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      1 /*
      2  * Copyright  2014 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  * Authors:
     24  *    Jason Ekstrand (jason (at) jlekstrand.net)
     25  *
     26  */
     27 
     28 #include "nir_constant_expressions.h"
     29 #include <math.h>
     30 
     31 /*
     32  * Implements SSA-based constant folding.
     33  */
     34 
     35 struct constant_fold_state {
     36    void *mem_ctx;
     37    nir_function_impl *impl;
     38    bool progress;
     39 };
     40 
     41 static bool
     42 constant_fold_alu_instr(nir_alu_instr *instr, void *mem_ctx)
     43 {
     44    nir_const_value src[4];
     45 
     46    if (!instr->dest.dest.is_ssa)
     47       return false;
     48 
     49    /* In the case that any outputs/inputs have unsized types, then we need to
     50     * guess the bit-size. In this case, the validator ensures that all
     51     * bit-sizes match so we can just take the bit-size from first
     52     * output/input with an unsized type. If all the outputs/inputs are sized
     53     * then we don't need to guess the bit-size at all because the code we
     54     * generate for constant opcodes in this case already knows the sizes of
     55     * the types involved and does not need the provided bit-size for anything
     56     * (although it still requires to receive a valid bit-size).
     57     */
     58    unsigned bit_size = 0;
     59    if (!nir_alu_type_get_type_size(nir_op_infos[instr->op].output_type))
     60       bit_size = instr->dest.dest.ssa.bit_size;
     61 
     62    for (unsigned i = 0; i < nir_op_infos[instr->op].num_inputs; i++) {
     63       if (!instr->src[i].src.is_ssa)
     64          return false;
     65 
     66       if (bit_size == 0 &&
     67           !nir_alu_type_get_type_size(nir_op_infos[instr->op].input_sizes[i])) {
     68          bit_size = instr->src[i].src.ssa->bit_size;
     69       }
     70 
     71       nir_instr *src_instr = instr->src[i].src.ssa->parent_instr;
     72 
     73       if (src_instr->type != nir_instr_type_load_const)
     74          return false;
     75       nir_load_const_instr* load_const = nir_instr_as_load_const(src_instr);
     76 
     77       for (unsigned j = 0; j < nir_ssa_alu_instr_src_components(instr, i);
     78            j++) {
     79          if (load_const->def.bit_size == 64)
     80             src[i].u64[j] = load_const->value.u64[instr->src[i].swizzle[j]];
     81          else
     82             src[i].u32[j] = load_const->value.u32[instr->src[i].swizzle[j]];
     83       }
     84 
     85       /* We shouldn't have any source modifiers in the optimization loop. */
     86       assert(!instr->src[i].abs && !instr->src[i].negate);
     87    }
     88 
     89    if (bit_size == 0)
     90       bit_size = 32;
     91 
     92    /* We shouldn't have any saturate modifiers in the optimization loop. */
     93    assert(!instr->dest.saturate);
     94 
     95    nir_const_value dest =
     96       nir_eval_const_opcode(instr->op, instr->dest.dest.ssa.num_components,
     97                             bit_size, src);
     98 
     99    nir_load_const_instr *new_instr =
    100       nir_load_const_instr_create(mem_ctx,
    101                                   instr->dest.dest.ssa.num_components,
    102                                   instr->dest.dest.ssa.bit_size);
    103 
    104    new_instr->value = dest;
    105 
    106    nir_instr_insert_before(&instr->instr, &new_instr->instr);
    107 
    108    nir_ssa_def_rewrite_uses(&instr->dest.dest.ssa,
    109                             nir_src_for_ssa(&new_instr->def));
    110 
    111    nir_instr_remove(&instr->instr);
    112    ralloc_free(instr);
    113 
    114    return true;
    115 }
    116 
    117 static bool
    118 constant_fold_deref(nir_instr *instr, nir_deref_var *deref)
    119 {
    120    bool progress = false;
    121 
    122    for (nir_deref *tail = deref->deref.child; tail; tail = tail->child) {
    123       if (tail->deref_type != nir_deref_type_array)
    124          continue;
    125 
    126       nir_deref_array *arr = nir_deref_as_array(tail);
    127 
    128       if (arr->deref_array_type == nir_deref_array_type_indirect &&
    129           arr->indirect.is_ssa &&
    130           arr->indirect.ssa->parent_instr->type == nir_instr_type_load_const) {
    131          nir_load_const_instr *indirect =
    132             nir_instr_as_load_const(arr->indirect.ssa->parent_instr);
    133 
    134          arr->base_offset += indirect->value.u32[0];
    135 
    136          /* Clear out the source */
    137          nir_instr_rewrite_src(instr, &arr->indirect, nir_src_for_ssa(NULL));
    138 
    139          arr->deref_array_type = nir_deref_array_type_direct;
    140 
    141          progress = true;
    142       }
    143    }
    144 
    145    return progress;
    146 }
    147 
    148 static bool
    149 constant_fold_intrinsic_instr(nir_intrinsic_instr *instr)
    150 {
    151    bool progress = false;
    152 
    153    unsigned num_vars = nir_intrinsic_infos[instr->intrinsic].num_variables;
    154    for (unsigned i = 0; i < num_vars; i++) {
    155       progress |= constant_fold_deref(&instr->instr, instr->variables[i]);
    156    }
    157 
    158    if (instr->intrinsic == nir_intrinsic_discard_if) {
    159       nir_const_value *src_val = nir_src_as_const_value(instr->src[0]);
    160       if (src_val && src_val->u32[0] == 0) {
    161          nir_instr_remove(&instr->instr);
    162          progress = true;
    163       }
    164    }
    165 
    166    return progress;
    167 }
    168 
    169 static bool
    170 constant_fold_tex_instr(nir_tex_instr *instr)
    171 {
    172    bool progress = false;
    173 
    174    if (instr->texture)
    175       progress |= constant_fold_deref(&instr->instr, instr->texture);
    176 
    177    if (instr->sampler)
    178       progress |= constant_fold_deref(&instr->instr, instr->sampler);
    179 
    180    return progress;
    181 }
    182 
    183 static bool
    184 constant_fold_block(nir_block *block, void *mem_ctx)
    185 {
    186    bool progress = false;
    187 
    188    nir_foreach_instr_safe(instr, block) {
    189       switch (instr->type) {
    190       case nir_instr_type_alu:
    191          progress |= constant_fold_alu_instr(nir_instr_as_alu(instr), mem_ctx);
    192          break;
    193       case nir_instr_type_intrinsic:
    194          progress |=
    195             constant_fold_intrinsic_instr(nir_instr_as_intrinsic(instr));
    196          break;
    197       case nir_instr_type_tex:
    198          progress |= constant_fold_tex_instr(nir_instr_as_tex(instr));
    199          break;
    200       default:
    201          /* Don't know how to constant fold */
    202          break;
    203       }
    204    }
    205 
    206    return progress;
    207 }
    208 
    209 static bool
    210 nir_opt_constant_folding_impl(nir_function_impl *impl)
    211 {
    212    void *mem_ctx = ralloc_parent(impl);
    213    bool progress = false;
    214 
    215    nir_foreach_block(block, impl) {
    216       progress |= constant_fold_block(block, mem_ctx);
    217    }
    218 
    219    if (progress)
    220       nir_metadata_preserve(impl, nir_metadata_block_index |
    221                                   nir_metadata_dominance);
    222 
    223    return progress;
    224 }
    225 
    226 bool
    227 nir_opt_constant_folding(nir_shader *shader)
    228 {
    229    bool progress = false;
    230 
    231    nir_foreach_function(function, shader) {
    232       if (function->impl)
    233          progress |= nir_opt_constant_folding_impl(function->impl);
    234    }
    235 
    236    return progress;
    237 }
    238