[Bug target/49001] GCC uses VMOVAPS/PD AVX instructions to access stack variables that are not 32-byte aligned

[Bug target/49001] GCC uses VMOVAPS/PD AVX instructions to access stack variables that are not 32-byte aligned

[npozar at quick dot cz]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49001

Norbert Pozar <npozar at quick dot cz> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Severity|major                       |critical

[Bug target/49001] New: GCC uses VMOVAPS/PD AVX instructions to access stack variables that are not 32-byte aligned

[npozar at quick dot cz]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49001

           Summary: GCC uses VMOVAPS/PD AVX instructions to access stack
                    variables that are not 32-byte aligned
           Product: gcc
           Version: 4.6.1
            Status: UNCONFIRMED
          Severity: major
          Priority: P3
         Component: target
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: npozar@quick.cz


I'm using a custom mingw64 build of GCC 4.6.1. My target is Windows 64bit. I
compile with g++ -03 -march=corei7-avx -mtune=corei7-avx -mavx.

GCC uses aligned moves VMOVAPS/PD from the new AVX instruction set to access
local variables of type __m256/__m256d on the stack. But the stack pointer is
only 16byte aligned on Win64, so this causes a segmentation fault error when
the stack pointer is not 32byte aligned, as in:

__m256 dummy_ps256;
void test_stackalign32() {
    __m256 x = dummy_ps256;
    dummy_ps256 = sin256_ps_avx(x);
}

which compiles to 

    vmovaps    dummy_ps256(%rip), %ymm0
    leaq    32(%rsp), %rdx
    vmovaps    %ymm0, 32(%rsp)  // possible SEGFAULT
    leaq    64(%rsp), %rcx
    vzeroupper
    call    _Z13sin256_ps_avxDv8_f
    vmovaps    64(%rsp), %ymm0  // possible SEGFAULT

I couldn't figure out how to realign a stack with -mstackrealign.

[Bug target/49001] GCC uses VMOVAPS/PD AVX instructions to access stack variables that are not 32-byte aligned

[ubizjak at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49001

Uros Bizjak <ubizjak at gmail dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |ktietz at gcc dot gnu.org
           Severity|critical                    |normal

--- Comment #1 from Uros Bizjak <ubizjak at gmail dot com> 2011-05-15 18:49:44 UTC ---
(In reply to comment #0)
> I'm using a custom mingw64 build of GCC 4.6.1. My target is Windows 64bit. I
> compile with g++ -03 -march=corei7-avx -mtune=corei7-avx -mavx.

Please provide testcase that can be compiled without changes. See [1].

FWIW, I have tested following testcase on x86_64-pc-linux-gnu:

--cut here--
#include <x86intrin.h>

__m256 sin256_ps_avx (__m256);

__m256 dummy_ps256;
void test_stackalign32() {
    volatile __m256 x = dummy_ps256;
    dummy_ps256 = sin256_ps_avx(x);
}
--cut here--

And got expected code (gcc-4.6.1):

test_stackalign32:
.LFB828:
    .cfi_startproc
    pushq    %rbp
    .cfi_def_cfa_offset 16
    .cfi_offset 6, -16
    movq    %rsp, %rbp
    .cfi_def_cfa_register 6
    andq    $-32, %rsp
    subq    $32, %rsp
    vmovaps    dummy_ps256(%rip), %ymm0
    vmovaps    %ymm0, (%rsp)
    vmovaps    (%rsp), %ymm0
    call    sin256_ps_avx
    vmovaps    %ymm0, dummy_ps256(%rip)
    leave
    .cfi_def_cfa 7, 8
    vzeroupper
    ret

Probably mingw64 specific problem... CC added.

[1] http://gcc.gnu.org/bugs/#report

[Bug target/49001] GCC uses VMOVAPS/PD AVX instructions to access stack variables that are not 32-byte aligned

[hjl.tools at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49001

--- Comment #2 from H.J. Lu <hjl.tools at gmail dot com> 2011-05-15 22:10:00 UTC ---
Stack alignment isn't supported on Windows.

[Bug target/49001] GCC uses VMOVAPS/PD AVX instructions to access stack variables that are not 32-byte aligned

[npozar at quick dot cz]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49001

--- Comment #3 from Norbert Pozar <npozar at quick dot cz> 2011-05-16 06:05:37 UTC ---
(In reply to comment #1)
> Please provide testcase that can be compiled without changes. See [1].

I'm sorry about this.

> Probably mingw64 specific problem... CC added.

Thank you for your time to test the code on linux. I was worried that this
might be mingw64 specific.

(In reply to comment #2)
> Stack alignment isn't supported on Windows.

Since this bug effectively prevents using 256bit AVX instructions when
compiling for Windows using GCC, I was wondering if there are any plans to
support the stack alignment. It seems that simply adding 

andq    $-32, %rsp

to the function prologue would fix this. Or would it be feasible to replace
VMOVAPS by unaligned VMOVUPS when accessing the stack?

[Bug target/49001] GCC uses VMOVAPS/PD AVX instructions to access stack variables that are not 32-byte aligned

[roland at rschulz dot eu]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=49001

--- Comment #4 from Roland Schulz <roland at rschulz dot eu> ---
*** Bug 61730 has been marked as a duplicate of this bug. ***

[Bug target/49001] GCC uses VMOVAPS/PD AVX instructions to access stack variables that are not 32-byte aligned

[arthur200126 at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=49001

Mingye Wang <arthur200126 at gmail dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |arthur200126 at gmail dot com

--- Comment #5 from Mingye Wang <arthur200126 at gmail dot com> ---
I think I am bumping into the same bug with GCC 10.3.0, MinGW64 environment, in
an SIMD library at [1].
  [1]: https://github.com/google/highway/issues/332

There was a related bug at [2] showing another small (not quite minimal) test
case.
  [2]: https://osdn.net/projects/mingw/ticket/39565

The VMOVUPS idea seems cool -- can we do it?

[Bug target/49001] GCC uses VMOVAPS/PD AVX instructions to access stack variables that are not 32-byte aligned

[arthur200126 at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=49001

--- Comment #6 from Mingye Wang <arthur200126 at gmail dot com> ---
FWIW, the ticket about doing stuff to align the stack in the prologue is bug
54412. Apologies for the noisy emails, but thing is I can't do the see-also
thing here.

[Bug target/49001] GCC uses VMOVAPS/PD AVX instructions to access stack variables that are not 32-byte aligned

[thiago at kde dot org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=49001

--- Comment #7 from Thiago Macieira <thiago at kde dot org> ---
Hack to workaround:

asm(
    ".macro vmovapd args:vararg\n"
    "    vmovupd \\args\n"
    ".endm\n"
    ".macro vmovaps args:vararg\n"
    "    vmovups \\args\n"
    ".endm\n"
    ".macro vmovdqa args:vararg\n"
    "    vmovdqu \\args\n"
    ".endm\n"
    ".macro vmovdqa32 args:vararg\n"
    "    vmovdqu32 \\args\n"
    ".endm\n"
    ".macro vmovdqa64 args:vararg\n"
    "    vmovdqu64 \\args\n"
    ".endm\n"
);

See:
https://github.com/opendcdiag/opendcdiag/blob/main/framework/sysdeps/windows/win32_stdlib.h#L11-L34

[Bug target/49001] GCC uses VMOVAPS/PD AVX instructions to access stack variables that are not 32-byte aligned

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=49001

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |xjkp2283572185 at gmail dot com

--- Comment #8 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
*** Bug 113989 has been marked as a duplicate of this bug. ***