src/freedreno/vulkan/tu_nir_lower_multiview.c

   1 /*
   2  * Copyright © 2020 Valve Corporation
   3  * SPDX-License-Identifier: MIT
   4  */
   5
   6 #include "tu_private.h"
   7 #include "nir_builder.h"
   8
   9 /* Some a6xx variants cannot support a non-contiguous multiview mask. Instead,
  10  * inside the shader something like this needs to be inserted:
  11  *
  12  * gl_Position = ((1ull << gl_ViewIndex) & view_mask) ? gl_Position : vec4(0.);
  13  *
  14  * Scan backwards until we find the gl_Position write (there should only be
  15  * one).
  16  */
  17 static bool
  18 lower_multiview_mask(nir_function_impl *impl, uint32_t mask)
  19 {
  20    nir_builder b;
  21    nir_builder_init(&b, impl);
  22
  23    nir_foreach_block_reverse(block, impl) {
  24       nir_foreach_instr_reverse(instr, block) {
  25          if (instr->type != nir_instr_type_intrinsic)
  26             continue;
  27
  28          nir_intrinsic_instr *intrin = nir_instr_as_intrinsic(instr);
  29          if (intrin->intrinsic != nir_intrinsic_store_deref)
  30             continue;
  31
  32          nir_deref_instr *deref = nir_src_as_deref(intrin->src[0]);
  33          if (deref->mode != nir_var_shader_out)
  34             continue;
  35
  36          nir_variable *var = nir_deref_instr_get_variable(deref);
  37          if (var->data.location != VARYING_SLOT_POS)
  38             continue;
  39
  40          assert(intrin->src[1].is_ssa);
  41          nir_ssa_def *orig_src = intrin->src[1].ssa;
  42          b.cursor = nir_before_instr(instr);
  43
  44          /* ((1ull << gl_ViewIndex) & mask) != 0 */
  45          nir_ssa_def *cmp =
  46             nir_i2b(&b, nir_iand(&b, nir_imm_int(&b, mask),
  47                                   nir_ishl(&b, nir_imm_int(&b, 1),
  48                                            nir_load_view_index(&b))));
  49
  50          nir_ssa_def *src = nir_bcsel(&b, cmp, orig_src, nir_imm_float(&b, 0.));
  51          nir_instr_rewrite_src(instr, &intrin->src[1], nir_src_for_ssa(src));
  52
  53          nir_metadata_preserve(impl, nir_metadata_block_index |
  54                                      nir_metadata_dominance);
  55          return true;
  56       }
  57    }
  58
  59    nir_metadata_preserve(impl, nir_metadata_all);
  60    return false;
  61 }
  62
  63 bool
  64 tu_nir_lower_multiview(nir_shader *nir, uint32_t mask, struct tu_device *dev)
  65 {
  66    nir_function_impl *entrypoint = nir_shader_get_entrypoint(nir);
  67
  68    if (!dev->physical_device->supports_multiview_mask &&
  69        !util_is_power_of_two_or_zero(mask + 1)) {
  70       return lower_multiview_mask(entrypoint, mask);
  71    }
  72
  73    nir_metadata_preserve(entrypoint, nir_metadata_all);
  74    return false;
  75 }
  76