freedreno/ir3: lower load_barycentric_at_sample

This lowers load_barycentric_at_sample to load_sample_pos_from_id plus
load_barycentric_at_offset.

Signed-off-by: Rob Clark <robdclark@chromium.org>

src/compiler/nir/nir_intrinsics.py

@@ -602,6 +602,13 @@ barycentric("at_sample", [1])
 # src[] = { offset.xy }.
 barycentric("at_offset", [2])
 
+# Load sample position:
+#
+# Takes a sample # and returns a sample position.  Used for lowering
+# interpolateAtSample() to interpolateAtOffset()
+intrinsic("load_sample_pos_from_id", src_comp=[1], dest_comp=2,
+          flags=[CAN_ELIMINATE, CAN_REORDER])
+
 # Load operations pull data from some piece of GPU memory.  All load
 # operations operate in terms of offsets into some piece of theoretical
 # memory.  Loads from externally visible memory (UBO and SSBO) simply take a

src/freedreno/ir3/ir3_nir.h

@@ -38,6 +38,7 @@ void ir3_nir_scan_driver_consts(nir_shader *shader, struct ir3_driver_const_layo
 bool ir3_nir_apply_trig_workarounds(nir_shader *shader);
 bool ir3_nir_lower_tg4_to_tex(nir_shader *shader);
 bool ir3_nir_lower_io_offsets(nir_shader *shader);
+bool ir3_nir_lower_load_barycentric_at_sample(nir_shader *shader);
 bool ir3_nir_move_varying_inputs(nir_shader *shader);
 
 const nir_shader_compiler_options * ir3_get_compiler_options(struct ir3_compiler *compiler);

src/freedreno/ir3/ir3_nir_lower_load_barycentric_at_sample.c

@@ -0,0 +1,130 @@
+/*
+ * Copyright © 2019 Google, Inc.
+ *
+ * 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 "ir3_nir.h"
+#include "compiler/nir/nir_builder.h"
+
+/**
+ * This pass lowers load_barycentric_at_sample to load_sample_pos_from_id
+ * plus load_barycentric_at_offset.
+ *
+ * It also lowers load_sample_pos to load_sample_pos_from_id, mostly because
+ * that needs to happen at the same early stage (before wpos_ytransform)
+ */
+
+static nir_ssa_def *
+load_sample_pos(nir_builder *b, nir_ssa_def *samp_id)
+{
+	nir_intrinsic_instr *load_sp =
+			nir_intrinsic_instr_create(b->shader,
+					nir_intrinsic_load_sample_pos_from_id);
+	load_sp->num_components = 2;
+	load_sp->src[0] = nir_src_for_ssa(samp_id);
+	nir_ssa_dest_init(&load_sp->instr, &load_sp->dest, 2, 32, NULL);
+	nir_builder_instr_insert(b, &load_sp->instr);
+
+	return &load_sp->dest.ssa;
+}
+
+static void
+lower_load_barycentric_at_sample(nir_builder *b, nir_intrinsic_instr *intr)
+{
+	nir_ssa_def *pos = load_sample_pos(b, intr->src[0].ssa);
+
+	nir_intrinsic_instr *load_bary_at_offset =
+			nir_intrinsic_instr_create(b->shader,
+					nir_intrinsic_load_barycentric_at_offset);
+	load_bary_at_offset->num_components = 2;
+	load_bary_at_offset->src[0] = nir_src_for_ssa(pos);
+	nir_ssa_dest_init(&load_bary_at_offset->instr,
+			&load_bary_at_offset->dest, 2, 32, NULL);
+	nir_builder_instr_insert(b, &load_bary_at_offset->instr);
+
+	nir_ssa_def_rewrite_uses(&intr->dest.ssa,
+			nir_src_for_ssa(&load_bary_at_offset->dest.ssa));
+}
+
+static void
+lower_load_sample_pos(nir_builder *b, nir_intrinsic_instr *intr)
+{
+	nir_ssa_def *pos = load_sample_pos(b, nir_load_sample_id(b));
+
+	/* Note that gl_SamplePosition is offset by +vec2(0.5, 0.5) vs the
+	 * offset passed to interpolateAtOffset().   See
+	 * dEQP-GLES31.functional.shaders.multisample_interpolation.interpolate_at_offset.at_sample_position.default_framebuffer
+	 * for example.
+	 */
+	nir_ssa_def *half = nir_imm_float(b, 0.5);
+	pos = nir_fadd(b, pos, nir_vec2(b, half, half));
+
+	nir_ssa_def_rewrite_uses(&intr->dest.ssa, nir_src_for_ssa(pos));
+}
+
+bool
+ir3_nir_lower_load_barycentric_at_sample(nir_shader *shader)
+{
+	bool progress = false;
+
+	debug_assert(shader->info.stage == MESA_SHADER_FRAGMENT);
+
+	nir_foreach_function (function, shader) {
+		if (!function->impl)
+			continue;
+
+		nir_builder b;
+		nir_builder_init(&b, function->impl);
+
+		nir_foreach_block (block, function->impl) {
+			nir_foreach_instr_safe(instr, block) {
+				if (instr->type != nir_instr_type_intrinsic)
+					continue;
+
+				nir_intrinsic_instr *intr = nir_instr_as_intrinsic(instr);
+
+				if (intr->intrinsic != nir_intrinsic_load_barycentric_at_sample &&
+						intr->intrinsic != nir_intrinsic_load_sample_pos)
+					continue;
+
+				debug_assert(intr->dest.is_ssa);
+
+				b.cursor = nir_before_instr(instr);
+
+				if (intr->intrinsic == nir_intrinsic_load_sample_pos) {
+					lower_load_sample_pos(&b, intr);
+				} else {
+					debug_assert(intr->src[0].is_ssa);
+					lower_load_barycentric_at_sample(&b, intr);
+				}
+
+				progress = true;
+			}
+		}
+
+		if (progress) {
+			nir_metadata_preserve(function->impl,
+				nir_metadata_block_index | nir_metadata_dominance);
+		}
+	}
+
+	return progress;
+}

src/freedreno/ir3/meson.build

@@ -51,6 +51,7 @@ libfreedreno_ir3_files = files(
   'ir3_nir.c',
   'ir3_nir.h',
   'ir3_nir_analyze_ubo_ranges.c',
+  'ir3_nir_lower_load_barycentric_at_sample.c',
   'ir3_nir_lower_io_offsets.c',
   'ir3_nir_lower_tg4_to_tex.c',
   'ir3_nir_move_varying_inputs.c',