src/compiler/nir/nir_lower_bit_size.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 "nir_builder.h"
  25
  26 /**
  27  * Some ALU operations may not be supported in hardware in specific bit-sizes.
  28  * This pass allows implementations to selectively lower such operations to
  29  * a bit-size that is supported natively and then converts the result back to
  30  * the original bit-size.
  31  */
  32
  33 static void
  34 lower_instr(nir_builder *bld, nir_alu_instr *alu, unsigned bit_size)
  35 {
  36    const nir_op op = alu->op;
  37    unsigned dst_bit_size = alu->dest.dest.ssa.bit_size;
  38
  39    bld->cursor = nir_before_instr(&alu->instr);
  40
  41    /* Convert each source to the requested bit-size */
  42    nir_ssa_def *srcs[NIR_MAX_VEC_COMPONENTS] = { NULL };
  43    for (unsigned i = 0; i < nir_op_infos[op].num_inputs; i++) {
  44       nir_ssa_def *src = nir_ssa_for_alu_src(bld, alu, i);
  45
  46       nir_alu_type type = nir_op_infos[op].input_types[i];
  47       if (nir_alu_type_get_type_size(type) == 0)
  48          src = nir_convert_to_bit_size(bld, src, type, bit_size);
  49
  50       if (i == 1 && (op == nir_op_ishl || op == nir_op_ishr || op == nir_op_ushr)) {
  51          assert(util_is_power_of_two_nonzero(dst_bit_size));
  52          src = nir_iand(bld, src, nir_imm_int(bld, dst_bit_size - 1));
  53       }
  54
  55       srcs[i] = src;
  56    }
  57
  58    /* Emit the lowered ALU instruction */
  59    nir_ssa_def *lowered_dst = NULL;
  60    if (op == nir_op_imul_high || op == nir_op_umul_high) {
  61       assert(dst_bit_size * 2 <= bit_size);
  62       nir_ssa_def *lowered_dst = nir_imul(bld, srcs[0], srcs[1]);
  63       if (nir_op_infos[op].output_type & nir_type_uint)
  64          lowered_dst = nir_ushr_imm(bld, lowered_dst, dst_bit_size);
  65       else
  66          lowered_dst = nir_ishr_imm(bld, lowered_dst, dst_bit_size);
  67    } else {
  68       lowered_dst = nir_build_alu_src_arr(bld, op, srcs);
  69    }
  70
  71
  72    /* Convert result back to the original bit-size */
  73    if (dst_bit_size != bit_size) {
  74       nir_alu_type type = nir_op_infos[op].output_type;
  75       nir_ssa_def *dst = nir_convert_to_bit_size(bld, lowered_dst, type, dst_bit_size);
  76       nir_ssa_def_rewrite_uses(&alu->dest.dest.ssa, nir_src_for_ssa(dst));
  77    } else {
  78       nir_ssa_def_rewrite_uses(&alu->dest.dest.ssa, nir_src_for_ssa(lowered_dst));
  79    }
  80 }
  81
  82 static bool
  83 lower_impl(nir_function_impl *impl,
  84            nir_lower_bit_size_callback callback,
  85            void *callback_data)
  86 {
  87    nir_builder b;
  88    nir_builder_init(&b, impl);
  89    bool progress = false;
  90
  91    nir_foreach_block(block, impl) {
  92       nir_foreach_instr_safe(instr, block) {
  93          if (instr->type != nir_instr_type_alu)
  94             continue;
  95
  96          nir_alu_instr *alu = nir_instr_as_alu(instr);
  97          assert(alu->dest.dest.is_ssa);
  98
  99          unsigned lower_bit_size = callback(alu, callback_data);
 100          if (lower_bit_size == 0)
 101             continue;
 102
 103          lower_instr(&b, alu, lower_bit_size);
 104          progress = true;
 105       }
 106    }
 107
 108    if (progress) {
 109       nir_metadata_preserve(impl, nir_metadata_block_index |
 110                                   nir_metadata_dominance);
 111    } else {
 112       nir_metadata_preserve(impl, nir_metadata_all);
 113    }
 114
 115    return progress;
 116 }
 117
 118 bool
 119 nir_lower_bit_size(nir_shader *shader,
 120                    nir_lower_bit_size_callback callback,
 121                    void *callback_data)
 122 {
 123    bool progress = false;
 124
 125    nir_foreach_function(function, shader) {
 126       if (function->impl)
 127          progress |= lower_impl(function->impl, callback, callback_data);
 128    }
 129
 130    return progress;
 131 }
 132
 133 static void
 134 split_phi(nir_builder *b, nir_phi_instr *phi)
 135 {
 136    nir_phi_instr *lowered[2] = {
 137       nir_phi_instr_create(b->shader),
 138       nir_phi_instr_create(b->shader)
 139    };
 140    int num_components = phi->dest.ssa.num_components;
 141    assert(phi->dest.ssa.bit_size == 64);
 142
 143    nir_foreach_phi_src(src, phi) {
 144       assert(num_components == src->src.ssa->num_components);
 145
 146       b->cursor = nir_before_src(&src->src, false);
 147
 148       nir_ssa_def *x = nir_unpack_64_2x32_split_x(b, src->src.ssa);
 149       nir_ssa_def *y = nir_unpack_64_2x32_split_y(b, src->src.ssa);
 150
 151       nir_phi_src *xsrc = rzalloc(lowered[0], nir_phi_src);
 152       xsrc->pred = src->pred;
 153       xsrc->src = nir_src_for_ssa(x);
 154       exec_list_push_tail(&lowered[0]->srcs, &xsrc->node);
 155
 156       nir_phi_src *ysrc = rzalloc(lowered[1], nir_phi_src);
 157       ysrc->pred = src->pred;
 158       ysrc->src = nir_src_for_ssa(y);
 159       exec_list_push_tail(&lowered[1]->srcs, &ysrc->node);
 160    }
 161
 162    nir_ssa_dest_init(&lowered[0]->instr, &lowered[0]->dest,
 163                      num_components, 32, NULL);
 164    nir_ssa_dest_init(&lowered[1]->instr, &lowered[1]->dest,
 165                      num_components, 32, NULL);
 166
 167    b->cursor = nir_before_instr(&phi->instr);
 168    nir_builder_instr_insert(b, &lowered[0]->instr);
 169    nir_builder_instr_insert(b, &lowered[1]->instr);
 170
 171    b->cursor = nir_after_phis(nir_cursor_current_block(b->cursor));
 172    nir_ssa_def *merged = nir_pack_64_2x32_split(b, &lowered[0]->dest.ssa, &lowered[1]->dest.ssa);
 173    nir_ssa_def_rewrite_uses(&phi->dest.ssa, nir_src_for_ssa(merged));
 174    nir_instr_remove(&phi->instr);
 175 }
 176
 177 static bool
 178 lower_64bit_phi_impl(nir_function_impl *impl)
 179 {
 180    nir_builder b;
 181    nir_builder_init(&b, impl);
 182    bool progress = false;
 183
 184    nir_foreach_block(block, impl) {
 185       nir_foreach_instr_safe(instr, block) {
 186          if (instr->type != nir_instr_type_phi)
 187             break;
 188
 189          nir_phi_instr *phi = nir_instr_as_phi(instr);
 190          assert(phi->dest.is_ssa);
 191
 192          if (phi->dest.ssa.bit_size <= 32)
 193             continue;
 194
 195          split_phi(&b, phi);
 196          progress = true;
 197       }
 198    }
 199
 200    if (progress) {
 201       nir_metadata_preserve(impl, nir_metadata_block_index |
 202                                   nir_metadata_dominance);
 203    } else {
 204       nir_metadata_preserve(impl, nir_metadata_all);
 205    }
 206
 207    return progress;
 208 }
 209
 210 bool
 211 nir_lower_64bit_phis(nir_shader *shader)
 212 {
 213    bool progress = false;
 214
 215    nir_foreach_function(function, shader) {
 216       if (function->impl)
 217          progress |= lower_64bit_phi_impl(function->impl);
 218    }
 219
 220    return progress;
 221 }