使用 ASM 发出屏蔽 vmovapd (AVX-512) 指令的正确方法是什么？
What is the right way to emit masked vmovapd (AVX-512) instructions using ASM?
我一直在尝试编写一些 AVX512 代码来转置一个 8x8 的双精度矩阵，它已经在 8 个 zmm 寄存器中。
我尝试的技巧之一是用 1 次随机播放和 2 次 mask_movs 替换 2 次随机播放，这样端口 5 的压力就更小了 - https://gcc.godbolt.org/z/HxZThj。示例代码加载并存储矩阵，但对于我的实际用例，我在 zmm 寄存器中有矩阵，需要转置保留在 zmm 寄存器中。
然而，Clang 决定只输出 3 次随机播放！
void Transpose(double* in, double* out) {
__m512d __t0, __t1, __t2, __t3, __t4, __t5, __t6, __t7;
__m512d __tt0, __tt1, __tt2, __tt3, __tt4, __tt5, __tt6, __tt7;
__m512d row0 = _mm512_load_pd(in + 0 * 8); // 0 1 2 3 4 5 6 7
__m512d row1 = _mm512_load_pd(in + 1 * 8); // 8 9 10 11 12 13 14 15
__m512d row2 = _mm512_load_pd(in + 2 * 8); // 16 17 18 19 20 21 22 23
__m512d row3 = _mm512_load_pd(in + 3 * 8); // 24 25 26 27 28 29 30 31
__m512d row4 = _mm512_load_pd(in + 4 * 8); // 32 33 34 35 36 37 38 39
__m512d row5 = _mm512_load_pd(in + 5 * 8); // 40 41 42 43 44 45 46 47
__m512d row6 = _mm512_load_pd(in + 6 * 8); // 48 49 50 51 52 53 54 55
__m512d row7 = _mm512_load_pd(in + 7 * 8); // 56 57 58 59 60 61 62 63
// IACA_START
__t0 = _mm512_unpacklo_pd(row0, row1); // 0 8 2 10 4 12 6 14
__t1 = _mm512_unpackhi_pd(row0, row1); // 1 9 3 11 5 13 7 15
__t2 = _mm512_unpacklo_pd(row2, row3); // 16 24 18 26 20 28 22 30
__t3 = _mm512_unpackhi_pd(row2, row3); // 17 25 19 27 21 29 23 31
__t4 = _mm512_unpacklo_pd(row4, row5); // 32 40 34 42 36 44 38 46
__t5 = _mm512_unpackhi_pd(row4, row5); // 33 41 35 43 37 45 39 47
__t6 = _mm512_unpacklo_pd(row6, row7); // 48 56 50 58 52 60 54 62
__t7 = _mm512_unpackhi_pd(row6, row7); // 49 57 51 59 53 61 55 63
__tt0 = _mm512_permutex2var_pd(
__t0, _mm512_setr_epi64(0, 1, 8, 9, 4, 5, 12, 13), __t2);
__tt1 = _mm512_permutex2var_pd(
__t0, _mm512_setr_epi64(2, 3, 10, 11, 6, 7, 14, 15), __t2);
__tt2 = _mm512_permutex2var_pd(
__t1, _mm512_setr_epi64(0, 1, 8, 9, 4, 5, 12, 13), __t3);
__tt3 = _mm512_permutex2var_pd(
__t1, _mm512_setr_epi64(2, 3, 10, 11, 6, 7, 14, 15), __t3);
__tt4 = _mm512_permutex2var_pd(
__t4, _mm512_setr_epi64(0, 1, 8, 9, 4, 5, 12, 13), __t6);
__tt5 = _mm512_permutex2var_pd(
__t4, _mm512_setr_epi64(2, 3, 10, 11, 6, 7, 14, 15), __t6);
__tt6 = _mm512_permutex2var_pd(
__t5, _mm512_setr_epi64(0, 1, 8, 9, 4, 5, 12, 13), __t7);
__tt7 = _mm512_permutex2var_pd(
__t5, _mm512_setr_epi64(2, 3, 10, 11, 6, 7, 14, 15), __t7);
// 0 8 16 24 4 12 20 28
// 2 10 18 26 6 14 22 30
// 1 9 17 25 5 13 21 29
// 3 11 19 27 7 15 23 31
// 32 40 48 56 36 44 52 60
// 34 42 50 58 38 46 54 62
// 33 41 49 57 37 45 53 61
// 35 43 51 59 39 47 55 63
// __t0 = _mm512_shuffle_f64x2(__tt0, __tt4, 0x44); // 0 8 16 24 32 40 48 56
// __t1 = _mm512_shuffle_f64x2(__tt2, __tt6, 0x44); // 1 9 17 25 33 41 49 57
// __t2 = _mm512_shuffle_f64x2(__tt1, __tt5, 0x44); // 2 10 18 26 34 42 50 58
// __t3 = _mm512_shuffle_f64x2(__tt3, __tt7, 0x44); // 3 11 19 27 35 43 51 59
// __t4 = _mm512_shuffle_f64x2(__tt0, __tt4, 0xee); // 4 12 20 28 36 44 52 60
// __t5 = _mm512_shuffle_f64x2(__tt2, __tt6, 0xee); // 5 13 21 29 37 45 53 61
// __t6 = _mm512_shuffle_f64x2(__tt1, __tt5, 0xee); // 6 14 22 30 38 46 54 62
// __t7 = _mm512_shuffle_f64x2(__tt3, __tt7, 0xee); // 7 15 23 31 39 47 55 63
// Tried to replace a pair of shuffles, with 1 shuffle and 2 blends.
// 2 blends should go to port 0 and be better overall.
// Clang has other ideas and does port 5 shuffles instead :(
// Can I convince Clang to do as I say some how?
{
__m512d v = _mm512_shuffle_f64x2(__tt0, __tt4, 0x4e); // 4 12 20 28 32 40 48 56
__t0 = _mm512_mask_mov_pd(__tt0, 0b11110000, v);
__t4 = _mm512_mask_mov_pd(__tt4, 0b00001111, v);
}
{
__m512d v = _mm512_shuffle_f64x2(__tt1, __tt5, 0x4e); // 6 14 22 30 34 42 50 58
__t2 = _mm512_mask_mov_pd( __tt1, 0b11110000, v); // 2 10 18 26 34 42 50 58
__t6 = _mm512_mask_mov_pd(__tt5, 0b00001111, v); // 34 42 50 58
}
{
__m512d v = _mm512_shuffle_f64x2(__tt2, __tt6, 0x4e); // 5 13 21 29 33 41 49 57
__t1 = _mm512_mask_mov_pd(__tt2, 0b11110000, v);
__t5 = _mm512_mask_mov_pd(__tt6, 0b00001111, v);
}
{
__m512d v = _mm512_shuffle_f64x2(__tt3, __tt7, 0x4e); // 7 15 23 31 35 43 51 59
__t3 = _mm512_mask_mov_pd(__tt3, 0b11110000, v);
__t7 = _mm512_mask_mov_pd(__tt7, 0b00001111, v);
}
// IACA_END
_mm512_store_pd(out + 0 * 8, __t0);
_mm512_store_pd(out + 1 * 8, __t1);
_mm512_store_pd(out + 2 * 8, __t2);
_mm512_store_pd(out + 3 * 8, __t3);
_mm512_store_pd(out + 4 * 8, __t4);
_mm512_store_pd(out + 5 * 8, __t5);
_mm512_store_pd(out + 6 * 8, __t6);
_mm512_store_pd(out + 7 * 8, __t7);
}
所以我的下一次尝试是编写一个内联汇编版本 - https://gcc.godbolt.org/z/LR6aQy。独立的 mov_stuff 函数对我来说看起来不错，但是该程序不起作用。看汇编，好像也不对。
__m512d mov_stuff(__m512d src, __mmask8 mask, __m512d a) {
asm volatile ("vmovapd %[A], %[SRC] %{%[MASK]%}\t"
: [SRC] "=v" (src) //output
: [A] "v" (a), [MASK] "Yk" (mask)); //inputs
return src;
}
// Transpose of 8x8 matrix.
// Load stores only done to generate relevant code.
// In actual code the matrix can stay completely in registers
// for multiple iterations.
// Only interested in the register ops, hence the IACA annotations there.
// Severely port 5 limited.
void Transpose(double* in, double* out) {
__m512d __t0, __t1, __t2, __t3, __t4, __t5, __t6, __t7;
__m512d __tt0, __tt1, __tt2, __tt3, __tt4, __tt5, __tt6, __tt7;
__m512d row0 = _mm512_load_pd(in + 0 * 8); // 0 1 2 3 4 5 6 7
__m512d row1 = _mm512_load_pd(in + 1 * 8); // 8 9 10 11 12 13 14 15
__m512d row2 = _mm512_load_pd(in + 2 * 8); // 16 17 18 19 20 21 22 23
__m512d row3 = _mm512_load_pd(in + 3 * 8); // 24 25 26 27 28 29 30 31
__m512d row4 = _mm512_load_pd(in + 4 * 8); // 32 33 34 35 36 37 38 39
__m512d row5 = _mm512_load_pd(in + 5 * 8); // 40 41 42 43 44 45 46 47
__m512d row6 = _mm512_load_pd(in + 6 * 8); // 48 49 50 51 52 53 54 55
__m512d row7 = _mm512_load_pd(in + 7 * 8); // 56 57 58 59 60 61 62 63
// IACA_START
__t0 = _mm512_unpacklo_pd(row0, row1); // 0 8 2 10 4 12 6 14
__t1 = _mm512_unpackhi_pd(row0, row1); // 1 9 3 11 5 13 7 15
__t2 = _mm512_unpacklo_pd(row2, row3); // 16 24 18 26 20 28 22 30
__t3 = _mm512_unpackhi_pd(row2, row3); // 17 25 19 27 21 29 23 31
__t4 = _mm512_unpacklo_pd(row4, row5); // 32 40 34 42 36 44 38 46
__t5 = _mm512_unpackhi_pd(row4, row5); // 33 41 35 43 37 45 39 47
__t6 = _mm512_unpacklo_pd(row6, row7); // 48 56 50 58 52 60 54 62
__t7 = _mm512_unpackhi_pd(row6, row7); // 49 57 51 59 53 61 55 63
__tt0 = _mm512_permutex2var_pd(
__t0, _mm512_setr_epi64(0, 1, 8, 9, 4, 5, 12, 13), __t2);
__tt1 = _mm512_permutex2var_pd(
__t0, _mm512_setr_epi64(2, 3, 10, 11, 6, 7, 14, 15), __t2);
__tt2 = _mm512_permutex2var_pd(
__t1, _mm512_setr_epi64(0, 1, 8, 9, 4, 5, 12, 13), __t3);
__tt3 = _mm512_permutex2var_pd(
__t1, _mm512_setr_epi64(2, 3, 10, 11, 6, 7, 14, 15), __t3);
__tt4 = _mm512_permutex2var_pd(
__t4, _mm512_setr_epi64(0, 1, 8, 9, 4, 5, 12, 13), __t6);
__tt5 = _mm512_permutex2var_pd(
__t4, _mm512_setr_epi64(2, 3, 10, 11, 6, 7, 14, 15), __t6);
__tt6 = _mm512_permutex2var_pd(
__t5, _mm512_setr_epi64(0, 1, 8, 9, 4, 5, 12, 13), __t7);
__tt7 = _mm512_permutex2var_pd(
__t5, _mm512_setr_epi64(2, 3, 10, 11, 6, 7, 14, 15), __t7);
// 0 8 16 24 4 12 20 28
// 2 10 18 26 6 14 22 30
// 1 9 17 25 5 13 21 29
// 3 11 19 27 7 15 23 31
// 32 40 48 56 36 44 52 60
// 34 42 50 58 38 46 54 62
// 33 41 49 57 37 45 53 61
// 35 43 51 59 39 47 55 63
// Does not work and asm looks wrong.
{
__m512d v = _mm512_shuffle_f64x2(__tt0, __tt4, 0x4e); // 4 12 20 28 32 40 48 56
__t0 = mov_stuff(__tt0, 0b11110000, v);
__t4 = mov_stuff(__tt4, 0b00001111, v);
}
{
__m512d v = _mm512_shuffle_f64x2(__tt1, __tt5, 0x4e); // 6 14 22 30 34 42 50 58
__t2 = mov_stuff( __tt1, 0b11110000, v); // 2 10 18 26 34 42 50 58
__t6 = mov_stuff(__tt5, 0b00001111, v); // 34 42 50 58
}
{
__m512d v = _mm512_shuffle_f64x2(__tt2, __tt6, 0x4e); // 5 13 21 29 33 41 49 57
__t1 = mov_stuff(__tt2, 0b11110000, v);
__t5 = mov_stuff(__tt6, 0b00001111, v);
}
{
__m512d v = _mm512_shuffle_f64x2(__tt3, __tt7, 0x4e); // 7 15 23 31 35 43 51 59
__t3 = mov_stuff(__tt3, 0b11110000, v);
__t7 = mov_stuff(__tt7, 0b00001111, v);
}
// IACA_END
_mm512_store_pd(out + 0 * 8, __t0);
_mm512_store_pd(out + 1 * 8, __t1);
_mm512_store_pd(out + 2 * 8, __t2);
_mm512_store_pd(out + 3 * 8, __t3);
_mm512_store_pd(out + 4 * 8, __t4);
_mm512_store_pd(out + 5 * 8, __t5);
_mm512_store_pd(out + 6 * 8, __t6);
_mm512_store_pd(out + 7 * 8, __t7);
}
为了找出问题，我尝试编写了一个测试程序以查看是否可以使我的汇编版本正常工作 - https://gcc.godbolt.org/z/TY7iv6。在此测试程序中，mov_stuff_non_asm() 和 mov_stuff_asm() 的独立版本看起来相同，但是当我在程序中使用它们时，asm 版本编译成在我看来像垃圾的东西。
__m512d mov_stuff_non_asm(__m512d src, __mmask8 mask, __m512d a)
{
return _mm512_mask_mov_pd(src, mask, a);
}
// Trying to emulate mov_stuff_non_asm here.
// Assembly on its own looks identical to the non-asm version.
// But in a full program it compiles to rubbish as seen in the main_asm
// program.
__m512d mov_stuff_asm(__m512d src, __mmask8 mask, __m512d a)
{
asm volatile ("vmovapd %[A], %[SRC] %{%[MASK]%}\t"
: [SRC] "=v" (src) //output
: [A] "v" (a), [MASK] "Yk" (mask)); //inputs
return src;
}
int main_asm() {
__mmask8 upper_lower = 0b11110000;
__mmask8 lower_upper = 0b00001111;
__m512d t0 = _mm512_setr_pd(0, 8, 16, 24, 4, 12, 20, 28);
__m512d t4 = _mm512_setr_pd(32, 40, 48, 56, 36, 44, 52, 60);
__m512d v = _mm512_shuffle_f64x2(t0, t4, 0x4e); // 4 12 20 28 32 40 48 56
__m512d new_t0 = mov_stuff_asm(t0, upper_lower, v);
DoStuff(new_t0);
}
int main_non_asm() {
__mmask8 upper_lower = 0b11110000;
__mmask8 lower_upper = 0b00001111;
__m512d t0 = _mm512_setr_pd(0, 8, 16, 24, 4, 12, 20, 28);
__m512d t4 = _mm512_setr_pd(32, 40, 48, 56, 36, 44, 52, 60);
__m512d v = _mm512_shuffle_f64x2(t0, t4, 0x4e); // 4 12 20 28 32 40 48 56
__m512d new_t0 = mov_stuff_non_asm(t0, upper_lower, v);
DoStuff(new_t0);
}
我做错了什么？是否有任何关于如何使用内联汇编编写屏蔽 AVX-512 操作的好文档。或者，如果我可以用其他方式哄 Clang 做我真正想让它做的事？
把我的评论变成答案，因为它似乎已经解决了问题。
查看您的 asm，您正在使用约束 [SRC] "=v" (src)。 '=' 在这种情况下 indicates 表示此变量将在退出 asm 时分配 SRC 的值，但输入值将被忽略（即 output-only 变量）。由于输入值被忽略，clang 的优化器可以丢弃在此之前计算该值的任何代码（因为您已经告诉它它不会被使用）。
将“=”更改为“+”表示 SRC 中的现有值是 更新的 而不是输出，我相信这正是您在这里的意图。
我一直在尝试编写一些 AVX512 代码来转置一个 8x8 的双精度矩阵，它已经在 8 个 zmm 寄存器中。
我尝试的技巧之一是用 1 次随机播放和 2 次 mask_movs 替换 2 次随机播放，这样端口 5 的压力就更小了 - https://gcc.godbolt.org/z/HxZThj。示例代码加载并存储矩阵，但对于我的实际用例，我在 zmm 寄存器中有矩阵，需要转置保留在 zmm 寄存器中。 然而，Clang 决定只输出 3 次随机播放！
void Transpose(double* in, double* out) {
__m512d __t0, __t1, __t2, __t3, __t4, __t5, __t6, __t7;
__m512d __tt0, __tt1, __tt2, __tt3, __tt4, __tt5, __tt6, __tt7;
__m512d row0 = _mm512_load_pd(in + 0 * 8); // 0 1 2 3 4 5 6 7
__m512d row1 = _mm512_load_pd(in + 1 * 8); // 8 9 10 11 12 13 14 15
__m512d row2 = _mm512_load_pd(in + 2 * 8); // 16 17 18 19 20 21 22 23
__m512d row3 = _mm512_load_pd(in + 3 * 8); // 24 25 26 27 28 29 30 31
__m512d row4 = _mm512_load_pd(in + 4 * 8); // 32 33 34 35 36 37 38 39
__m512d row5 = _mm512_load_pd(in + 5 * 8); // 40 41 42 43 44 45 46 47
__m512d row6 = _mm512_load_pd(in + 6 * 8); // 48 49 50 51 52 53 54 55
__m512d row7 = _mm512_load_pd(in + 7 * 8); // 56 57 58 59 60 61 62 63
// IACA_START
__t0 = _mm512_unpacklo_pd(row0, row1); // 0 8 2 10 4 12 6 14
__t1 = _mm512_unpackhi_pd(row0, row1); // 1 9 3 11 5 13 7 15
__t2 = _mm512_unpacklo_pd(row2, row3); // 16 24 18 26 20 28 22 30
__t3 = _mm512_unpackhi_pd(row2, row3); // 17 25 19 27 21 29 23 31
__t4 = _mm512_unpacklo_pd(row4, row5); // 32 40 34 42 36 44 38 46
__t5 = _mm512_unpackhi_pd(row4, row5); // 33 41 35 43 37 45 39 47
__t6 = _mm512_unpacklo_pd(row6, row7); // 48 56 50 58 52 60 54 62
__t7 = _mm512_unpackhi_pd(row6, row7); // 49 57 51 59 53 61 55 63
__tt0 = _mm512_permutex2var_pd(
__t0, _mm512_setr_epi64(0, 1, 8, 9, 4, 5, 12, 13), __t2);
__tt1 = _mm512_permutex2var_pd(
__t0, _mm512_setr_epi64(2, 3, 10, 11, 6, 7, 14, 15), __t2);
__tt2 = _mm512_permutex2var_pd(
__t1, _mm512_setr_epi64(0, 1, 8, 9, 4, 5, 12, 13), __t3);
__tt3 = _mm512_permutex2var_pd(
__t1, _mm512_setr_epi64(2, 3, 10, 11, 6, 7, 14, 15), __t3);
__tt4 = _mm512_permutex2var_pd(
__t4, _mm512_setr_epi64(0, 1, 8, 9, 4, 5, 12, 13), __t6);
__tt5 = _mm512_permutex2var_pd(
__t4, _mm512_setr_epi64(2, 3, 10, 11, 6, 7, 14, 15), __t6);
__tt6 = _mm512_permutex2var_pd(
__t5, _mm512_setr_epi64(0, 1, 8, 9, 4, 5, 12, 13), __t7);
__tt7 = _mm512_permutex2var_pd(
__t5, _mm512_setr_epi64(2, 3, 10, 11, 6, 7, 14, 15), __t7);
// 0 8 16 24 4 12 20 28
// 2 10 18 26 6 14 22 30
// 1 9 17 25 5 13 21 29
// 3 11 19 27 7 15 23 31
// 32 40 48 56 36 44 52 60
// 34 42 50 58 38 46 54 62
// 33 41 49 57 37 45 53 61
// 35 43 51 59 39 47 55 63
// __t0 = _mm512_shuffle_f64x2(__tt0, __tt4, 0x44); // 0 8 16 24 32 40 48 56
// __t1 = _mm512_shuffle_f64x2(__tt2, __tt6, 0x44); // 1 9 17 25 33 41 49 57
// __t2 = _mm512_shuffle_f64x2(__tt1, __tt5, 0x44); // 2 10 18 26 34 42 50 58
// __t3 = _mm512_shuffle_f64x2(__tt3, __tt7, 0x44); // 3 11 19 27 35 43 51 59
// __t4 = _mm512_shuffle_f64x2(__tt0, __tt4, 0xee); // 4 12 20 28 36 44 52 60
// __t5 = _mm512_shuffle_f64x2(__tt2, __tt6, 0xee); // 5 13 21 29 37 45 53 61
// __t6 = _mm512_shuffle_f64x2(__tt1, __tt5, 0xee); // 6 14 22 30 38 46 54 62
// __t7 = _mm512_shuffle_f64x2(__tt3, __tt7, 0xee); // 7 15 23 31 39 47 55 63
// Tried to replace a pair of shuffles, with 1 shuffle and 2 blends.
// 2 blends should go to port 0 and be better overall.
// Clang has other ideas and does port 5 shuffles instead :(
// Can I convince Clang to do as I say some how?
{
__m512d v = _mm512_shuffle_f64x2(__tt0, __tt4, 0x4e); // 4 12 20 28 32 40 48 56
__t0 = _mm512_mask_mov_pd(__tt0, 0b11110000, v);
__t4 = _mm512_mask_mov_pd(__tt4, 0b00001111, v);
}
{
__m512d v = _mm512_shuffle_f64x2(__tt1, __tt5, 0x4e); // 6 14 22 30 34 42 50 58
__t2 = _mm512_mask_mov_pd( __tt1, 0b11110000, v); // 2 10 18 26 34 42 50 58
__t6 = _mm512_mask_mov_pd(__tt5, 0b00001111, v); // 34 42 50 58
}
{
__m512d v = _mm512_shuffle_f64x2(__tt2, __tt6, 0x4e); // 5 13 21 29 33 41 49 57
__t1 = _mm512_mask_mov_pd(__tt2, 0b11110000, v);
__t5 = _mm512_mask_mov_pd(__tt6, 0b00001111, v);
}
{
__m512d v = _mm512_shuffle_f64x2(__tt3, __tt7, 0x4e); // 7 15 23 31 35 43 51 59
__t3 = _mm512_mask_mov_pd(__tt3, 0b11110000, v);
__t7 = _mm512_mask_mov_pd(__tt7, 0b00001111, v);
}
// IACA_END
_mm512_store_pd(out + 0 * 8, __t0);
_mm512_store_pd(out + 1 * 8, __t1);
_mm512_store_pd(out + 2 * 8, __t2);
_mm512_store_pd(out + 3 * 8, __t3);
_mm512_store_pd(out + 4 * 8, __t4);
_mm512_store_pd(out + 5 * 8, __t5);
_mm512_store_pd(out + 6 * 8, __t6);
_mm512_store_pd(out + 7 * 8, __t7);
}
所以我的下一次尝试是编写一个内联汇编版本 - https://gcc.godbolt.org/z/LR6aQy。独立的 mov_stuff 函数对我来说看起来不错，但是该程序不起作用。看汇编，好像也不对。
__m512d mov_stuff(__m512d src, __mmask8 mask, __m512d a) {
asm volatile ("vmovapd %[A], %[SRC] %{%[MASK]%}\t"
: [SRC] "=v" (src) //output
: [A] "v" (a), [MASK] "Yk" (mask)); //inputs
return src;
}
// Transpose of 8x8 matrix.
// Load stores only done to generate relevant code.
// In actual code the matrix can stay completely in registers
// for multiple iterations.
// Only interested in the register ops, hence the IACA annotations there.
// Severely port 5 limited.
void Transpose(double* in, double* out) {
__m512d __t0, __t1, __t2, __t3, __t4, __t5, __t6, __t7;
__m512d __tt0, __tt1, __tt2, __tt3, __tt4, __tt5, __tt6, __tt7;
__m512d row0 = _mm512_load_pd(in + 0 * 8); // 0 1 2 3 4 5 6 7
__m512d row1 = _mm512_load_pd(in + 1 * 8); // 8 9 10 11 12 13 14 15
__m512d row2 = _mm512_load_pd(in + 2 * 8); // 16 17 18 19 20 21 22 23
__m512d row3 = _mm512_load_pd(in + 3 * 8); // 24 25 26 27 28 29 30 31
__m512d row4 = _mm512_load_pd(in + 4 * 8); // 32 33 34 35 36 37 38 39
__m512d row5 = _mm512_load_pd(in + 5 * 8); // 40 41 42 43 44 45 46 47
__m512d row6 = _mm512_load_pd(in + 6 * 8); // 48 49 50 51 52 53 54 55
__m512d row7 = _mm512_load_pd(in + 7 * 8); // 56 57 58 59 60 61 62 63
// IACA_START
__t0 = _mm512_unpacklo_pd(row0, row1); // 0 8 2 10 4 12 6 14
__t1 = _mm512_unpackhi_pd(row0, row1); // 1 9 3 11 5 13 7 15
__t2 = _mm512_unpacklo_pd(row2, row3); // 16 24 18 26 20 28 22 30
__t3 = _mm512_unpackhi_pd(row2, row3); // 17 25 19 27 21 29 23 31
__t4 = _mm512_unpacklo_pd(row4, row5); // 32 40 34 42 36 44 38 46
__t5 = _mm512_unpackhi_pd(row4, row5); // 33 41 35 43 37 45 39 47
__t6 = _mm512_unpacklo_pd(row6, row7); // 48 56 50 58 52 60 54 62
__t7 = _mm512_unpackhi_pd(row6, row7); // 49 57 51 59 53 61 55 63
__tt0 = _mm512_permutex2var_pd(
__t0, _mm512_setr_epi64(0, 1, 8, 9, 4, 5, 12, 13), __t2);
__tt1 = _mm512_permutex2var_pd(
__t0, _mm512_setr_epi64(2, 3, 10, 11, 6, 7, 14, 15), __t2);
__tt2 = _mm512_permutex2var_pd(
__t1, _mm512_setr_epi64(0, 1, 8, 9, 4, 5, 12, 13), __t3);
__tt3 = _mm512_permutex2var_pd(
__t1, _mm512_setr_epi64(2, 3, 10, 11, 6, 7, 14, 15), __t3);
__tt4 = _mm512_permutex2var_pd(
__t4, _mm512_setr_epi64(0, 1, 8, 9, 4, 5, 12, 13), __t6);
__tt5 = _mm512_permutex2var_pd(
__t4, _mm512_setr_epi64(2, 3, 10, 11, 6, 7, 14, 15), __t6);
__tt6 = _mm512_permutex2var_pd(
__t5, _mm512_setr_epi64(0, 1, 8, 9, 4, 5, 12, 13), __t7);
__tt7 = _mm512_permutex2var_pd(
__t5, _mm512_setr_epi64(2, 3, 10, 11, 6, 7, 14, 15), __t7);
// 0 8 16 24 4 12 20 28
// 2 10 18 26 6 14 22 30
// 1 9 17 25 5 13 21 29
// 3 11 19 27 7 15 23 31
// 32 40 48 56 36 44 52 60
// 34 42 50 58 38 46 54 62
// 33 41 49 57 37 45 53 61
// 35 43 51 59 39 47 55 63
// Does not work and asm looks wrong.
{
__m512d v = _mm512_shuffle_f64x2(__tt0, __tt4, 0x4e); // 4 12 20 28 32 40 48 56
__t0 = mov_stuff(__tt0, 0b11110000, v);
__t4 = mov_stuff(__tt4, 0b00001111, v);
}
{
__m512d v = _mm512_shuffle_f64x2(__tt1, __tt5, 0x4e); // 6 14 22 30 34 42 50 58
__t2 = mov_stuff( __tt1, 0b11110000, v); // 2 10 18 26 34 42 50 58
__t6 = mov_stuff(__tt5, 0b00001111, v); // 34 42 50 58
}
{
__m512d v = _mm512_shuffle_f64x2(__tt2, __tt6, 0x4e); // 5 13 21 29 33 41 49 57
__t1 = mov_stuff(__tt2, 0b11110000, v);
__t5 = mov_stuff(__tt6, 0b00001111, v);
}
{
__m512d v = _mm512_shuffle_f64x2(__tt3, __tt7, 0x4e); // 7 15 23 31 35 43 51 59
__t3 = mov_stuff(__tt3, 0b11110000, v);
__t7 = mov_stuff(__tt7, 0b00001111, v);
}
// IACA_END
_mm512_store_pd(out + 0 * 8, __t0);
_mm512_store_pd(out + 1 * 8, __t1);
_mm512_store_pd(out + 2 * 8, __t2);
_mm512_store_pd(out + 3 * 8, __t3);
_mm512_store_pd(out + 4 * 8, __t4);
_mm512_store_pd(out + 5 * 8, __t5);
_mm512_store_pd(out + 6 * 8, __t6);
_mm512_store_pd(out + 7 * 8, __t7);
}
为了找出问题，我尝试编写了一个测试程序以查看是否可以使我的汇编版本正常工作 - https://gcc.godbolt.org/z/TY7iv6。在此测试程序中，mov_stuff_non_asm() 和 mov_stuff_asm() 的独立版本看起来相同，但是当我在程序中使用它们时，asm 版本编译成在我看来像垃圾的东西。
__m512d mov_stuff_non_asm(__m512d src, __mmask8 mask, __m512d a)
{
return _mm512_mask_mov_pd(src, mask, a);
}
// Trying to emulate mov_stuff_non_asm here.
// Assembly on its own looks identical to the non-asm version.
// But in a full program it compiles to rubbish as seen in the main_asm
// program.
__m512d mov_stuff_asm(__m512d src, __mmask8 mask, __m512d a)
{
asm volatile ("vmovapd %[A], %[SRC] %{%[MASK]%}\t"
: [SRC] "=v" (src) //output
: [A] "v" (a), [MASK] "Yk" (mask)); //inputs
return src;
}
int main_asm() {
__mmask8 upper_lower = 0b11110000;
__mmask8 lower_upper = 0b00001111;
__m512d t0 = _mm512_setr_pd(0, 8, 16, 24, 4, 12, 20, 28);
__m512d t4 = _mm512_setr_pd(32, 40, 48, 56, 36, 44, 52, 60);
__m512d v = _mm512_shuffle_f64x2(t0, t4, 0x4e); // 4 12 20 28 32 40 48 56
__m512d new_t0 = mov_stuff_asm(t0, upper_lower, v);
DoStuff(new_t0);
}
int main_non_asm() {
__mmask8 upper_lower = 0b11110000;
__mmask8 lower_upper = 0b00001111;
__m512d t0 = _mm512_setr_pd(0, 8, 16, 24, 4, 12, 20, 28);
__m512d t4 = _mm512_setr_pd(32, 40, 48, 56, 36, 44, 52, 60);
__m512d v = _mm512_shuffle_f64x2(t0, t4, 0x4e); // 4 12 20 28 32 40 48 56
__m512d new_t0 = mov_stuff_non_asm(t0, upper_lower, v);
DoStuff(new_t0);
}
我做错了什么？是否有任何关于如何使用内联汇编编写屏蔽 AVX-512 操作的好文档。或者，如果我可以用其他方式哄 Clang 做我真正想让它做的事？
把我的评论变成答案，因为它似乎已经解决了问题。
查看您的 asm，您正在使用约束 [SRC] "=v" (src)。 '=' 在这种情况下 indicates 表示此变量将在退出 asm 时分配 SRC 的值，但输入值将被忽略（即 output-only 变量）。由于输入值被忽略，clang 的优化器可以丢弃在此之前计算该值的任何代码（因为您已经告诉它它不会被使用）。
将“=”更改为“+”表示 SRC 中的现有值是 更新的 而不是输出，我相信这正是您在这里的意图。