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/*
* 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),
.dest = nir_dest_index(ctx, &instr->dest.dest),
.src = { nir_alu_src_index(ctx, &instr->src[0]), ~0, ~0 },
.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(ctx, 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->dest, new);
}
}
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