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      1 // Copyright 2015 Google Inc. All Rights Reserved.
      2 //
      3 // Licensed under the Apache License, Version 2.0 (the "License");
      4 // you may not use this file except in compliance with the License.
      5 // You may obtain a copy of the License at
      6 //
      7 //     http://www.apache.org/licenses/LICENSE-2.0
      8 //
      9 // Unless required by applicable law or agreed to in writing, software
     10 // distributed under the License is distributed on an "AS IS" BASIS,
     11 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
     12 // See the License for the specific language governing permissions and
     13 // limitations under the License.
     14 
     15 // kernel_neon.h: a collection of NEON optimized kernels.
     16 // Check in kernel_default.h which one(s) are actually used by default.
     17 // Others are mere experiments; they are still covered by tests
     18 // in case they might be useful some day.
     19 
     20 #ifndef GEMMLOWP_INTERNAL_KERNEL_NEON_H_
     21 #define GEMMLOWP_INTERNAL_KERNEL_NEON_H_
     22 
     23 #include "kernel.h"
     24 
     25 #include <arm_neon.h>
     26 #include <cassert>
     27 
     28 namespace gemmlowp {
     29 
     30 // The kernels here are specifically arm 32bit assembly, not arm 64bit.
     31 #ifdef GEMMLOWP_NEON_32
     32 
     33 // Our main GEMM kernel.
     34 struct NEON_32_Kernel12x4Depth2 : KernelBase {
     35   typedef KernelFormat<KernelSideFormat<CellFormat<4, 2>, 3>,
     36                        KernelSideFormat<CellFormat<4, 2>, 1> >
     37       Format;
     38 
     39   const char* Name() const override { return "NEON, 12x4, depth 2"; }
     40 
     41   // TODO(benoitjacob): reorder function arguments so dst comes last
     42   void Run(std::int32_t* dst_ptr, std::size_t dst_row_stride,
     43            std::size_t dst_col_stride, const std::uint8_t* lhs_ptr,
     44            const std::uint8_t* rhs_ptr, std::size_t start_depth,
     45            std::size_t run_depth) const override {
     46     ScopedProfilingLabel label("optimized kernel (NEON 12x4)");
     47 
     48 // For iOS assembler, the %= style of local labels cause compilation errors,
     49 //  so use numerical ones instead. See
     50 // http://stackoverflow.com/questions/3898435/labels-in-gcc-inline-assembly
     51 // If you add any labels, remember to undef them at the end.
     52 #define GEMMLOWP_LOOP_NEON_KERNEL_12X4_DEPTH2 "1"
     53 #define GEMMLOWP_STORE_RESULT_NEON_KERNEL_12X4_DEPTH2 "2"
     54 
     55     assert(dst_row_stride == 1);
     56     asm volatile(
     57         // Clear accumulator registers (see layout below)
     58         "vmov.s32 q4, #0\n"
     59         "vmov.s32 q8, q4\n"
     60         "vmov.s32 q12, q4\n"
     61         "vmov.s32 q5, q4\n"
     62         "vmov.s32 q9, q4\n"
     63         "vmov.s32 q13, q4\n"
     64         "vmov.s32 q6, q4\n"
     65         "vmov.s32 q10, q4\n"
     66         "vmov.s32 q14, q4\n"
     67         "vmov.s32 q7, q4\n"
     68         "vmov.s32 q11, q4\n"
     69         "vmov.s32 q15, q4\n"
     70 
     71         /* Main loop */
     72 
     73         GEMMLOWP_LOOP_NEON_KERNEL_12X4_DEPTH2
     74         ":\n"
     75 
     76         // Overview of register layout:
     77         //
     78         // A 2x4 cell of Rhs is stored in 16bit in d0--d1 (q0).
     79         // A 12x2 block of 3 4x2 cells Lhs is stored in 16bit in d2--d7
     80         // (q1--q3).
     81         // A 12x4 block of accumulators is stored in 32bit in q4--q15.
     82         //
     83         //                   +-----+-----+-----+-----+
     84         //                   |d0[0]|d0[1]|d0[2]|d0[3]|
     85         //              Rhs  +-----+-----+-----+-----+
     86         //                   |d1[0]|d1[1]|d1[2]|d1[3]|
     87         //                   +-----+-----+-----+-----+
     88         //
     89         //                   |     |     |     |     |
     90         //
     91         //    Lhs            |     |     |     |     |
     92         //
     93         //  +--+--+ - - - -  +-----+-----+-----+-----+
     94         //  |d2|d3|          | q4  | q5  | q6  | q7  |
     95         //  |d2|d3|          | q4  | q5  | q6  | q7  |
     96         //  |d2|d3|          | q4  | q5  | q6  | q7  |
     97         //  |d2|d3|          | q4  | q5  | q6  | q7  |
     98         //  +--+--+ - - - -  +-----+-----+-----+-----+
     99         //  |d4|d5|          | q8  | q9  | q10 | q11 |
    100         //  |d4|d5|          | q8  | q9  | q10 | q11 |
    101         //  |d4|d5|          | q8  | q9  | q10 | q11 |
    102         //  |d4|d5|          | q8  | q9  | q10 | q11 |
    103         //  +--+--+ - - - -  +-----+-----+-----+-----+
    104         //  |d6|d7|          | q12 | q13 | q14 | q15 |
    105         //  |d6|d7|          | q12 | q13 | q14 | q15 |
    106         //  |d6|d7|          | q12 | q13 | q14 | q15 |
    107         //  |d6|d7|          | q12 | q13 | q14 | q15 |
    108         //  +--+--+ - - - -  +-----+-----+-----+-----+
    109         //
    110         //                            Accumulator
    111 
    112         // Load 1 Rhs cell of size 2x4
    113         "vld1.8 {d0}, [%[rhs_ptr]:64]!\n"
    114 
    115         // Load 3 Lhs cells of size 4x2 each
    116         "vld1.8 {d2}, [%[lhs_ptr]:64]!\n"
    117         "vld1.8 {d4}, [%[lhs_ptr]:64]!\n"
    118         "vld1.8 {d6}, [%[lhs_ptr]:64]!\n"
    119 
    120         // Expand Lhs/Rhs cells to 16 bit.
    121         "vmovl.u8 q0, d0\n"
    122         "vmovl.u8 q1, d2\n"
    123         "vmovl.u8 q2, d4\n"
    124         "vmovl.u8 q3, d6\n"
    125 
    126         // Multiply-accumulate, level of depth 0
    127         "vmlal.u16 q4, d2, d0[0]\n"
    128         "vmlal.u16 q5, d2, d0[1]\n"
    129         "vmlal.u16 q6, d2, d0[2]\n"
    130         "vmlal.u16 q7, d2, d0[3]\n"
    131         "vmlal.u16 q8, d4, d0[0]\n"
    132         "vmlal.u16 q9, d4, d0[1]\n"
    133         "vmlal.u16 q10, d4, d0[2]\n"
    134         "vmlal.u16 q11, d4, d0[3]\n"
    135         "vmlal.u16 q12, d6, d0[0]\n"
    136         "vmlal.u16 q13, d6, d0[1]\n"
    137         "vmlal.u16 q14, d6, d0[2]\n"
    138         "vmlal.u16 q15, d6, d0[3]\n"
    139 
    140         // Multiply-accumulate, level of depth 1
    141         "vmlal.u16 q4, d3, d1[0]\n"
    142         "vmlal.u16 q5, d3, d1[1]\n"
    143         "vmlal.u16 q6, d3, d1[2]\n"
    144         "vmlal.u16 q7, d3, d1[3]\n"
    145         "vmlal.u16 q8, d5, d1[0]\n"
    146         "vmlal.u16 q9, d5, d1[1]\n"
    147         "vmlal.u16 q10, d5, d1[2]\n"
    148         "vmlal.u16 q11, d5, d1[3]\n"
    149         "vmlal.u16 q12, d7, d1[0]\n"
    150         "vmlal.u16 q13, d7, d1[1]\n"
    151         "vmlal.u16 q14, d7, d1[2]\n"
    152         "vmlal.u16 q15, d7, d1[3]\n"
    153 
    154         // Loop. Decrement loop index (depth) by 2, since we just handled 2
    155         // levels of depth (Kernel::kDepth=2).
    156         "subs %[run_depth], #2\n"
    157         "bne " GEMMLOWP_LOOP_NEON_KERNEL_12X4_DEPTH2
    158         "b\n"
    159 
    160         /* end of main loop */
    161 
    162         /* Accumulate our local accumulator registers into the destination block
    163            */
    164 
    165         // Compute stride between consecutive columns, in bytes
    166         "mov r0, #4\n"  // multiply by 4 = sizeof(int32)
    167         "mul %[dst_col_stride], r0\n"
    168 
    169         // If start_depth == 0, then there is no preexisting accumulator
    170         // to accumulate, so we can simply store our result.
    171         "cmp %[start_depth], #0\n"
    172         "beq " GEMMLOWP_STORE_RESULT_NEON_KERNEL_12X4_DEPTH2
    173         "f\n"
    174 
    175         "mov r0, %[dst_ptr]\n"
    176 
    177         // Load a column
    178         "mov r1, r0\n"
    179         "vld1.32 {d0, d1}, [r1]!\n"
    180         "vld1.32 {d2, d3}, [r1]!\n"
    181         "vld1.32 {d4, d5}, [r1]!\n"
    182         // Accumulate a column
    183         "vadd.s32 q4, q4, q0\n"
    184         "vadd.s32 q8, q8, q1\n"
    185         "vadd.s32 q12, q12, q2\n"
    186 
    187         "add r0, %[dst_col_stride]\n"
    188         // Load a column
    189         "mov r1, r0\n"
    190         "vld1.32 {d0, d1}, [r1]!\n"
    191         "vld1.32 {d2, d3}, [r1]!\n"
    192         "vld1.32 {d4, d5}, [r1]!\n"
    193         // Accumulate a column
    194         "vadd.s32 q5, q5, q0\n"
    195         "vadd.s32 q9, q9, q1\n"
    196         "vadd.s32 q13, q13, q2\n"
    197 
    198         "add r0, %[dst_col_stride]\n"
    199         // Load a column
    200         "mov r1, r0\n"
    201         "vld1.32 {d0, d1}, [r1]!\n"
    202         "vld1.32 {d2, d3}, [r1]!\n"
    203         "vld1.32 {d4, d5}, [r1]!\n"
    204         // Accumulate a column
    205         "vadd.s32 q6, q6, q0\n"
    206         "vadd.s32 q10, q10, q1\n"
    207         "vadd.s32 q14, q14, q2\n"
    208 
    209         "add r0, %[dst_col_stride]\n"
    210         // Load a column
    211         "mov r1, r0\n"
    212         "vld1.32 {d0, d1}, [r1]!\n"
    213         "vld1.32 {d2, d3}, [r1]!\n"
    214         "vld1.32 {d4, d5}, [r1]!\n"
    215         // Accumulate a column
    216         "vadd.s32 q7, q7, q0\n"
    217         "vadd.s32 q11, q11, q1\n"
    218         "vadd.s32 q15, q15, q2\n"
    219 
    220         GEMMLOWP_STORE_RESULT_NEON_KERNEL_12X4_DEPTH2
    221         ":\n"
    222 
    223         "mov r0, %[dst_ptr]\n"
    224         // Store a column
    225         "mov r1, r0\n"
    226         "vst1.32 {d8, d9}, [r1]!\n"
    227         "vst1.32 {d16, d17}, [r1]!\n"
    228         "vst1.32 {d24, d25}, [r1]!\n"
    229         // Store a column
    230         "add r0, %[dst_col_stride]\n"
    231         "mov r1, r0\n"
    232         "vst1.32 {d10, d11}, [r1]!\n"
    233         "vst1.32 {d18, d19}, [r1]!\n"
    234         "vst1.32 {d26, d27}, [r1]!\n"
    235         // Store a column
    236         "add r0, %[dst_col_stride]\n"
    237         "mov r1, r0\n"
    238         "vst1.32 {d12, d13}, [r1]!\n"
    239         "vst1.32 {d20, d21}, [r1]!\n"
    240         "vst1.32 {d28, d29}, [r1]!\n"
    241         // Store a column
    242         "add r0, %[dst_col_stride]\n"
    243         "mov r1, r0\n"
    244         "vst1.32 {d14, d15}, [r1]!\n"
    245         "vst1.32 {d22, d23}, [r1]!\n"
    246         "vst1.32 {d30, d31}, [r1]!\n"
    247         :  // outputs
    248         [lhs_ptr] "+r"(lhs_ptr), [rhs_ptr] "+r"(rhs_ptr),
    249         [dst_ptr] "+r"(dst_ptr),
    250         [run_depth] "+r"(run_depth)
    251         :  // inputs
    252         [start_depth] "r"(start_depth),
    253         [dst_col_stride] "r"(dst_col_stride)
    254         :  // clobbers
    255         "cc", "memory", "r0", "r1",
    256         // note: someone on internet says that quad registers are
    257         // unsupported in the clobber list!
    258         "d0", "d1", "d2", "d3", "d4", "d5", "d6", "d7", "d8", "d9", "d10",
    259         "d11", "d12", "d13", "d14", "d15", "d16", "d17", "d18", "d19", "d20",
    260         "d21", "d22", "d23", "d24", "d25", "d26", "d27", "d28", "d29", "d30",
    261         "d31");
    262 #undef GEMMLOWP_LOOP_NEON_KERNEL_12X4_DEPTH2
    263 #undef GEMMLOWP_STORE_RESULT_NEON_KERNEL_12X4_DEPTH2
    264   }
    265 };
    266 
    267 struct NEON_32_Kernel12x4Depth2Assuming12BitProducts : KernelBase {
    268   typedef KernelFormat<
    269       KernelSideFormat<CellFormat<4, 2, CellOrder::WidthMajor>, 3>,
    270       KernelSideFormat<CellFormat<4, 2, CellOrder::WidthMajor>, 1> >
    271       Format;
    272 
    273   const char* Name() const override {
    274     return "NEON, 12x4, depth 2, assuming 12-bit products";
    275   }
    276 
    277   // TODO(benoitjacob): reorder function arguments so dst comes last
    278   void Run(std::int32_t* dst_ptr, std::size_t dst_row_stride,
    279            std::size_t dst_col_stride, const std::uint8_t* lhs_ptr,
    280            const std::uint8_t* rhs_ptr, std::size_t start_depth,
    281            std::size_t run_depth) const override {
    282     ScopedProfilingLabel label(
    283         "optimized kernel (NEON 12x4, assuming 12-bit products)");
    284     assert(dst_row_stride == 1);
    285 
    286 // See comments above for why we need local numerical labels in our asm.
    287 #define GEMMLOWP_LOOP_NEON_32_KERNEL_12X4_DEPTH2_ASSUMING_12BIT_PRODUCTS "1"
    288 #define GEMMLOWP_LOAD_GLOBAL_ACCUMULATORS_NEON_32_KERNEL_12X4_DEPTH2_12BIT "2"
    289 #define GEMMLOWP_LABEL_32 "3"
    290 #define GEMMLOWP_LABEL_24 "4"
    291 #define GEMMLOWP_LABEL_16 "5"
    292 #define GEMMLOWP_LABEL_8 "6"
    293 #define GEMMLOWP_LABEL_2 "7"
    294 
    295     // This kernel is special in that it uses local 16-bit accumulators.
    296     // Because it assumes that each product fits in 12 bits, it can accumulate
    297     // 16 products into a local 16-bit accumulator without risking overflow.
    298     // At that point, it must accumulate these local 16-bit accumulators back
    299     // into global 32-bit accumulators, which have to be stored in memory for
    300     // lack of register space.
    301     // This 12x4 block of global accumulators is laid out as 3 cells of size 4x4
    302     // stored in diagonal-major order like this for the first 4x4 cell:
    303     //
    304     //   0   4   8  12
    305     //  13   1   5   9
    306     //  10  14   2   6
    307     //   7  11  15   3
    308     //
    309     // and likewise for the 2nd  cell (16--31) and 3rd cell (32--47)
    310     std::int32_t global_accumulators[3 * 4 * 4];
    311     asm volatile(
    312         // Compute stride between consecutive columns, in bytes
    313         "mov r0, #4\n"  // multiply by 4 = sizeof(int32)
    314         "mul %[dst_col_stride], r0\n"
    315 
    316         "cmp %[start_depth], #0\n"
    317         "bne"
    318         " " GEMMLOWP_LOAD_GLOBAL_ACCUMULATORS_NEON_32_KERNEL_12X4_DEPTH2_12BIT
    319         "f\n"
    320 
    321         // If start_depth==0, we need to clear our global accumulators
    322         "mov r0, %[global_accumulators]\n"
    323         "vmov.s32 q8, #0\n"
    324         "vmov.s32 q9, q8\n"
    325         "vst1.32 {d16,d17,d18,d19}, [r0]!\n"
    326         "vst1.32 {d16,d17,d18,d19}, [r0]!\n"
    327         "vst1.32 {d16,d17,d18,d19}, [r0]!\n"
    328         "vst1.32 {d16,d17,d18,d19}, [r0]!\n"
    329         "vst1.32 {d16,d17,d18,d19}, [r0]!\n"
    330         "vst1.32 {d16,d17,d18,d19}, [r0]!\n"
    331         "b " GEMMLOWP_LOOP_NEON_32_KERNEL_12X4_DEPTH2_ASSUMING_12BIT_PRODUCTS
    332         "f\n"
    333 
    334         // If start_depth!=0, we need to load our existing global accumulators
    335         GEMMLOWP_LOAD_GLOBAL_ACCUMULATORS_NEON_32_KERNEL_12X4_DEPTH2_12BIT
    336         ":\n"
    337         // Load global accumulators from destination matrix, column-major
    338         "mov r1, %[dst_ptr]\n"
    339         "mov r0, %[dst_col_stride]\n"
    340         "sub r0, #32\n"
    341         "vld1.32 {d0,d1}, [r1]!\n"
    342         "vld1.32 {d8,d9}, [r1]!\n"
    343         "vld1.32 {d16,d17}, [r1], r0\n"
    344         "vld1.32 {d2,d3}, [r1]!\n"
    345         "vld1.32 {d10,d11}, [r1]!\n"
    346         "vld1.32 {d18,d19}, [r1], r0\n"
    347         "vld1.32 {d4,d5}, [r1]!\n"
    348         "vld1.32 {d12,d13}, [r1]!\n"
    349         "vld1.32 {d20,d21}, [r1], r0\n"
    350         "vld1.32 {d6,d7}, [r1]!\n"
    351         "vld1.32 {d14,d15}, [r1]!\n"
    352         "vld1.32 {d22,d23}, [r1], r0\n"
    353         // Now we need to convert the global accumulator registers to
    354         // 4x4-block-wise diagonal-major order. What we effectively want to do
    355         // is to rotate the rows, however the accumulators are stored in
    356         // column-major order in registers. So we achieve this by
    357         // transposing, rotating the registers, and transposing again each
    358         // 4x4 block.
    359         //
    360         // Transpose 3 4x4 blocks separately
    361         "vtrn.32 q0, q1\n"
    362         "vtrn.32 q2, q3\n"
    363         "vswp d1, d4\n"
    364         "vswp d3, d6\n"
    365         "vtrn.32 q4, q5\n"
    366         "vtrn.32 q6, q7\n"
    367         "vswp d9, d12\n"
    368         "vswp d11, d14\n"
    369         "vtrn.32 q8, q9\n"
    370         "vtrn.32 q10, q11\n"
    371         "vswp d17, d20\n"
    372         "vswp d19, d22\n"
    373         // Rotate the registers
    374         "vext.32 q1, q1, q1, #1\n"
    375         "vext.32 q2, q2, q2, #2\n"
    376         "vext.32 q3, q3, q3, #3\n"
    377         "vext.32 q5, q5, q5, #1\n"
    378         "vext.32 q6, q6, q6, #2\n"
    379         "vext.32 q7, q7, q7, #3\n"
    380         "vext.32 q9, q9, q9, #1\n"
    381         "vext.32 q10, q10, q10, #2\n"
    382         "vext.32 q11, q11, q11, #3\n"
    383         // Transpose again and store into our global accumulators
    384         // buffer. These two operations are done at once using vst4.
    385         "mov r0, %[global_accumulators]\n"
    386         "vst4.32 {d0,d2,d4,d6}, [r0]!\n"
    387         "vst4.32 {d1,d3,d5,d7}, [r0]!\n"
    388         "vst4.32 {d8,d10,d12,d14}, [r0]!\n"
    389         "vst4.32 {d9,d11,d13,d15}, [r0]!\n"
    390         "vst4.32 {d16,d18,d20,d22}, [r0]!\n"
    391         "vst4.32 {d17,d19,d21,d23}, [r0]!\n"
    392 
    393         /* Main loop */
    394 
    395         GEMMLOWP_LOOP_NEON_32_KERNEL_12X4_DEPTH2_ASSUMING_12BIT_PRODUCTS
    396         ":\n"
    397 
    398 // Overview of register layout:
    399 //
    400 // Registers q4--q16 are the local 16-bit accumulators.
    401 // However, each entry in the result matrix is represented
    402 // by *two* local 16-bit accumulators: one for even levels
    403 // of depth and one for odd levels of depth. These correspond
    404 // to the scalars at even and odd indices within each q-register.
    405 // Thus we effectively use 32 bits of register space for each
    406 // entry in the result matrix. The accumulators register layout
    407 // is the same as was described above for the global 32-bit
    408 // accumulators (3 cells of size 4x4 in diagonal-major order)
    409 // with the only difference that instead of 32bit values we have
    410 // pairs of 16bit values.
    411 //
    412 // A 2x4 cell of Rhs is stored in 8bit in d0.
    413 // A 12x2 block of 3 4x2 cells Lhs is stored in 8bit in d1--d3.
    414 //
    415 //                      +--------+--------+--------+--------+
    416 //                      |d0[0]   |d0[2]   |d0[4]   |d0[6]   |
    417 //                 Rhs  +--------+--------+--------+--------+
    418 //                      |d0[1]   |d0[3]   |d0[5]   |d0[7]   |
    419 //                      +--------+--------+--------+--------+
    420 //
    421 //                      |        |        |        |        |
    422 //
    423 //    Lhs               |        |        |        |        |
    424 //
    425 //  +-----+-----+ - - - +--------+--------+--------+--------+
    426 //  |d1[0]|d1[1]|       |q4[0,1] |q5[0,1] |q6[0,1] |q7[0,1] |
    427 //  |d1[2]|d1[3]|       |q7[2,3] |q4[2,3] |q5[2,3] |q6[2,3] |
    428 //  |d1[4]|d1[5]|       |q6[4,5] |q7[4,5] |q4[4,5] |q5[4,5] |
    429 //  |d1[6]|d1[7]|       |q5[6,7] |q6[6,7] |q7[6,7] |q4[6,7] |
    430 //  +-----+-----+ - - - +--------+--------+--------+--------+
    431 //  |d2[0]|d2[1]|       |q8[0,1] |q8[0,1] |q8[0,1] |q8[0,1] |
    432 //  |d2[2]|d2[3]|       |q9[2,3] |q9[2,3] |q9[2,3] |q9[2,3] |
    433 //  |d2[4]|d2[5]|       |q10[4,5]|q10[4,5]|q10[4,5]|q10[4,5]|
    434 //  |d2[6]|d2[7]|       |q11[6,7]|q11[6,7]|q11[6,7]|q11[6,7]|
    435 //  +-----+-----+ - - - +--------+--------+--------+--------+
    436 //  |d3[0]|d3[1]|       |q12[0,1]|q12[0,1]|q12[0,1]|q12[0,1]|
    437 //  |d3[2]|d3[3]|       |q13[2,3]|q13[2,3]|q13[2,3]|q13[2,3]|
    438 //  |d3[4]|d3[5]|       |q14[4,5]|q14[4,5]|q14[4,5]|q14[4,5]|
    439 //  |d3[6]|d3[7]|       |q15[6,7]|q15[6,7]|q15[6,7]|q15[6,7]|
    440 //  +-----+-----+ - - - +--------+--------+--------+--------+
    441 //
    442 //                            Local 16-bit accumulators
    443 //                         Note: 2 scalars per matrix entry
    444 
    445 #define GEMMLOWP_ACCUMULATE_2_LEVELS_OF_DEPTH \
    446   /* Load 3 Lhs cells of size 4x2 */          \
    447   "vld1.8 {d1,d2,d3}, [%[lhs_ptr]:64]!\n"     \
    448                                               \
    449   /* Load 1 Rhs cell of size 2x4 */           \
    450   "vld1.8 {d0}, [%[rhs_ptr]:64]!\n"           \
    451                                               \
    452   /* Multiply-accumulate */                   \
    453   "vmlal.u8 q4, d1, d0\n"                     \
    454   "vmlal.u8 q8, d2, d0\n"                     \
    455   "vmlal.u8 q12, d3, d0\n"                    \
    456   "vext.8 d0, d0, d0, #2\n"                   \
    457   "vmlal.u8 q5, d1, d0\n"                     \
    458   "vmlal.u8 q9, d2, d0\n"                     \
    459   "vmlal.u8 q13, d3, d0\n"                    \
    460   "vext.8 d0, d0, d0, #2\n"                   \
    461   "vmlal.u8 q6, d1, d0\n"                     \
    462   "vmlal.u8 q10, d2, d0\n"                    \
    463   "vmlal.u8 q14, d3, d0\n"                    \
    464   "vext.8 d0, d0, d0, #2\n"                   \
    465   "vmlal.u8 q7, d1, d0\n"                     \
    466   "vmlal.u8 q11, d2, d0\n"                    \
    467   "vmlal.u8 q15, d3, d0\n"                    \
    468                                               \
    469   "sub %[run_depth], #2\n"
    470 
    471 #define GEMMLOWP_ACCUMULATE_8_LEVELS_OF_DEPTH \
    472   GEMMLOWP_ACCUMULATE_2_LEVELS_OF_DEPTH       \
    473   GEMMLOWP_ACCUMULATE_2_LEVELS_OF_DEPTH       \
    474   GEMMLOWP_ACCUMULATE_2_LEVELS_OF_DEPTH       \
    475   GEMMLOWP_ACCUMULATE_2_LEVELS_OF_DEPTH
    476 
    477         // Clear local 16-bit accumulators
    478         "vmov.s32 q4, #0\n"
    479         "vmov.s32 q5, q4\n"
    480         "vmov.s32 q6, q4\n"
    481         "vmov.s32 q7, q4\n"
    482         "vmov.s32 q8, q4\n"
    483         "vmov.s32 q9, q4\n"
    484         "vmov.s32 q10, q4\n"
    485         "vmov.s32 q11, q4\n"
    486         "vmov.s32 q12, q4\n"
    487         "vmov.s32 q13, q4\n"
    488         "vmov.s32 q14, q4\n"
    489         "vmov.s32 q15, q4\n"
    490 
    491         // Select a suitable number of depth levels
    492         // to process at this iteration. TODO (benoitjacob) I guess that
    493         // someone who really knows asm should make this a jump table.
    494         "cmp %[run_depth], #32\n"
    495         "bge " GEMMLOWP_LABEL_32
    496         "f\n"
    497         "cmp %[run_depth], #24\n"
    498         "bge " GEMMLOWP_LABEL_24
    499         "f\n"
    500         "cmp %[run_depth], #16\n"
    501         "bge " GEMMLOWP_LABEL_16
    502         "f\n"
    503         "cmp %[run_depth], #8\n"
    504         "bge " GEMMLOWP_LABEL_8
    505         "f\n"
    506         "b " GEMMLOWP_LABEL_2 "f\n"
    507 
    508         GEMMLOWP_LABEL_32
    509         ":\n" GEMMLOWP_ACCUMULATE_8_LEVELS_OF_DEPTH GEMMLOWP_LABEL_24
    510         ":\n" GEMMLOWP_ACCUMULATE_8_LEVELS_OF_DEPTH GEMMLOWP_LABEL_16
    511         ":\n" GEMMLOWP_ACCUMULATE_8_LEVELS_OF_DEPTH GEMMLOWP_LABEL_8
    512         ":\n" GEMMLOWP_ACCUMULATE_2_LEVELS_OF_DEPTH
    513             GEMMLOWP_ACCUMULATE_2_LEVELS_OF_DEPTH
    514                 GEMMLOWP_ACCUMULATE_2_LEVELS_OF_DEPTH GEMMLOWP_LABEL_2
    515         ":\n" GEMMLOWP_ACCUMULATE_2_LEVELS_OF_DEPTH
    516 
    517         // Accumulate the local accumulators into the global accumulators.
    518         // This is about summing adjacent pairs of 16-bit scalars into
    519         // single 32-bit scalars, so we use pairwise long addition (vpadal).
    520         "mov r0, %[global_accumulators]\n"
    521         "mov r1, %[global_accumulators]\n"
    522         "vld1.32 {d0,d1,d2,d3}, [r0]!\n"
    523         "vld1.32 {d4,d5,d6,d7}, [r0]!\n"
    524         "vpadal.u16 q0, q4\n"
    525         "vpadal.u16 q1, q5\n"
    526         "vpadal.u16 q2, q6\n"
    527         "vpadal.u16 q3, q7\n"
    528         "vst1.32 {d0,d1,d2,d3}, [r1]!\n"
    529         "vst1.32 {d4,d5,d6,d7}, [r1]!\n"
    530         "vld1.32 {d0,d1,d2,d3}, [r0]!\n"
    531         "vld1.32 {d4,d5,d6,d7}, [r0]!\n"
    532         "vpadal.u16 q0, q8\n"
    533         "vpadal.u16 q1, q9\n"
    534         "vpadal.u16 q2, q10\n"
    535         "vpadal.u16 q3, q11\n"
    536         "vst1.32 {d0,d1,d2,d3}, [r1]!\n"
    537         "vst1.32 {d4,d5,d6,d7}, [r1]!\n"
    538         "vld1.32 {d0,d1,d2,d3}, [r0]!\n"
    539         "vld1.32 {d4,d5,d6,d7}, [r0]!\n"
    540         "vpadal.u16 q0, q12\n"
    541         "vpadal.u16 q1, q13\n"
    542         "vpadal.u16 q2, q14\n"
    543         "vpadal.u16 q3, q15\n"
    544         "vst1.32 {d0,d1,d2,d3}, [r1]!\n"
    545         "vst1.32 {d4,d5,d6,d7}, [r1]!\n"
    546 
    547         // Loop.
    548         "cmp %[run_depth], #0\n"
    549         "bne " GEMMLOWP_LOOP_NEON_32_KERNEL_12X4_DEPTH2_ASSUMING_12BIT_PRODUCTS
    550         "b\n"
    551 
    552 #undef GEMMLOWP_CLEAR_LOCAL_ACCUMULATORS
    553 #undef GEMMLOWP_ACCUMULATE_8_LEVELS_OF_DEPTH
    554 #undef GEMMLOWP_ACCUMULATE_2_LEVELS_OF_DEPTH
    555 #undef GEMMLOWP_ADD_TO_GLOBAL_ACCUMULATORS
    556 
    557         /* end of main loop */
    558 
    559         // Store the global accumulators to the destination matrix
    560         // (column-major)
    561         // This is the reverse of the steps that we followed at the beginning
    562         // when we load the global accumulators from the destination matrix.
    563         // The problem is the same: how to convert 4x4 blocks
    564         // between column-major and diagonal-major orders.
    565         // Like above, we do this by rotating rows, and we achieve that by
    566         // tranposing, rotating columns, and transposing again.
    567         //
    568         // Load and transpose 4x4 blocks of global accumulators
    569         // These two steps are done at once by the vld4 instruction.
    570         "mov r0, %[global_accumulators]\n"
    571         "vld4.32 {d0,d2,d4,d6}, [r0]!\n"
    572         "vld4.32 {d1,d3,d5,d7}, [r0]!\n"
    573         "vld4.32 {d8,d10,d12,d14}, [r0]!\n"
    574         "vld4.32 {d9,d11,d13,d15}, [r0]!\n"
    575         "vld4.32 {d16,d18,d20,d22}, [r0]!\n"
    576         "vld4.32 {d17,d19,d21,d23}, [r0]!\n"
    577         // Rotate the rows of each 4x4 block
    578         "vext.32 q1, q1, q1, #3\n"
    579         "vext.32 q2, q2, q2, #2\n"
    580         "vext.32 q3, q3, q3, #1\n"
    581         "vext.32 q5, q5, q5, #3\n"
    582         "vext.32 q6, q6, q6, #2\n"
    583         "vext.32 q7, q7, q7, #1\n"
    584         "vext.32 q9, q9, q9, #3\n"
    585         "vext.32 q10, q10, q10, #2\n"
    586         "vext.32 q11, q11, q11, #1\n"
    587         // Transpose again each 4x4 block
    588         "vtrn.32 q0, q1\n"
    589         "vtrn.32 q2, q3\n"
    590         "vswp d1, d4\n"
    591         "vswp d3, d6\n"
    592         "vtrn.32 q4, q5\n"
    593         "vtrn.32 q6, q7\n"
    594         "vswp d9, d12\n"
    595         "vswp d11, d14\n"
    596         "vtrn.32 q8, q9\n"
    597         "vtrn.32 q10, q11\n"
    598         "vswp d17, d20\n"
    599         "vswp d19, d22\n"
    600         // Store into the column-major destination matrix
    601         "mov r1, %[dst_ptr]\n"
    602         "mov r0, %[dst_col_stride]\n"
    603         "sub r0, #32\n"
    604         "vst1.32 {d0,d1}, [r1]!\n"
    605         "vst1.32 {d8,d9}, [r1]!\n"
    606         "vst1.32 {d16,d17}, [r1], r0\n"
    607         "vst1.32 {d2,d3}, [r1]!\n"
    608         "vst1.32 {d10,d11}, [r1]!\n"
    609         "vst1.32 {d18,d19}, [r1], r0\n"
    610         "vst1.32 {d4,d5}, [r1]!\n"
    611         "vst1.32 {d12,d13}, [r1]!\n"
    612         "vst1.32 {d20,d21}, [r1], r0\n"
    613         "vst1.32 {d6,d7}, [r1]!\n"
    614         "vst1.32 {d14,d15}, [r1]!\n"
    615         "vst1.32 {d22,d23}, [r1], r0\n"
    616         :  // outputs
    617         [lhs_ptr] "+r"(lhs_ptr), [rhs_ptr] "+r"(rhs_ptr),
    618         [dst_ptr] "+r"(dst_ptr),
    619         [run_depth] "+r"(run_depth)
    620         :  // inputs
    621         [start_depth] "r"(start_depth), [dst_col_stride] "r"(dst_col_stride),
    622         [global_accumulators] "r"(&global_accumulators[0])
    623         :  // clobbers
    624         "cc", "memory", "r0", "r1",
    625         // note: someone on internet says that quad registers are
    626         // unsupported in the clobber list!
    627         "d0", "d1", "d2", "d3", "d4", "d5", "d6", "d7", "d8", "d9", "d10",
    628         "d11", "d12", "d13", "d14", "d15", "d16", "d17", "d18", "d19", "d20",
    629         "d21", "d22", "d23", "d24", "d25", "d26", "d27", "d28", "d29", "d30",
    630         "d31");
    631 #undef GEMMLOWP_LOOP_NEON_32_KERNEL_12X4_DEPTH2_ASSUMING_12BIT_PRODUCTS
    632 #undef GEMMLOWP_LOAD_GLOBAL_ACCUMULATORS_NEON_32_KERNEL_12X4_DEPTH2_12BIT
    633 #undef GEMMLOWP_LABEL_32
    634 #undef GEMMLOWP_LABEL_24
    635 #undef GEMMLOWP_LABEL_16
    636 #undef GEMMLOWP_LABEL_8
    637 #undef GEMMLOWP_LABEL_2
    638   }
    639 };
    640 
    641 #endif  // GEMMLOWP_NEON_32
    642 
    643 // The kernels here are specifically arm 64bit assembly, not arm 32bit.
    644 #ifdef GEMMLOWP_NEON_64
    645 
    646 // Our main GEMM kernel.
    647 struct NEON_64_Kernel12x8Depth2 : KernelBase {
    648   typedef KernelFormat<KernelSideFormat<CellFormat<4, 2>, 3>,
    649                        KernelSideFormat<CellFormat<4, 2>, 2> >
    650       Format;
    651 
    652   const char* Name() const override { return "NEON, 12x8, depth 2"; }
    653 
    654   // TODO(benoitjacob): reorder function arguments so dst comes last
    655   void Run(std::int32_t* dst_ptr, std::size_t dst_row_stride,
    656            std::size_t dst_col_stride, const std::uint8_t* lhs_ptr,
    657            const std::uint8_t* rhs_ptr, std::size_t start_depth,
    658            std::size_t run_depth) const override {
    659     ScopedProfilingLabel label("optimized kernel (NEON 12x8)");
    660 // See comments above for why we need local numerical labels in our asm.
    661 #define GEMMLOWP_LOOP_NEON_64_KERNEL_12X8_DEPTH2 "1"
    662 #define GEMMLOWP_STORE_RESULT_NEON_64_KERNEL_12x8_DEPTH2 "2"
    663 
    664     assert(dst_row_stride == 1);
    665     asm volatile(
    666         // Clear accumulator registers (see layout below)
    667         "dup v8.4s, wzr\n"
    668         "dup v9.4s, wzr\n"
    669         "dup v10.4s, wzr\n"
    670         "dup v11.4s, wzr\n"
    671         "dup v12.4s, wzr\n"
    672         "dup v13.4s, wzr\n"
    673         "dup v14.4s, wzr\n"
    674         "dup v15.4s, wzr\n"
    675         "dup v16.4s, wzr\n"
    676         "dup v17.4s, wzr\n"
    677         "dup v18.4s, wzr\n"
    678         "dup v19.4s, wzr\n"
    679         "dup v20.4s, wzr\n"
    680         "dup v21.4s, wzr\n"
    681         "dup v22.4s, wzr\n"
    682         "dup v23.4s, wzr\n"
    683         "dup v24.4s, wzr\n"
    684         "dup v25.4s, wzr\n"
    685         "dup v26.4s, wzr\n"
    686         "dup v27.4s, wzr\n"
    687         "dup v28.4s, wzr\n"
    688         "dup v29.4s, wzr\n"
    689         "dup v30.4s, wzr\n"
    690         "dup v31.4s, wzr\n"
    691 
    692         /* Main loop */
    693 
    694         GEMMLOWP_LOOP_NEON_64_KERNEL_12X8_DEPTH2
    695         ":\n"
    696 
    697         // Overview of register layout:
    698         //
    699         // A 2x8 block of 2 2x4 cells of Rhs is stored in 16bit in v0--v1.
    700         // A 12x2 block of 3 4x2 cells Lhs is stored in 16bit in v2--v4.
    701         // A 12x8 block of accumulators is stored in 32bit in v8--v31.
    702         //
    703         //                         +--------+--------+-----+--------+--------+
    704         //                         |v0.h[0] |v0.h[1] | ... |v1.h[2] |v1.h[3] |
    705         //                    Rhs  +--------+--------+-----+--------+--------+
    706         //                         |v0.h[4] |v0.h[5] | ... |v1.h[6] |v1.h[7] |
    707         //                         +--------+--------+-----+--------+--------+
    708         //
    709         //                         |        |        |     |        |        |
    710         //
    711         //    Lhs                  |        |        |     |        |        |
    712         //
    713         //  +-------+-------+ - -  +--------+--------+-----+--------+--------+
    714         //  |v2.h[0]|v2.h[4]|      |v8.s[0] |v9.s[0] | ... |v14.s[0]|v15.s[0]|
    715         //  |v2.h[1]|v2.h[5]|      |v8.s[1] |v9.s[1] | ... |v14.s[1]|v15.s[1]|
    716         //  |v2.h[2]|v2.h[6]|      |v8.s[2] |v9.s[2] | ... |v14.s[2]|v15.s[2]|
    717         //  |v2.h[3]|v2.h[7]|      |v8.s[3] |v9.s[3] | ... |v14.s[3]|v15.s[3]|
    718         //  +-------+-------+ - -  +--------+--------+-----+--------+--------+
    719         //  |v3.h[0]|v3.h[4]|      |v16.s[0]|v17.s[0]| ... |v22.s[0]|v23.s[0]|
    720         //  |v3.h[1]|v3.h[5]|      |v16.s[1]|v17.s[1]| ... |v22.s[1]|v23.s[1]|
    721         //  |v3.h[2]|v3.h[6]|      |v16.s[2]|v17.s[2]| ... |v22.s[2]|v23.s[2]|
    722         //  |v3.h[3]|v3.h[7]|      |v16.s[3]|v17.s[3]| ... |v22.s[3]|v23.s[3]|
    723         //  +-------+-------+ - -  +--------+--------+-----+--------+--------+
    724         //  |v4.h[0]|v4.h[4]|      |v24.s[0]|v25.s[0]| ... |v30.s[0]|v31.s[0]|
    725         //  |v4.h[1]|v4.h[5]|      |v24.s[1]|v25.s[1]| ... |v30.s[1]|v31.s[1]|
    726         //  |v4.h[2]|v4.h[6]|      |v24.s[2]|v25.s[2]| ... |v30.s[2]|v31.s[2]|
    727         //  |v4.h[3]|v4.h[7]|      |v24.s[3]|v25.s[3]| ... |v30.s[3]|v31.s[3]|
    728         //  +-------+-------+ - -  +--------+--------+-----+--------+--------+
    729         //
    730         //                            Accumulator
    731 
    732         // Load 1 Rhs cell of size 2x8
    733         "ld1 {v0.8b}, [%[rhs_ptr]], #8\n"
    734         "ld1 {v1.8b}, [%[rhs_ptr]], #8\n"
    735 
    736         // Load 3 Lhs cells of size 4x2 each
    737         "ld1 {v2.8b}, [%[lhs_ptr]], #8\n"
    738         "ld1 {v3.8b}, [%[lhs_ptr]], #8\n"
    739         "ld1 {v4.8b}, [%[lhs_ptr]], #8\n"
    740 
    741         // Expand Lhs/Rhs cells to 16 bit.
    742         "uxtl v0.8h, v0.8b\n"
    743         "uxtl v1.8h, v1.8b\n"
    744         "uxtl v2.8h, v2.8b\n"
    745         "uxtl v3.8h, v3.8b\n"
    746         "uxtl v4.8h, v4.8b\n"
    747 
    748         // Multiply-accumulate, level of depth 0
    749         "umlal v8.4s, v2.4h, v0.h[0]\n"
    750         "umlal v9.4s, v2.4h, v0.h[1]\n"
    751         "umlal v10.4s, v2.4h, v0.h[2]\n"
    752         "umlal v11.4s, v2.4h, v0.h[3]\n"
    753         "umlal v12.4s, v2.4h, v1.h[0]\n"
    754         "umlal v13.4s, v2.4h, v1.h[1]\n"
    755         "umlal v14.4s, v2.4h, v1.h[2]\n"
    756         "umlal v15.4s, v2.4h, v1.h[3]\n"
    757         "umlal v16.4s, v3.4h, v0.h[0]\n"
    758         "umlal v17.4s, v3.4h, v0.h[1]\n"
    759         "umlal v18.4s, v3.4h, v0.h[2]\n"
    760         "umlal v19.4s, v3.4h, v0.h[3]\n"
    761         "umlal v20.4s, v3.4h, v1.h[0]\n"
    762         "umlal v21.4s, v3.4h, v1.h[1]\n"
    763         "umlal v22.4s, v3.4h, v1.h[2]\n"
    764         "umlal v23.4s, v3.4h, v1.h[3]\n"
    765         "umlal v24.4s, v4.4h, v0.h[0]\n"
    766         "umlal v25.4s, v4.4h, v0.h[1]\n"
    767         "umlal v26.4s, v4.4h, v0.h[2]\n"
    768         "umlal v27.4s, v4.4h, v0.h[3]\n"
    769         "umlal v28.4s, v4.4h, v1.h[0]\n"
    770         "umlal v29.4s, v4.4h, v1.h[1]\n"
    771         "umlal v30.4s, v4.4h, v1.h[2]\n"
    772         "umlal v31.4s, v4.4h, v1.h[3]\n"
    773 
    774         // Multiply-accumulate, level of depth 1
    775         "umlal2 v8.4s, v2.8h, v0.h[4]\n"
    776         "umlal2 v9.4s, v2.8h, v0.h[5]\n"
    777         "umlal2 v10.4s, v2.8h, v0.h[6]\n"
    778         "umlal2 v11.4s, v2.8h, v0.h[7]\n"
    779         "umlal2 v12.4s, v2.8h, v1.h[4]\n"
    780         "umlal2 v13.4s, v2.8h, v1.h[5]\n"
    781         "umlal2 v14.4s, v2.8h, v1.h[6]\n"
    782         "umlal2 v15.4s, v2.8h, v1.h[7]\n"
    783         "umlal2 v16.4s, v3.8h, v0.h[4]\n"
    784         "umlal2 v17.4s, v3.8h, v0.h[5]\n"
    785         "umlal2 v18.4s, v3.8h, v0.h[6]\n"
    786         "umlal2 v19.4s, v3.8h, v0.h[7]\n"
    787         "umlal2 v20.4s, v3.8h, v1.h[4]\n"
    788         "umlal2 v21.4s, v3.8h, v1.h[5]\n"
    789         "umlal2 v22.4s, v3.8h, v1.h[6]\n"
    790         "umlal2 v23.4s, v3.8h, v1.h[7]\n"
    791         "umlal2 v24.4s, v4.8h, v0.h[4]\n"
    792         "umlal2 v25.4s, v4.8h, v0.h[5]\n"
    793         "umlal2 v26.4s, v4.8h, v0.h[6]\n"
    794         "umlal2 v27.4s, v4.8h, v0.h[7]\n"
    795         "umlal2 v28.4s, v4.8h, v1.h[4]\n"
    796         "umlal2 v29.4s, v4.8h, v1.h[5]\n"
    797         "umlal2 v30.4s, v4.8h, v1.h[6]\n"
    798         "umlal2 v31.4s, v4.8h, v1.h[7]\n"
    799 
    800         // Loop. Decrement loop index (depth) by 2, since we just handled 2
    801         // levels of depth (Kernel::kDepth=2).
    802         "subs %[run_depth], %[run_depth], #2\n"
    803         "bne " GEMMLOWP_LOOP_NEON_64_KERNEL_12X8_DEPTH2
    804         "b\n"
    805 
    806         /* end of main loop */
    807 
    808         /* Accumulate our local accumulator registers into the destination block
    809            */
    810 
    811         // Compute stride between consecutive columns, in bytes
    812         "mov x0, #4\n"  // multiply by 4 = sizeof(int32)
    813         "mul %[dst_col_stride], %[dst_col_stride], x0\n"
    814 
    815         // If start_depth == 0, then there is no preexisting accumulator
    816         // to accumulate, so we can simply store our result.
    817         "cmp %[start_depth], #0\n"
    818         "beq " GEMMLOWP_STORE_RESULT_NEON_64_KERNEL_12x8_DEPTH2
    819         "f\n"
    820 
    821         "mov x0, %[dst_ptr]\n"
    822 
    823         // Load a column
    824         "mov x1, x0\n"
    825         "ld1 {v0.4s}, [x1], #16\n"
    826         "ld1 {v1.4s}, [x1], #16\n"
    827         "ld1 {v2.4s}, [x1], #16\n"
    828         // Accumulate a column
    829         "add v8.4s, v8.4s, v0.4s\n"
    830         "add v16.4s, v16.4s, v1.4s\n"
    831         "add v24.4s, v24.4s, v2.4s\n"
    832 
    833         "add x0, x0, %[dst_col_stride]\n"
    834         // Load a column
    835         "mov x1, x0\n"
    836         "ld1 {v0.4s}, [x1], #16\n"
    837         "ld1 {v1.4s}, [x1], #16\n"
    838         "ld1 {v2.4s}, [x1], #16\n"
    839         // Accumulate a column
    840         "add v9.4s, v9.4s, v0.4s\n"
    841         "add v17.4s, v17.4s, v1.4s\n"
    842         "add v25.4s, v25.4s, v2.4s\n"
    843 
    844         "add x0, x0, %[dst_col_stride]\n"
    845         // Load a column
    846         "mov x1, x0\n"
    847         "ld1 {v0.4s}, [x1], #16\n"
    848         "ld1 {v1.4s}, [x1], #16\n"
    849         "ld1 {v2.4s}, [x1], #16\n"
    850         // Accumulate a column
    851         "add v10.4s, v10.4s, v0.4s\n"
    852         "add v18.4s, v18.4s, v1.4s\n"
    853         "add v26.4s, v26.4s, v2.4s\n"
    854 
    855         "add x0, x0, %[dst_col_stride]\n"
    856         // Load a column
    857         "mov x1, x0\n"
    858         "ld1 {v0.4s}, [x1], #16\n"
    859         "ld1 {v1.4s}, [x1], #16\n"
    860         "ld1 {v2.4s}, [x1], #16\n"
    861         // Accumulate a column
    862         "add v11.4s, v11.4s, v0.4s\n"
    863         "add v19.4s, v19.4s, v1.4s\n"
    864         "add v27.4s, v27.4s, v2.4s\n"
    865 
    866         "add x0, x0, %[dst_col_stride]\n"
    867         // Load a column
    868         "mov x1, x0\n"
    869         "ld1 {v0.4s}, [x1], #16\n"
    870         "ld1 {v1.4s}, [x1], #16\n"
    871         "ld1 {v2.4s}, [x1], #16\n"
    872         // Accumulate a column
    873         "add v12.4s, v12.4s, v0.4s\n"
    874         "add v20.4s, v20.4s, v1.4s\n"
    875         "add v28.4s, v28.4s, v2.4s\n"
    876 
    877         "add x0, x0, %[dst_col_stride]\n"
    878         // Load a column
    879         "mov x1, x0\n"
    880         "ld1 {v0.4s}, [x1], #16\n"
    881         "ld1 {v1.4s}, [x1], #16\n"
    882         "ld1 {v2.4s}, [x1], #16\n"
    883         // Accumulate a column
    884         "add v13.4s, v13.4s, v0.4s\n"
    885         "add v21.4s, v21.4s, v1.4s\n"
    886         "add v29.4s, v29.4s, v2.4s\n"
    887 
    888         "add x0, x0, %[dst_col_stride]\n"
    889         // Load a column
    890         "mov x1, x0\n"
    891         "ld1 {v0.4s}, [x1], #16\n"
    892         "ld1 {v1.4s}, [x1], #16\n"
    893         "ld1 {v2.4s}, [x1], #16\n"
    894         // Accumulate a column
    895         "add v14.4s, v14.4s, v0.4s\n"
    896         "add v22.4s, v22.4s, v1.4s\n"
    897         "add v30.4s, v30.4s, v2.4s\n"
    898 
    899         "add x0, x0, %[dst_col_stride]\n"
    900         // Load a column
    901         "mov x1, x0\n"
    902         "ld1 {v0.4s}, [x1], #16\n"
    903         "ld1 {v1.4s}, [x1], #16\n"
    904         "ld1 {v2.4s}, [x1], #16\n"
    905         // Accumulate a column
    906         "add v15.4s, v15.4s, v0.4s\n"
    907         "add v23.4s, v23.4s, v1.4s\n"
    908         "add v31.4s, v31.4s, v2.4s\n"
    909 
    910         GEMMLOWP_STORE_RESULT_NEON_64_KERNEL_12x8_DEPTH2
    911         ":\n"
    912 
    913         "mov x0, %[dst_ptr]\n"
    914         // Store a column
    915         "mov x1, x0\n"
    916         "st1 {v8.4s}, [x1], #16\n"
    917         "st1 {v16.4s}, [x1], #16\n"
    918         "st1 {v24.4s}, [x1], #16\n"
    919         // Store a column
    920         "add x0, x0, %[dst_col_stride]\n"
    921         "mov x1, x0\n"
    922         "st1 {v9.4s}, [x1], #16\n"
    923         "st1 {v17.4s}, [x1], #16\n"
    924         "st1 {v25.4s}, [x1], #16\n"
    925         // Store a column
    926         "add x0, x0, %[dst_col_stride]\n"
    927         "mov x1, x0\n"
    928         "st1 {v10.4s}, [x1], #16\n"
    929         "st1 {v18.4s}, [x1], #16\n"
    930         "st1 {v26.4s}, [x1], #16\n"
    931         // Store a column
    932         "add x0, x0, %[dst_col_stride]\n"
    933         "mov x1, x0\n"
    934         "st1 {v11.4s}, [x1], #16\n"
    935         "st1 {v19.4s}, [x1], #16\n"
    936         "st1 {v27.4s}, [x1], #16\n"
    937         // Store a column
    938         "add x0, x0, %[dst_col_stride]\n"
    939         "mov x1, x0\n"
    940         "st1 {v12.4s}, [x1], #16\n"
    941         "st1 {v20.4s}, [x1], #16\n"
    942         "st1 {v28.4s}, [x1], #16\n"
    943         // Store a column
    944         "add x0, x0, %[dst_col_stride]\n"
    945         "mov x1, x0\n"
    946         "st1 {v13.4s}, [x1], #16\n"
    947         "st1 {v21.4s}, [x1], #16\n"
    948         "st1 {v29.4s}, [x1], #16\n"
    949         // Store a column
    950         "add x0, x0, %[dst_col_stride]\n"
    951         "mov x1, x0\n"
    952         "st1 {v14.4s}, [x1], #16\n"
    953         "st1 {v22.4s}, [x1], #16\n"
    954         "st1 {v30.4s}, [x1], #16\n"
    955         // Store a column
    956         "add x0, x0, %[dst_col_stride]\n"
    957         "mov x1, x0\n"
    958         "st1 {v15.4s}, [x1], #16\n"
    959         "st1 {v23.4s}, [x1], #16\n"
    960         "st1 {v31.4s}, [x1], #16\n"
    961         :  // outputs
    962         [lhs_ptr] "+r"(lhs_ptr), [rhs_ptr] "+r"(rhs_ptr),
    963         [dst_ptr] "+r"(dst_ptr),
    964         [run_depth] "+r"(run_depth)
    965         :  // inputs
    966         [start_depth] "r"(start_depth),
    967         [dst_col_stride] "r"(dst_col_stride)
    968         :  // clobbers
    969         "cc", "memory", "x0", "x1", "v0", "v1", "v2", "v3", "v4", "v5", "v6",
    970         "v7", "v8", "v9", "v10", "v11", "v12", "v13", "v14", "v15", "v16",
    971         "v17", "v18", "v19", "v20", "v21", "v22", "v23", "v24", "v25", "v26",
    972         "v27", "v28", "v29", "v30", "v31");
    973 #undef GEMMLOWP_LOOP_NEON_64_KERNEL_12X8_DEPTH2
    974 #undef GEMMLOWP_STORE_RESULT_NEON_64_KERNEL_12x8_DEPTH2
    975   }
    976 };
    977 
    978 #endif  // GEMMLOWP_NEON_64
    979 
    980 // Our main GEMV kernel.
    981 // Because our GEMV performance is low and not dominated by the kernel
    982 // at the moment, it's not worth optimizing too hard yet.
    983 // Using intrinsics allows us to write one implementation for both 32bit and
    984 // 64bit ARM, and should also perform OK here because the register pressure
    985 // is not so high in this GEMV kernel.
    986 // When/if we get serious about GEMV performance, we will want to
    987 // implement it to bypass packing altogether, and use source data in-place
    988 // with different GEMV kernels for row-major and column-major LHS.
    989 template <int Cells>
    990 struct NEONKernel4Nx1Depth2 : KernelBase {
    991   typedef KernelFormat<KernelSideFormat<CellFormat<4, 2>, Cells>,
    992                        KernelSideFormat<CellFormat<1, 2>, 1> >
    993       Format;
    994 
    995   const char* Name() const override { return "NEON intrinsics, 4Nx1, depth 2"; }
    996 
    997   void Run(std::int32_t* dst_ptr, std::size_t dst_row_stride,
    998            std::size_t dst_col_stride, const std::uint8_t* lhs_ptr,
    999            const std::uint8_t* rhs_ptr, std::size_t start_depth,
   1000            std::size_t run_depth) const override {
   1001     ScopedProfilingLabel label("optimized kernel (NEON 4Nx1)");
   1002 
   1003     assert(dst_row_stride == 1);
   1004 
   1005     // Clear accumulators
   1006     uint32x4_t acc[Cells];
   1007     for (int cell = 0; cell < Cells; cell++) {
   1008       acc[cell] = vdupq_n_u32(0);
   1009     }
   1010     // Main loop
   1011     for (std::size_t d = 0; d < run_depth; d += 2) {
   1012       // Load LHS cells
   1013       uint16x8_t lhs[Cells];
   1014       for (int cell = 0; cell < Cells; cell++) {
   1015         lhs[cell] = vmovl_u8(vld1_u8(lhs_ptr));
   1016         lhs_ptr += 8;
   1017       }
   1018       // Load RHS cell
   1019       uint16_t rhs0 = rhs_ptr[0];
   1020       uint16_t rhs1 = rhs_ptr[1];
   1021       rhs_ptr += 2;
   1022       // Multiply-accumulate, level of depth 0
   1023       for (int cell = 0; cell < Cells; cell++) {
   1024         acc[cell] = vmlal_n_u16(acc[cell], vget_low_u16(lhs[cell]), rhs0);
   1025       }
   1026       // Multiply-accumulate, level of depth 1
   1027       for (int cell = 0; cell < Cells; cell++) {
   1028         acc[cell] = vmlal_n_u16(acc[cell], vget_high_u16(lhs[cell]), rhs1);
   1029       }
   1030     }
   1031     // If start_depth is nonzero, accumulate with the existing accumulator
   1032     if (start_depth) {
   1033       for (int cell = 0; cell < Cells; cell++) {
   1034         acc[cell] = vaddq_u32(
   1035             acc[cell], vreinterpretq_u32_s32(vld1q_s32(dst_ptr + 4 * cell)));
   1036       }
   1037     }
   1038     // Store the accumulators
   1039     for (int cell = 0; cell < Cells; cell++) {
   1040       vst1q_s32(dst_ptr + 4 * cell, vreinterpretq_s32_u32(acc[cell]));
   1041     }
   1042   }
   1043 };
   1044 
   1045 }  // namespace gemmlowp
   1046 
   1047 #endif  // GEMMLOWP_INTERNAL_KERNEL_NEON_H_
   1048