src/compiler/nir/nir_split_var_copies.c

   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@jlekstrand.net)
  25  *
  26  */
  27
  28 #include "nir.h"
  29 #include "nir_builder.h"
  30
  31 /*
  32  * Implements "copy splitting" which is similar to structure splitting only
  33  * it works on copy operations rather than the datatypes themselves.  The
  34  * GLSL language allows you to copy one variable to another an entire
  35  * structure (which may contain arrays or other structures) at a time.
  36  * Normally, in a language such as C this would be handled by a "structure
  37  * splitting" pass that breaks up the structures.  Unfortunately for us,
  38  * structures used in inputs or outputs can't be split.  Therefore,
  39  * regardlesss of what we do, we have to be able to copy to/from
  40  * structures.
  41  *
  42  * The primary purpose of structure splitting is to allow you to better
  43  * optimize variable access and lower things to registers where you can.
  44  * The primary issue here is that, if you lower the copy to a bunch of
  45  * loads and stores, you loose a lot of information about the copy
  46  * operation that you would like to keep around.  To solve this problem, we
  47  * have a "copy splitting" pass that, instead of splitting the structures
  48  * or lowering the copy into loads and storres, splits the copy operation
  49  * into a bunch of copy operations one for each leaf of the structure tree.
  50  * If an intermediate array is encountered, it is referenced with a
  51  * wildcard reference to indicate that the entire array is to be copied.
  52  *
  53  * As things become direct, array copies may be able to be losslessly
  54  * lowered to having fewer and fewer wildcards.  However, until that
  55  * happens we want to keep the information about the arrays intact.
  56  *
  57  * Prior to the copy splitting pass, there are no wildcard references but
  58  * there may be incomplete references where the tail of the deref chain is
  59  * an array or a structure and not a specific element.  After the copy
  60  * splitting pass has completed, every variable deref will be a full-length
  61  * dereference pointing to a single leaf in the structure type tree with
  62  * possibly a few wildcard array dereferences.
  63  */
  64
  65 static void
  66 split_deref_copy_instr(nir_builder *b,
  67                        nir_deref_instr *dst, nir_deref_instr *src)
  68 {
  69    assert(glsl_get_bare_type(dst->type) ==
  70           glsl_get_bare_type(src->type));
  71    if (glsl_type_is_vector_or_scalar(src->type)) {
  72       nir_copy_deref(b, dst, src);
  73    } else if (glsl_type_is_struct_or_ifc(src->type)) {
  74       for (unsigned i = 0; i < glsl_get_length(src->type); i++) {
  75          split_deref_copy_instr(b, nir_build_deref_struct(b, dst, i),
  76                                    nir_build_deref_struct(b, src, i));
  77       }
  78    } else {
  79       assert(glsl_type_is_matrix(src->type) || glsl_type_is_array(src->type));
  80       split_deref_copy_instr(b, nir_build_deref_array_wildcard(b, dst),
  81                                 nir_build_deref_array_wildcard(b, src));
  82    }
  83 }
  84
  85 static bool
  86 split_var_copies_impl(nir_function_impl *impl)
  87 {
  88    bool progress = false;
  89
  90    nir_builder b;
  91    nir_builder_init(&b, impl);
  92
  93    nir_foreach_block(block, impl) {
  94       nir_foreach_instr_safe(instr, block) {
  95          if (instr->type != nir_instr_type_intrinsic)
  96             continue;
  97
  98          nir_intrinsic_instr *copy = nir_instr_as_intrinsic(instr);
  99          if (copy->intrinsic != nir_intrinsic_copy_deref)
 100             continue;
 101
 102          b.cursor = nir_instr_remove(&copy->instr);
 103
 104          nir_deref_instr *dst =
 105             nir_instr_as_deref(copy->src[0].ssa->parent_instr);
 106          nir_deref_instr *src =
 107             nir_instr_as_deref(copy->src[1].ssa->parent_instr);
 108          split_deref_copy_instr(&b, dst, src);
 109
 110          progress = true;
 111       }
 112    }
 113
 114    if (progress) {
 115       nir_metadata_preserve(impl, nir_metadata_block_index |
 116                                   nir_metadata_dominance);
 117    } else {
 118 #ifndef NDEBUG
 119       impl->valid_metadata &= ~nir_metadata_not_properly_reset;
 120 #endif
 121    }
 122
 123    return progress;
 124 }
 125
 126 bool
 127 nir_split_var_copies(nir_shader *shader)
 128 {
 129    bool progress = false;
 130
 131    nir_foreach_function(function, shader) {
 132       if (function->impl)
 133          progress = split_var_copies_impl(function->impl) || progress;
 134    }
 135
 136    return progress;
 137 }