pan/midgard: Implement linearly-constrained register allocation
Signed-off-by: Alyssa Rosenzweig <alyssa.rosenzweig@collabora.com>
This commit is contained in:
Alyssa Rosenzweig
Tomeu Vizoso
parent
fd81916ee5
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66ad64d73d
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/*
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* Copyright (C) 2019 Collabora, Ltd.
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*
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* Permission is hereby granted, free of charge, to any person obtaining a
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* copy of this software and associated documentation files (the "Software"),
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* to deal in the Software without restriction, including without limitation
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* the rights to use, copy, modify, merge, publish, distribute, sublicense,
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* and/or sell copies of the Software, and to permit persons to whom the
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* Software is furnished to do so, subject to the following conditions:
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*
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* The above copyright notice and this permission notice (including the next
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* paragraph) shall be included in all copies or substantial portions of the
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* Software.
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*
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* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
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* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
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* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
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* THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
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* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
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* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
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* SOFTWARE.
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*
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* Authors (Collabora):
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* Alyssa Rosenzweig <alyssa.rosenzweig@collabora.com>
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*/
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#include <stdio.h>
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#include <assert.h>
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#include <stdlib.h>
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#include <string.h>
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#include <limits.h>
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#include "util/macros.h"
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#include "util/u_math.h"
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#include "lcra.h"
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/* This module is the reference implementation of "Linearly Constrained
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* Register Allocation". The paper is available in PDF form
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* (https://people.collabora.com/~alyssa/LCRA.pdf) as well as Markdown+LaTeX
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* (https://gitlab.freedesktop.org/alyssa/lcra/blob/master/LCRA.md)
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*/
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struct lcra_state *
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lcra_alloc_equations(
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unsigned node_count,
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unsigned min_alignment, unsigned max_alignment,
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unsigned bound, unsigned class_count)
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{
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struct lcra_state *l = calloc(1, sizeof(*l));
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l->node_count = node_count;
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l->class_count = class_count;
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l->bound = bound;
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l->alignment = calloc(sizeof(l->alignment[0]), node_count);
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l->linear = calloc(sizeof(l->linear[0]), node_count * node_count);
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l->modulus = calloc(sizeof(l->modulus[0]), node_count);
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l->class = calloc(sizeof(l->class[0]), node_count);
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l->class_start = calloc(sizeof(l->class_start[0]), class_count);
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l->class_disjoint = calloc(sizeof(l->class_disjoint[0]), class_count * class_count);
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l->class_size = calloc(sizeof(l->class_size[0]), class_count);
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l->spill_cost = calloc(sizeof(l->spill_cost[0]), node_count);
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l->solutions = calloc(sizeof(l->solutions[0]), node_count);
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memset(l->solutions, ~0, sizeof(l->solutions[0]) * node_count);
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return l;
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}
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void
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lcra_set_alignment(struct lcra_state *l, unsigned node, unsigned align_log2)
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{
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l->alignment[node] = align_log2 + 1;
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}
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void
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lcra_set_disjoint_class(struct lcra_state *l, unsigned c1, unsigned c2)
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{
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l->class_disjoint[(c1 * l->class_count) + c2] = true;
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l->class_disjoint[(c2 * l->class_count) + c1] = true;
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}
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void
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lcra_restrict_range(struct lcra_state *l, unsigned node, unsigned len)
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{
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if (l->alignment[node])
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l->modulus[node] = DIV_ROUND_UP(l->bound - len + 1, 1 << (l->alignment[node] - 1));
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}
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void
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lcra_add_node_interference(struct lcra_state *l, unsigned i, unsigned cmask_i, unsigned j, unsigned cmask_j)
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{
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if (i == j)
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return;
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if (l->class_disjoint[(l->class[i] * l->class_count) + l->class[j]])
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return;
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uint32_t constraint_fw = 0;
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uint32_t constraint_bw = 0;
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for (unsigned D = 0; D < 16; ++D) {
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if (cmask_i & (cmask_j << D)) {
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constraint_bw |= (1 << (15 + D));
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constraint_fw |= (1 << (15 - D));
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}
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if (cmask_i & (cmask_j >> D)) {
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constraint_fw |= (1 << (15 + D));
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constraint_bw |= (1 << (15 - D));
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}
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}
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l->linear[j * l->node_count + i] |= constraint_fw;
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l->linear[i * l->node_count + j] |= constraint_bw;
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}
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static bool
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lcra_test_linear(struct lcra_state *l, unsigned *solutions, unsigned i)
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{
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unsigned *row = &l->linear[i * l->node_count];
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signed constant = solutions[i];
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for (unsigned j = 0; j < l->node_count; ++j) {
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if (solutions[j] == ~0) continue;
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signed lhs = solutions[j] - constant;
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if (lhs < -15 || lhs > 15)
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continue;
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if (row[j] & (1 << (lhs + 15)))
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return false;
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}
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return true;
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}
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bool
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lcra_solve(struct lcra_state *l)
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{
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for (unsigned step = 0; step < l->node_count; ++step) {
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if (l->solutions[step] != ~0) continue;
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if (l->alignment[step] == 0) continue;
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unsigned _class = l->class[step];
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unsigned class_start = l->class_start[_class];
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unsigned shift = l->alignment[step] - 1;
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unsigned P = l->bound >> shift;
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unsigned Q = l->modulus[step];
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unsigned r_max = l->class_size[_class];
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unsigned k_max = r_max >> shift;
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unsigned m_max = k_max / P;
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bool succ = false;
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for (unsigned m = 0; m < m_max; ++m) {
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for (unsigned n = 0; n < Q; ++n) {
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l->solutions[step] = ((m * P + n) << shift) + class_start;
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succ = lcra_test_linear(l, l->solutions, step);
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if (succ) break;
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}
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if (succ) break;
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}
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/* Out of registers - prepare to spill */
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if (!succ) {
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l->spill_class = l->class[step];
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return false;
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}
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}
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return true;
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}
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/* Register spilling is implemented with a cost-benefit system. Costs are set
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* by the user. Benefits are calculated from the constraints. */
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void
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lcra_set_node_spill_cost(struct lcra_state *l, unsigned node, signed cost)
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{
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l->spill_cost[node] = cost;
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}
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/* Count along the lower triangle */
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static unsigned
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lcra_count_constraints(struct lcra_state *l, unsigned i)
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{
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unsigned count = 0;
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unsigned *constraints = &l->linear[i * l->node_count];
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for (unsigned j = 0; j < i; ++j)
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count += util_bitcount(constraints[j]);
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return count;
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}
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signed
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lcra_get_best_spill_node(struct lcra_state *l)
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{
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signed best_benefit = INT_MIN;
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signed best_node = -1;
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for (unsigned i = 0; i < l->node_count; ++i) {
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/* Find spillable nodes */
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if (l->class[i] != l->spill_class) continue;
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if (l->spill_cost[i] < 0) continue;
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/* Compute the benefit of spilling a node as the number of
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* constraints on the node plus the number of slots it occupies
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* minus a multiple of the cost. TODO: Come up with a formula
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* whose use I can justify beyond "it makes my shaderdb look
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* happy" */
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signed benefit = lcra_count_constraints(l, i);
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benefit -= l->spill_cost[i] * 2;
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if (benefit > best_benefit) {
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best_benefit = benefit;
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best_node = i;
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}
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}
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return best_node;
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}
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@ -0,0 +1,110 @@
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/*
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* Copyright (C) 2019 Collabora, Ltd.
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*
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* Permission is hereby granted, free of charge, to any person obtaining a
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* copy of this software and associated documentation files (the "Software"),
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* to deal in the Software without restriction, including without limitation
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* the rights to use, copy, modify, merge, publish, distribute, sublicense,
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* and/or sell copies of the Software, and to permit persons to whom the
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* Software is furnished to do so, subject to the following conditions:
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*
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* The above copyright notice and this permission notice (including the next
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* paragraph) shall be included in all copies or substantial portions of the
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* Software.
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*
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* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
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* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
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* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
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* THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
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* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
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* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
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* SOFTWARE.
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*
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* Authors (Collabora):
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* Alyssa Rosenzweig <alyssa.rosenzweig@collabora.com>
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*/
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#ifndef __LCRA_H
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#define __LCRA_H
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#include <stdbool.h>
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#include <stdint.h>
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struct lcra_state {
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unsigned node_count;
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/* Word boundary where vectors can't cross */
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unsigned bound;
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/* Alignment for node in log2(bytes)+1. Since alignment must be
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* non-negative power-of-two, the elements are strictly positive
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* integers. Zero is the sentinel for a missing node */
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unsigned *alignment;
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/* Linear constraints imposed. Nested array sized upfront, organized as
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* linear[node_left][node_right]. That is, calculate indices as:
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*
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* Each element is itself a bit field denoting whether (c_j - c_i) bias
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* is present or not, including negative biases.
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*
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* Note for Midgard, there are 16 components so the bias is in range
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* [-15, 15] so encoded by 32-bit field. */
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uint32_t *linear;
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/* Per node max modulus constraints */
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uint8_t *modulus;
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/* Classes allow nodes to be partitioned with a starting register.
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* Classes cannot interfere; that is, they are true partitions in the
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* usual sense of the word. class_count is the number of classes.
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* class[] is indexed by a node to get the mapped class. class_start is
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* biased to all solutions in the class. */
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unsigned class_count;
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unsigned *class;
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unsigned *class_start;
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unsigned *class_size;
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bool *class_disjoint;
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/* Before solving, forced registers; after solving, solutions. */
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unsigned *solutions;
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/* For register spilling, the costs to spill nodes (as set by the user)
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* are in spill_cost[], negative if a node is unspillable. Internally,
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* spill_class specifies which class to spill (whichever class failed
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* to allocate) */
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signed *spill_cost;
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unsigned spill_class;
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};
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struct lcra_state *
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lcra_alloc_equations(
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unsigned node_count,
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unsigned min_alignment, unsigned max_alignment,
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unsigned bound, unsigned class_count);
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void
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lcra_set_disjoint_class(struct lcra_state *l, unsigned c1, unsigned c2);
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void
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lcra_set_alignment(struct lcra_state *l, unsigned node, unsigned align_log2);
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void
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lcra_restrict_range(struct lcra_state *l, unsigned node, unsigned len);
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void
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lcra_add_node_interference(struct lcra_state *l, unsigned i, unsigned cmask_i, unsigned j, unsigned cmask_j);
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bool
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lcra_solve(struct lcra_state *l);
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void
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lcra_set_node_spill_cost(struct lcra_state *l, unsigned node, signed cost);
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signed
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lcra_get_best_spill_node(struct lcra_state *l);
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#endif
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@ -37,6 +37,7 @@ libpanfrost_midgard_files = files(
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'midgard_opt_float.c',
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'midgard_opt_perspective.c',
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'disassemble.c',
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'lcra.c'
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)
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midgard_nir_algebraic_c = custom_target(
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