development strategy for support beyond host platform

[BurntSushi]

I would like it to be possible for programmers to run tests using intrinsics that their development platform doesn't have access to. For example, as someone developing on an Intel SandyBridge machine, I'd like to be able to run tests that use AVX512 intrinsics or even ARM tests.

Is this possible? Can some kind of VM make this happen?

@mattico noted some thoughts on the topic.

[AdamNiederer]

AFAIK QEMU can't emulate AVX-512 in software, but Intel has a proprietary (I know, eww) solution to do it: https://software.intel.com/en-us/articles/intel-software-development-emulator/

I'll report on whether it can handle NEON as soon as my aarch64 toolchain builds.

EDIT: Looks like QEMU emulates NEON, although I didn't write anything exhaustive.

#include "stdio.h"

#ifdef __x86_64__
#include "x86intrin.h"
#endif

#ifdef __aarch64__
#include "arm_neon.h"
#endif

int main(void) {
#ifdef __x86_64__
  __m512d arr = _mm512_set_pd(0.0, 0.1, 0.0, 0.1, 0.0, 0.1, 0.0, 0.1);
  __m512d arr2 = _mm512_set_pd(0.0, 0.1, 0.0, 0.1, 0.0, 0.1, 0.0, 0.1);
  __m512d ans = _mm512_add_pd(arr, arr2);
  printf("%f\n", ans[0]);
#endif

#ifdef __aarch64__
  float64x2_t arr = {0.0, 1.0};
  float64x2_t arr2 = {0.0, 1.0};
  float64x2_t ans = vaddq_f64(arr, arr2);
  printf("%f, %f\n", ans[0], ans[1]);
#endif
}

$ clang -march=skylake-avx512 simd.c
$ qemu-x86_64 -cpu Skylake-Server ./a.out 
warning: TCG doesn't support requested feature: CPUID.01H:ECX.fma [bit 12]
warning: TCG doesn't support requested feature: CPUID.01H:ECX.pcid [bit 17]
warning: TCG doesn't support requested feature: CPUID.01H:ECX.x2apic [bit 21]
warning: TCG doesn't support requested feature: CPUID.01H:ECX.tsc-deadline [bit 24]
warning: TCG doesn't support requested feature: CPUID.01H:ECX.avx [bit 28]
warning: TCG doesn't support requested feature: CPUID.01H:ECX.f16c [bit 29]
warning: TCG doesn't support requested feature: CPUID.01H:ECX.rdrand [bit 30]
warning: TCG doesn't support requested feature: CPUID.07H:EBX.hle [bit 4]
warning: TCG doesn't support requested feature: CPUID.07H:EBX.avx2 [bit 5]
warning: TCG doesn't support requested feature: CPUID.07H:EBX.invpcid [bit 10]
warning: TCG doesn't support requested feature: CPUID.07H:EBX.rtm [bit 11]
warning: TCG doesn't support requested feature: CPUID.07H:EBX.avx512f [bit 16]
warning: TCG doesn't support requested feature: CPUID.07H:EBX.avx512dq [bit 17]
warning: TCG doesn't support requested feature: CPUID.07H:EBX.rdseed [bit 18]
warning: TCG doesn't support requested feature: CPUID.07H:EBX.avx512cd [bit 28]
warning: TCG doesn't support requested feature: CPUID.07H:EBX.avx512bw [bit 30]
warning: TCG doesn't support requested feature: CPUID.07H:EBX.avx512vl [bit 31]
warning: TCG doesn't support requested feature: CPUID.80000001H:ECX.3dnowprefetch [bit 8]
warning: TCG doesn't support requested feature: CPUID.0DH:EAX.xsavec [bit 1]
qemu: uncaught target signal 4 (Illegal instruction) - core dumped
Illegal instruction (core dumped)

$ aarch64-linux-gnu-gcc simd.c
$ qemu-aarch64 -L /usr/aarch64-linux-gnu/ ./a.out 
0.000000, 2.000000
$ aarch64-linux-gnu-objdump -S ./a.out | grep fadd
  4005a4:	4e60d420 	fadd	v0.2d, v1.2d, v0.2d```

This was all done on an Ivy Bridge box (AVX and below natively supported)

[alexcrichton]

Bah I would have hoped we could just use QEMU for this, but apparently not :(

[gnzlbg]

@AdamNiederer

AFAIK QEMU can't emulate AVX-512 in software,

Does anybody know if this is going to stay this way, or if it is something being worked on?

EDIT: This QEMU change log from 2016 says that it has some support for AVX-512: https://wiki.qemu.org/ChangeLog/2.8

[Rtoax]

Thanks, qemu tcg 8.2.2 still not support avx512 yet:

$ qemu-x86_64 -cpu Skylake-Server ./vfmadd231ps
qemu-x86_64: warning: TCG doesn't support requested feature: CPUID.07H:EBX.hle [bit 4]
qemu-x86_64: warning: TCG doesn't support requested feature: CPUID.07H:EBX.rtm [bit 11]
qemu-x86_64: warning: TCG doesn't support requested feature: CPUID.07H:EBX.avx512f [bit 16]
qemu-x86_64: warning: TCG doesn't support requested feature: CPUID.07H:EBX.avx512dq [bit 17]
qemu-x86_64: warning: TCG doesn't support requested feature: CPUID.07H:EBX.avx512cd [bit 28]
qemu-x86_64: warning: TCG doesn't support requested feature: CPUID.07H:EBX.avx512bw [bit 30]
qemu-x86_64: warning: TCG doesn't support requested feature: CPUID.07H:EBX.avx512vl [bit 31]
qemu-x86_64: warning: TCG doesn't support requested feature: CPUID.0DH:EAX.xsavec [bit 1]
Illegal instruction (core dumped)

[dElogics]

Confirmed with 9.1.2
qemu-x86_64 -cpu Icelake-Server-v7 bash
qemu-x86_64: warning: TCG doesn't support requested feature: CPUID.07H:EBX.hle [bit 4]
qemu-x86_64: warning: TCG doesn't support requested feature: CPUID.07H:EBX.rtm [bit 11]
qemu-x86_64: warning: TCG doesn't support requested feature: CPUID.07H:EBX.avx512f [bit 16]
qemu-x86_64: warning: TCG doesn't support requested feature: CPUID.07H:EBX.avx512dq [bit 17]
qemu-x86_64: warning: TCG doesn't support requested feature: CPUID.07H:EBX.avx512ifma [bit 21]
qemu-x86_64: warning: TCG doesn't support requested feature: CPUID.07H:EBX.avx512cd [bit 28]
qemu-x86_64: warning: TCG doesn't support requested feature: CPUID.07H:EBX.avx512bw [bit 30]
qemu-x86_64: warning: TCG doesn't support requested feature: CPUID.07H:EBX.avx512vl [bit 31]
qemu-x86_64: warning: TCG doesn't support requested feature: CPUID.07H:ECX.avx512vbmi [bit 1]
qemu-x86_64: warning: TCG doesn't support requested feature: CPUID.07H:ECX.avx512vbmi2 [bit 6]
qemu-x86_64: warning: TCG doesn't support requested feature: CPUID.07H:ECX.gfni [bit 8]
qemu-x86_64: warning: TCG doesn't support requested feature: CPUID.07H:ECX.vpclmulqdq [bit 10]
qemu-x86_64: warning: TCG doesn't support requested feature: CPUID.07H:ECX.avx512vnni [bit 11]
qemu-x86_64: warning: TCG doesn't support requested feature: CPUID.07H:ECX.avx512bitalg [bit 12]
qemu-x86_64: warning: TCG doesn't support requested feature: CPUID.07H:ECX.avx512-vpopcntdq [bit 14]