src/intel/compiler/brw_nir_lower_conversions.c

   1 /*
   2  * Copyright © 2018 Intel Corporation
   3  *
   4  * Permission is hereby granted, free of charge, to any person obtaining a
   5  * copy of this software and associated documentation files (the "Software"),
   6  * to deal in the Software without restriction, including without limitation
   7  * the rights to use, copy, modify, merge, publish, distribute, sublicense,
   8  * and/or sell copies of the Software, and to permit persons to whom the
   9  * Software is furnished to do so, subject to the following conditions:
  10  *
  11  * The above copyright notice and this permission notice (including the next
  12  * paragraph) shall be included in all copies or substantial portions of the
  13  * Software.
  14  *
  15  * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
  16  * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
  17  * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
  18  * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
  19  * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
  20  * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
  21  * IN THE SOFTWARE.
  22  */
  23
  24 #include "brw_nir.h"
  25 #include "compiler/nir/nir_builder.h"
  26
  27 static nir_op
  28 get_conversion_op(nir_alu_type src_type,
  29                   unsigned src_bit_size,
  30                   nir_alu_type dst_type,
  31                   unsigned dst_bit_size,
  32                   nir_rounding_mode rounding_mode)
  33 {
  34    nir_alu_type src_full_type = (nir_alu_type) (src_type | src_bit_size);
  35    nir_alu_type dst_full_type = (nir_alu_type) (dst_type | dst_bit_size);
  36
  37    return nir_type_conversion_op(src_full_type, dst_full_type, rounding_mode);
  38 }
  39
  40 static nir_rounding_mode
  41 get_opcode_rounding_mode(nir_op op)
  42 {
  43    switch (op) {
  44    case nir_op_f2f16_rtz:
  45       return nir_rounding_mode_rtz;
  46    case nir_op_f2f16_rtne:
  47       return nir_rounding_mode_rtne;
  48    default:
  49       return nir_rounding_mode_undef;
  50    }
  51 }
  52
  53 static void
  54 split_conversion(nir_builder *b, nir_alu_instr *alu, nir_op op1, nir_op op2)
  55 {
  56    b->cursor = nir_before_instr(&alu->instr);
  57    assert(alu->dest.write_mask == 1);
  58    nir_ssa_def *src = nir_ssa_for_alu_src(b, alu, 0);
  59    nir_ssa_def *tmp = nir_build_alu(b, op1, src, NULL, NULL, NULL);
  60    nir_ssa_def *res = nir_build_alu(b, op2, tmp, NULL, NULL, NULL);
  61    nir_ssa_def_rewrite_uses(&alu->dest.dest.ssa, nir_src_for_ssa(res));
  62    nir_instr_remove(&alu->instr);
  63 }
  64
  65 static bool
  66 lower_instr(nir_builder *b, nir_alu_instr *alu)
  67 {
  68    unsigned src_bit_size = nir_src_bit_size(alu->src[0].src);
  69    nir_alu_type src_type = nir_op_infos[alu->op].input_types[0];
  70    nir_alu_type src_full_type = (nir_alu_type) (src_type | src_bit_size);
  71
  72    unsigned dst_bit_size = nir_dest_bit_size(alu->dest.dest);
  73    nir_alu_type dst_full_type = nir_op_infos[alu->op].output_type;
  74    nir_alu_type dst_type = nir_alu_type_get_base_type(dst_full_type);
  75
  76    /* BDW PRM, vol02, Command Reference Instructions, mov - MOVE:
  77     *
  78     *   "There is no direct conversion from HF to DF or DF to HF.
  79     *    Use two instructions and F (Float) as an intermediate type.
  80     *
  81     *    There is no direct conversion from HF to Q/UQ or Q/UQ to HF.
  82     *    Use two instructions and F (Float) or a word integer type
  83     *    or a DWord integer type as an intermediate type."
  84     *
  85     * It is important that the intermediate conversion happens through a
  86     * 32-bit float type so we don't lose range when we convert from
  87     * a 64-bit integer.
  88     */
  89    if ((src_full_type == nir_type_float16 && dst_bit_size == 64) ||
  90        (src_bit_size == 64 && dst_full_type == nir_type_float16)) {
  91       nir_op op1 = get_conversion_op(src_type, src_bit_size,
  92                                      nir_type_float, 32,
  93                                      nir_rounding_mode_undef);
  94       nir_op op2 = get_conversion_op(nir_type_float, 32,
  95                                      dst_type, dst_bit_size,
  96                                      get_opcode_rounding_mode(alu->op));
  97       split_conversion(b, alu, op1, op2);
  98       return true;
  99    }
 100
 101    /* SKL PRM, vol 02a, Command Reference: Instructions, Move:
 102     *
 103     *   "There is no direct conversion from B/UB to DF or DF to B/UB. Use
 104     *    two instructions and a word or DWord intermediate type."
 105     *
 106     *   "There is no direct conversion from B/UB to Q/UQ or Q/UQ to B/UB.
 107     *    Use two instructions and a word or DWord intermediate integer
 108     *    type."
 109     *
 110     * It is important that we use a 32-bit integer matching the sign of the
 111     * destination as the intermediate type so we avoid any chance of rtne
 112     * rounding happening before the conversion to integer (which is expected
 113     * to round towards zero) in double to byte conversions.
 114     */
 115    if ((src_bit_size == 8 && dst_bit_size == 64) ||
 116        (src_bit_size == 64 && dst_bit_size == 8)) {
 117       nir_op op1 = get_conversion_op(src_type, src_bit_size, dst_type, 32,
 118                                      nir_rounding_mode_undef);
 119       nir_op op2 = get_conversion_op(dst_type, 32, dst_type, dst_bit_size,
 120                                      nir_rounding_mode_undef);
 121       split_conversion(b, alu, op1, op2);
 122       return true;
 123    }
 124
 125    return false;
 126 }
 127
 128 static bool
 129 lower_impl(nir_function_impl *impl)
 130 {
 131    nir_builder b;
 132    nir_builder_init(&b, impl);
 133    bool progress = false;
 134
 135    nir_foreach_block(block, impl) {
 136       nir_foreach_instr_safe(instr, block) {
 137          if (instr->type != nir_instr_type_alu)
 138             continue;
 139
 140          nir_alu_instr *alu = nir_instr_as_alu(instr);
 141          assert(alu->dest.dest.is_ssa);
 142
 143          if (!nir_op_infos[alu->op].is_conversion)
 144             continue;
 145
 146          progress = lower_instr(&b, alu) || progress;
 147       }
 148    }
 149
 150    if (progress) {
 151       nir_metadata_preserve(impl, nir_metadata_block_index |
 152                                   nir_metadata_dominance);
 153    } else {
 154       nir_metadata_preserve(impl, nir_metadata_all);
 155    }
 156
 157    return progress;
 158 }
 159
 160 bool
 161 brw_nir_lower_conversions(nir_shader *shader)
 162 {
 163    bool progress = false;
 164
 165    nir_foreach_function(function, shader) {
 166       if (function->impl)
 167          progress |= lower_impl(function->impl);
 168    }
 169
 170    return progress;
 171 }