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                        enum gl_access_qualifier dst_access,
  69                        enum gl_access_qualifier src_access)
  70 {
  71    assert(glsl_get_bare_type(dst->type) ==
  72           glsl_get_bare_type(src->type));
  73    if (glsl_type_is_vector_or_scalar(src->type)) {
  74       nir_copy_deref_with_access(b, dst, src, dst_access, src_access);
  75    } else if (glsl_type_is_struct_or_ifc(src->type)) {
  76       for (unsigned i = 0; i < glsl_get_length(src->type); i++) {
  77          split_deref_copy_instr(b, nir_build_deref_struct(b, dst, i),
  78                                    nir_build_deref_struct(b, src, i),
  79                                    dst_access, src_access);
  80       }
  81    } else {
  82       assert(glsl_type_is_matrix(src->type) || glsl_type_is_array(src->type));
  83       split_deref_copy_instr(b, nir_build_deref_array_wildcard(b, dst),
  84                                 nir_build_deref_array_wildcard(b, src),
  85                                 dst_access, src_access);
  86    }
  87 }
  88
  89 static bool
  90 split_var_copies_impl(nir_function_impl *impl)
  91 {
  92    bool progress = false;
  93
  94    nir_builder b;
  95    nir_builder_init(&b, impl);
  96
  97    nir_foreach_block(block, impl) {
  98       nir_foreach_instr_safe(instr, block) {
  99          if (instr->type != nir_instr_type_intrinsic)
 100             continue;
 101
 102          nir_intrinsic_instr *copy = nir_instr_as_intrinsic(instr);
 103          if (copy->intrinsic != nir_intrinsic_copy_deref)
 104             continue;
 105
 106          b.cursor = nir_instr_remove(&copy->instr);
 107
 108          nir_deref_instr *dst =
 109             nir_instr_as_deref(copy->src[0].ssa->parent_instr);
 110          nir_deref_instr *src =
 111             nir_instr_as_deref(copy->src[1].ssa->parent_instr);
 112          split_deref_copy_instr(&b, dst, src,
 113                                 nir_intrinsic_dst_access(copy),
 114                                 nir_intrinsic_src_access(copy));
 115
 116          progress = true;
 117       }
 118    }
 119
 120    if (progress) {
 121       nir_metadata_preserve(impl, nir_metadata_block_index |
 122                                   nir_metadata_dominance);
 123    } else {
 124       nir_metadata_preserve(impl, nir_metadata_all);
 125    }
 126
 127    return progress;
 128 }
 129
 130 bool
 131 nir_split_var_copies(nir_shader *shader)
 132 {
 133    bool progress = false;
 134
 135    nir_foreach_function(function, shader) {
 136       if (function->impl)
 137          progress = split_var_copies_impl(function->impl) || progress;
 138    }
 139
 140    return progress;
 141 }