src/intel/compiler/brw_nir_tcs_workarounds.c

   1 /*
   2  * Copyright © 2016 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 "compiler/nir/nir_builder.h"
  25 #include "brw_nir.h"
  26
  27 /**
  28  * Implements the WaPreventHSTessLevelsInterference workaround (for Gen7-8).
  29  *
  30  * From the Broadwell PRM, Volume 7 (3D-Media-GPGPU), Page 494 (below the
  31  * definition of the patch header layouts):
  32  *
  33  *    "HW Bug: The Tessellation stage will incorrectly add domain points
  34  *     along patch edges under the following conditions, which may result
  35  *     in conformance failures and/or cracking artifacts:
  36  *
  37  *       * QUAD domain
  38  *       * INTEGER partitioning
  39  *       * All three TessFactors in a given U or V direction (e.g., V
  40  *         direction: UEQ0, InsideV, UEQ1) are all exactly 1.0
  41  *       * All three TessFactors in the other direction are > 1.0 and all
  42  *         round up to the same integer value (e.g, U direction:
  43  *         VEQ0 = 3.1, InsideU = 3.7, VEQ1 = 3.4)
  44  *
  45  *     The suggested workaround (to be implemented as part of the postamble
  46  *     to the HS shader in the HS kernel) is:
  47  *
  48  *     if (
  49  *        (TF[UEQ0] > 1.0) ||
  50  *        (TF[VEQ0] > 1.0) ||
  51  *        (TF[UEQ1] > 1.0) ||
  52  *        (TF[VEQ1] > 1.0) ||
  53  *        (TF[INSIDE_U] > 1.0) ||
  54  *        (TF[INSIDE_V] > 1.0) )
  55  *     {
  56  *        TF[INSIDE_U] = (TF[INSIDE_U] == 1.0) ? 2.0 : TF[INSIDE_U];
  57  *        TF[INSIDE_V] = (TF[INSIDE_V] == 1.0) ? 2.0 : TF[INSIDE_V];
  58  *     }"
  59  *
  60  * There's a subtlety here.  Intel internal HSD-ES bug 1208668495 notes
  61  * that the above workaround fails to fix certain GL/ES CTS tests which
  62  * have inside tessellation factors of -1.0.  This can be explained by
  63  * a quote from the ARB_tessellation_shader specification:
  64  *
  65  *    "If "equal_spacing" is used, the floating-point tessellation level is
  66  *     first clamped to the range [1,<max>], where <max> is implementation-
  67  *     dependent maximum tessellation level (MAX_TESS_GEN_LEVEL)."
  68  *
  69  * In other words, the actual inner tessellation factor used is
  70  * clamp(TF[INSIDE_*], 1.0, 64.0).  So we want to compare the clamped
  71  * value against 1.0.  To accomplish this, we change the comparison from
  72  * (TF[INSIDE_*] == 1.0) to (TF[INSIDE_*] <= 1.0).
  73  */
  74
  75 static inline nir_ssa_def *
  76 load_output(nir_builder *b, int num_components, int offset, int component)
  77 {
  78    nir_intrinsic_instr *load =
  79       nir_intrinsic_instr_create(b->shader, nir_intrinsic_load_output);
  80    nir_ssa_dest_init(&load->instr, &load->dest, num_components, 32, NULL);
  81    load->num_components = num_components;
  82    load->src[0] = nir_src_for_ssa(nir_imm_int(b, 0));
  83    nir_intrinsic_set_base(load, offset);
  84    nir_intrinsic_set_component(load, component);
  85
  86    nir_builder_instr_insert(b, &load->instr);
  87
  88    return &load->dest.ssa;
  89 }
  90
  91 static void
  92 emit_quads_workaround(nir_builder *b, nir_block *block)
  93 {
  94    b->cursor = nir_after_block_before_jump(block);
  95
  96    nir_ssa_def *inner = load_output(b, 2, 0, 2);
  97    nir_ssa_def *outer = load_output(b, 4, 1, 0);
  98
  99    nir_ssa_def *any_greater_than_1 =
 100        nir_ior(b, nir_bany(b, nir_flt(b, nir_imm_float(b, 1.0f), outer)),
 101                   nir_bany(b, nir_flt(b, nir_imm_float(b, 1.0f), inner)));
 102
 103    nir_if *if_stmt = nir_if_create(b->shader);
 104    if_stmt->condition = nir_src_for_ssa(any_greater_than_1);
 105    nir_builder_cf_insert(b, &if_stmt->cf_node);
 106
 107    /* Fill out the new then-block */
 108    b->cursor = nir_after_cf_list(&if_stmt->then_list);
 109
 110    inner = nir_bcsel(b, nir_fge(b, nir_imm_float(b, 1.0f), inner),
 111                         nir_imm_float(b, 2.0f), inner);
 112
 113    nir_intrinsic_instr *store =
 114       nir_intrinsic_instr_create(b->shader, nir_intrinsic_store_output);
 115    store->num_components = 2;
 116    nir_intrinsic_set_write_mask(store, WRITEMASK_XY);
 117    nir_intrinsic_set_component(store, 2);
 118    store->src[0] = nir_src_for_ssa(inner);
 119    store->src[1] = nir_src_for_ssa(nir_imm_int(b, 0));
 120    nir_builder_instr_insert(b, &store->instr);
 121 }
 122
 123 void
 124 brw_nir_apply_tcs_quads_workaround(nir_shader *nir)
 125 {
 126    assert(nir->stage == MESA_SHADER_TESS_CTRL);
 127
 128    nir_function_impl *impl = nir_shader_get_entrypoint(nir);
 129
 130    nir_builder b;
 131    nir_builder_init(&b, impl);
 132
 133    /* emit_quads_workaround() inserts an if statement into each block,
 134     * which splits it in two.  This changes the set of predecessors of
 135     * the end block.  We want to process the original set, so to be safe,
 136     * save it off to an array first.
 137     */
 138    const unsigned num_end_preds = impl->end_block->predecessors->entries;
 139    nir_block *end_preds[num_end_preds];
 140    unsigned i = 0;
 141    struct set_entry *entry;
 142
 143    set_foreach(impl->end_block->predecessors, entry) {
 144       end_preds[i++] = (nir_block *) entry->key;
 145    }
 146
 147    for (i = 0; i < num_end_preds; i++) {
 148       emit_quads_workaround(&b, end_preds[i]);
 149    }
 150
 151    nir_metadata_preserve(impl, 0);
 152 }