--- /dev/null
+/*
+ * Copyright (C) 2022 Collabora Ltd.
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a
+ * copy of this software and associated documentation files (the "Software"),
+ * to deal in the Software without restriction, including without limitation
+ * the rights to use, copy, modify, merge, publish, distribute, sublicense,
+ * and/or sell copies of the Software, and to permit persons to whom the
+ * Software is furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice (including the next
+ * paragraph) shall be included in all copies or substantial portions of the
+ * Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
+ * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+ * SOFTWARE.
+ */
+
+#include "bifrost_nir.h"
+
+static void
+lower_xfb_output(nir_builder *b, nir_intrinsic_instr *intr,
+ unsigned start_component, unsigned num_components,
+ unsigned buffer, unsigned offset_words)
+{
+ assert(buffer < MAX_XFB_BUFFERS);
+ assert(nir_intrinsic_component(intr) == 0); // TODO
+
+ /* Transform feedback info in units of words, convert to bytes. */
+ uint16_t stride = b->shader->info.xfb_stride[buffer] * 4;
+ assert(stride != 0);
+
+ uint16_t offset = offset_words * 4;
+
+ nir_ssa_def *index = nir_iadd(b,
+ nir_imul(b, nir_load_instance_id(b),
+ nir_load_num_vertices(b)),
+ nir_load_vertex_id_zero_base(b));
+
+ nir_ssa_def *buf = nir_load_xfb_address(b, 64, .base = buffer);
+ nir_ssa_def *addr =
+ nir_iadd(b, buf, nir_u2u64(b,
+ nir_iadd_imm(b,
+ nir_imul_imm(b, index, stride),
+ offset)));
+
+ assert(intr->src[0].is_ssa && "must lower XFB before lowering SSA");
+ nir_ssa_def *src = intr->src[0].ssa;
+ nir_ssa_def *value = nir_channels(b, src, BITFIELD_MASK(num_components) << start_component);
+ nir_store_global(b, addr, 4, value, BITFIELD_MASK(num_components));
+}
+
+static bool
+lower_xfb(nir_builder *b, nir_instr *instr, UNUSED void *data)
+{
+ if (instr->type != nir_instr_type_intrinsic)
+ return false;
+
+ nir_intrinsic_instr *intr = nir_instr_as_intrinsic(instr);
+ if (intr->intrinsic != nir_intrinsic_store_output)
+ return false;
+
+ bool progress = false;
+
+ b->cursor = nir_before_instr(&intr->instr);
+
+ for (unsigned i = 0; i < 2; ++i) {
+ nir_io_xfb xfb = i ? nir_intrinsic_io_xfb2(intr) : nir_intrinsic_io_xfb(intr);
+ for (unsigned j = 0; j < 2; ++j) {
+ if (!xfb.out[j].num_components) continue;
+
+ lower_xfb_output(b, intr, i*2 + j,
+ xfb.out[j].num_components,
+ xfb.out[j].buffer,
+ xfb.out[j].offset);
+ progress = true;
+ }
+ }
+
+ nir_instr_remove(instr);
+ return progress;
+}
+
+bool
+bifrost_nir_lower_xfb(nir_shader *nir)
+{
+ return nir_shader_instructions_pass(nir, lower_xfb,
+ nir_metadata_block_index |
+ nir_metadata_dominance, NULL);
+}
+