OK: passes via aligned stack location
}
Compiled result (-O2 -march=skylake):
_Z1fPf:
.LFB5135:
pushq %rbx
.seh_pushreg %rbx
addq $-128, %rsp
.seh_stackalloc 128
.seh_endprologue
vmovaps (%rcx), %ymm0
leaq 95(%rsp), %rbx
leaq 32(%rsp), %rcx
andq $-32, %rbx
vmovaps %ymm0, (%rbx) # %rbx is properly aligned
vmovaps %ymm0, 32(%rsp) # %rsp may be unaligned
vzeroupper
call _Z2g11X
movq %rbx, %rcx
call _Z2g2RK1X
movq %rbx, %rcx
call _Z2g3PKv
nop
subq $-128, %rsp
popq %rbx
ret
Related bug in Vc library: https://github.com/VcDevel/Vc/issues/241
Related bug in Krita: https://bugs.kde.org/show_bug.cgi?id=406209
