--- /dev/null
+/*
+ * Copyright (C) 2019 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.
+ *
+ * Authors (Collabora):
+ * Alyssa Rosenzweig <alyssa.rosenzweig@collabora.com>
+ */
+
+#include "compiler.h"
+
+/* Derivatives in Midgard are implemented on the texture pipe, rather than the
+ * ALU pipe as suggested by NIR. The rationale is that normal texture
+ * instructions require (implicit) derivatives to be calculated anyway, so it
+ * makes sense to reuse the derivative logic. Thus, in addition to the usual
+ * texturing ops that calculate derivatives, there are two explicit texture ops
+ * dFdx/dFdy that perform differencing across helper invocations in either
+ * horizontal or vertical directions.
+ *
+ * One major caveat is that derivatives can only be calculated on up to a vec2
+ * at a time. This restriction presumably is to save some silicon, as 99% of
+ * derivatives will be vec2 (autocalculating mip levels of 2D texture
+ * coordinates). Admittedly I'm not sure why 3D textures can have their levels
+ * calculated automatically, umm... Pressing on.
+ *
+ * This caveat is handled in two steps. During the first pass (code
+ * generation), we generate texture ops 1:1 to the incoming NIR derivatives.
+ * This works for float/vec2 but not for vec3/vec4. A later lowering pass will
+ * scan for vec3/vec4 derivatives and lower (split) to multiple instructions.
+ * This pass is separated as we'll have to rewrite th e destination into a
+ * register (rather than SSA) and we'd rather do this after we have the whole
+ * IR in front of us to do it at once.
+ */
+
+static unsigned
+mir_derivative_op(nir_op op)
+{
+ switch (op) {
+ case nir_op_fddx:
+ case nir_op_fddx_fine:
+ case nir_op_fddx_coarse:
+ return TEXTURE_OP_DFDX;
+
+ case nir_op_fddy:
+ case nir_op_fddy_fine:
+ case nir_op_fddy_coarse:
+ return TEXTURE_OP_DFDY;
+
+ default:
+ unreachable("Invalid derivative op");
+ }
+}
+
+/* Returns true if a texturing op computes derivatives either explicitly or
+ * implicitly */
+
+bool
+mir_op_computes_derivatives(unsigned op)
+{
+ switch (op) {
+ case TEXTURE_OP_NORMAL:
+ case TEXTURE_OP_DFDX:
+ case TEXTURE_OP_DFDY:
+ return true;
+ default:
+ return false;
+ }
+}
+
+void
+midgard_emit_derivatives(compiler_context *ctx, nir_alu_instr *instr)
+{
+ /* Create texture instructions */
+
+ unsigned nr_components = nir_dest_num_components(instr->dest.dest);
+
+ midgard_instruction ins = {
+ .type = TAG_TEXTURE_4,
+ .mask = mask_of(nr_components),
+ .ssa_args = {
+ .dest = nir_dest_index(ctx, &instr->dest.dest),
+ .src0 = nir_alu_src_index(ctx, &instr->src[0]),
+ .src1 = -1,
+ },
+ .texture = {
+ .op = mir_derivative_op(instr->op),
+ .format = MALI_TEX_2D,
+ .swizzle = SWIZZLE_XYXX,
+ .in_reg_swizzle = SWIZZLE_XYXX,
+
+ .in_reg_full = 1,
+ .out_full = 1,
+ .sampler_type = MALI_SAMPLER_FLOAT,
+ }
+ };
+
+ if (!instr->dest.dest.is_ssa)
+ ins.mask &= instr->dest.write_mask;
+
+ emit_mir_instruction(ctx, ins);
+
+ /* TODO: Set .cont/.last automatically via dataflow analysis */
+ ctx->texture_op_count++;
+}
+
+void
+midgard_lower_derivatives(compiler_context *ctx, midgard_block *block)
+{
+ mir_foreach_instr_in_block_safe(block, ins) {
+ if (ins->type != TAG_TEXTURE_4) continue;
+ if (!OP_IS_DERIVATIVE(ins->texture.op)) continue;
+
+ /* Check if we need to split */
+
+ bool upper = ins->mask & 0b1100;
+ bool lower = ins->mask & 0b0011;
+
+ if (!(upper && lower)) continue;
+
+ /* Duplicate for dedicated upper instruction */
+
+ midgard_instruction dup;
+ memcpy(&dup, ins, sizeof(dup));
+
+ /* Fixup masks. Make original just lower and dupe just upper */
+
+ ins->mask &= 0b0011;
+ dup.mask &= 0b1100;
+
+ /* Fixup swizzles */
+ assert(ins->texture.swizzle == SWIZZLE_XYXX);
+ assert(ins->texture.in_reg_swizzle == SWIZZLE_XYXX);
+ dup.texture.swizzle = SWIZZLE_XXXY;
+ dup.texture.in_reg_swizzle = SWIZZLE_ZWWW;
+
+ /* Insert the new instruction */
+ mir_insert_instruction_before(mir_next_op(ins), dup);
+
+ /* TODO: Set .cont/.last automatically via dataflow analysis */
+ ctx->texture_op_count++;
+
+ /* We'll need both instructions to write to the same index, so
+ * rewrite to use a register */
+
+ unsigned new = make_compiler_temp_reg(ctx);
+ mir_rewrite_index(ctx, ins->ssa_args.dest, new);
+ }
+}
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