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|
/*
* nextpnr -- Next Generation Place and Route
*
* Copyright (C) 2018 Clifford Wolf <clifford@symbioticeda.com>
* Copyright (C) 2018 David Shah <david@symbioticeda.com>
*
* Simulated annealing implementation based on arachne-pnr
* Copyright (C) 2015-2018 Cotton Seed
*
* Permission to use, copy, modify, and/or distribute this software for any
* purpose with or without fee is hereby granted, provided that the above
* copyright notice and this permission notice appear in all copies.
*
* THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
* WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
* MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
* ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
* WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
* ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
* OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
*
*/
#include "place_sa.h"
#include <algorithm>
#include <cmath>
#include <iostream>
#include <limits>
#include <list>
#include <map>
#include <ostream>
#include <queue>
#include <set>
#include <stdarg.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <vector>
#include "arch_place.h"
#include "log.h"
NEXTPNR_NAMESPACE_BEGIN
typedef int64_t wirelen_t;
class SAPlacer
{
public:
SAPlacer(Context *ctx) : ctx(ctx)
{
checker = new PlaceValidityChecker(ctx);
int num_bel_types = 0;
for (auto bel : ctx->getBels()) {
int x, y;
bool gb;
ctx->estimatePosition(bel, x, y, gb);
BelType type = ctx->getBelType(bel);
int type_idx;
if (bel_types.find(type) == bel_types.end()) {
type_idx = num_bel_types++;
bel_types[type] = type_idx;
} else {
type_idx = bel_types.at(type);
}
if (int(fast_bels.size()) < type_idx + 1)
fast_bels.resize(type_idx + 1);
if (int(fast_bels.at(type_idx).size()) < (x + 1))
fast_bels.at(type_idx).resize(x + 1);
if (int(fast_bels.at(type_idx).at(x).size()) < (y + 1))
fast_bels.at(type_idx).at(x).resize(y + 1);
max_x = std::max(max_x, x);
max_y = std::max(max_y, y);
fast_bels.at(type_idx).at(x).at(y).push_back(bel);
}
diameter = std::max(max_x, max_y) + 1;
}
bool place()
{
log_break();
size_t placed_cells = 0;
// Initial constraints placer
for (auto cell_entry : ctx->cells) {
CellInfo *cell = cell_entry.second;
auto loc = cell->attrs.find(ctx->id("BEL"));
if (loc != cell->attrs.end()) {
std::string loc_name = loc->second;
BelId bel = ctx->getBelByName(ctx->id(loc_name));
if (bel == BelId()) {
log_error(
"No Bel named \'%s\' located for "
"this chip (processing BEL attribute on \'%s\')\n",
loc_name.c_str(), cell->name.c_str(ctx));
}
BelType bel_type = ctx->getBelType(bel);
if (bel_type != ctx->belTypeFromId(cell->type)) {
log_error("Bel \'%s\' of type \'%s\' does not match cell "
"\'%s\' of type \'%s\'",
loc_name.c_str(),
ctx->belTypeToId(bel_type).c_str(ctx),
cell->name.c_str(ctx), cell->type.c_str(ctx));
}
cell->bel = bel;
cell->belStrength = STRENGTH_USER;
ctx->bindBel(bel, cell->name);
locked_bels.insert(bel);
placed_cells++;
}
}
int constr_placed_cells = placed_cells;
log_info("Placed %d cells based on constraints.\n", int(placed_cells));
// Sort to-place cells for deterministic initial placement
std::vector<CellInfo *> autoplaced;
for (auto cell : ctx->cells) {
CellInfo *ci = cell.second;
if (ci->bel == BelId()) {
autoplaced.push_back(cell.second);
}
}
std::sort(autoplaced.begin(), autoplaced.end(),
[](CellInfo *a, CellInfo *b) { return a->name < b->name; });
ctx->shuffle(autoplaced);
// Place cells randomly initially
log_info("Creating initial placement for remaining %d cells.\n",
int(autoplaced.size()));
for (auto cell : autoplaced) {
place_initial(cell);
placed_cells++;
if ((placed_cells - constr_placed_cells) % 500 == 0)
log_info(" initial placement placed %d/%d cells\n",
int(placed_cells - constr_placed_cells),
int(autoplaced.size()));
}
if ((placed_cells - constr_placed_cells) % 500 != 0)
log_info(" initial placement placed %d/%d cells\n",
int(placed_cells - constr_placed_cells),
int(autoplaced.size()));
log_info("Running simulated annealing placer.\n");
// Calculate wirelength after initial placement
curr_wirelength = 0;
curr_tns = 0;
for (auto net : ctx->nets) {
wirelen_t wl = get_wirelength(net.second, curr_tns);
wirelengths[net.first] = wl;
curr_wirelength += wl;
}
int n_no_progress = 0;
double avg_wirelength = curr_wirelength;
temp = 10000;
// Main simulated annealing loop
for (int iter = 1;; iter++) {
n_move = n_accept = 0;
improved = false;
if (iter % 5 == 0 || iter == 1)
log_info(" at iteration #%d: temp = %f, wire length = "
"%.0f, est tns = %.02fns\n",
iter, temp, double(curr_wirelength), curr_tns);
for (int m = 0; m < 15; ++m) {
// Loop through all automatically placed cells
for (auto cell : autoplaced) {
// Find another random Bel for this cell
BelId try_bel = random_bel_for_cell(cell);
// If valid, try and swap to a new position and see if
// the new position is valid/worthwhile
if (try_bel != BelId() && try_bel != cell->bel)
try_swap_position(cell, try_bel);
}
}
// Heuristic to improve placement on the 8k
if (improved)
n_no_progress = 0;
else
n_no_progress++;
if (temp <= 1e-3 && n_no_progress >= 5) {
if (iter % 5 != 0)
log_info(
" at iteration #%d: temp = %f, wire length = %f\n",
iter, temp, double(curr_wirelength));
break;
}
double Raccept = double(n_accept) / double(n_move);
int M = std::max(max_x, max_y) + 1;
double upper = 0.6, lower = 0.4;
if (curr_wirelength < 0.95 * avg_wirelength) {
avg_wirelength = 0.8 * avg_wirelength + 0.2 * curr_wirelength;
} else {
if (Raccept >= 0.8) {
temp *= 0.7;
} else if (Raccept > upper) {
if (diameter < M)
diameter++;
else
temp *= 0.9;
} else if (Raccept > lower) {
temp *= 0.95;
} else {
// Raccept < 0.3
if (diameter > 1)
diameter--;
else
temp *= 0.8;
}
}
// Recalculate total wirelength entirely to avoid rounding errors
// accumulating over time
curr_wirelength = 0;
curr_tns = 0;
for (auto net : ctx->nets) {
wirelen_t wl = get_wirelength(net.second, curr_tns);
wirelengths[net.first] = wl;
curr_wirelength += wl;
}
}
// Final post-pacement validitiy check
for (auto bel : ctx->getBels()) {
IdString cell = ctx->getBelCell(bel, false);
if (!checker->isBelLocationValid(bel)) {
std::string cell_text = "no cell";
if (cell != IdString())
cell_text = std::string("cell '") + cell.str(ctx) + "'";
if (ctx->force) {
log_warning(
"post-placement validity check failed for Bel '%s' "
"(%s)\n",
ctx->getBelName(bel).c_str(ctx), cell_text.c_str());
} else {
log_error(
"post-placement validity check failed for Bel '%s' "
"(%s)\n",
ctx->getBelName(bel).c_str(ctx), cell_text.c_str());
}
}
}
return true;
}
private:
// Initial random placement
void place_initial(CellInfo *cell)
{
bool all_placed = false;
int iters = 25;
while (!all_placed) {
BelId best_bel = BelId();
uint64_t best_score = std::numeric_limits<uint64_t>::max(),
best_ripup_score = std::numeric_limits<uint64_t>::max();
CellInfo *ripup_target = nullptr;
BelId ripup_bel = BelId();
if (cell->bel != BelId()) {
ctx->unbindBel(cell->bel);
cell->bel = BelId();
}
BelType targetType = ctx->belTypeFromId(cell->type);
for (auto bel : ctx->getBels()) {
if (ctx->getBelType(bel) == targetType &&
checker->isValidBelForCell(cell, bel)) {
if (ctx->checkBelAvail(bel)) {
uint64_t score = ctx->rng64();
if (score <= best_score) {
best_score = score;
best_bel = bel;
}
} else {
uint64_t score = ctx->rng64();
if (score <= best_ripup_score) {
best_ripup_score = score;
ripup_target =
ctx->cells.at(ctx->getBelCell(bel, true));
ripup_bel = bel;
}
}
}
}
if (best_bel == BelId()) {
if (iters == 0 || ripup_bel == BelId())
log_error("failed to place cell '%s' of type '%s'\n",
cell->name.c_str(ctx), cell->type.c_str(ctx));
--iters;
ctx->unbindBel(ripup_target->bel);
ripup_target->bel = BelId();
best_bel = ripup_bel;
} else {
all_placed = true;
}
cell->bel = best_bel;
cell->belStrength = STRENGTH_WEAK;
ctx->bindBel(cell->bel, cell->name);
// Back annotate location
cell->attrs[ctx->id("BEL")] = ctx->getBelName(cell->bel).str(ctx);
cell = ripup_target;
}
}
// Get the total estimated wirelength for a net
wirelen_t get_wirelength(NetInfo *net, float &tns)
{
wirelen_t wirelength = 0;
int driver_x, driver_y;
bool driver_gb;
CellInfo *driver_cell = net->driver.cell;
if (!driver_cell)
return 0;
if (driver_cell->bel == BelId())
return 0;
ctx->estimatePosition(driver_cell->bel, driver_x, driver_y, driver_gb);
WireId drv_wire = ctx->getWireBelPin(
driver_cell->bel, ctx->portPinFromId(net->driver.port));
if (driver_gb)
return 0;
float worst_slack = 1000;
int xmin = driver_x, xmax = driver_x, ymin = driver_y, ymax = driver_y;
for (auto load : net->users) {
if (load.cell == nullptr)
continue;
CellInfo *load_cell = load.cell;
if (load_cell->bel == BelId())
continue;
WireId user_wire = ctx->getWireBelPin(
load_cell->bel, ctx->portPinFromId(load.port));
delay_t raw_wl = ctx->estimateDelay(drv_wire, user_wire);
float slack =
ctx->getDelayNS(load.budget) - ctx->getDelayNS(raw_wl);
if (slack < 0)
tns += slack;
worst_slack = std::min(slack, worst_slack);
int load_x, load_y;
bool load_gb;
ctx->estimatePosition(load_cell->bel, load_x, load_y, load_gb);
if (load_gb)
continue;
xmin = std::min(xmin, load_x);
ymin = std::min(ymin, load_y);
xmax = std::max(xmax, load_x);
ymax = std::max(ymax, load_y);
}
wirelength =
wirelen_t((((ymax - ymin) + (xmax - xmin)) *
std::min(5.0, (1.0 + std::exp(-worst_slack / 5)))));
return wirelength;
}
// Attempt a SA position swap, return true on success or false on failure
bool try_swap_position(CellInfo *cell, BelId newBel)
{
static std::unordered_set<NetInfo *> update;
static std::vector<std::pair<IdString, wirelen_t>> new_lengths;
new_lengths.clear();
update.clear();
BelId oldBel = cell->bel;
IdString other = ctx->getBelCell(newBel, true);
CellInfo *other_cell = nullptr;
wirelen_t new_wirelength = 0, delta;
ctx->unbindBel(oldBel);
if (other != IdString()) {
other_cell = ctx->cells[other];
ctx->unbindBel(newBel);
}
for (const auto &port : cell->ports)
if (port.second.net != nullptr)
update.insert(port.second.net);
if (other != IdString()) {
for (const auto &port : other_cell->ports)
if (port.second.net != nullptr)
update.insert(port.second.net);
}
ctx->bindBel(newBel, cell->name);
if (other != IdString()) {
ctx->bindBel(oldBel, other_cell->name);
}
if (!checker->isBelLocationValid(newBel) ||
((other != IdString() && !checker->isBelLocationValid(oldBel)))) {
ctx->unbindBel(newBel);
if (other != IdString())
ctx->unbindBel(oldBel);
goto swap_fail;
}
cell->bel = newBel;
if (other != IdString())
other_cell->bel = oldBel;
new_wirelength = curr_wirelength;
// Recalculate wirelengths for all nets touched by the peturbation
for (auto net : update) {
new_wirelength -= wirelengths.at(net->name);
float temp_tns = 0;
wirelen_t net_new_wl = get_wirelength(net, temp_tns);
new_wirelength += net_new_wl;
new_lengths.push_back(std::make_pair(net->name, net_new_wl));
}
delta = new_wirelength - curr_wirelength;
n_move++;
// SA acceptance criterea
if (delta < 0 || (temp > 1e-6 && (ctx->rng() / float(0x3fffffff)) <=
std::exp(-delta / temp))) {
n_accept++;
if (delta < 2)
improved = true;
} else {
if (other != IdString())
ctx->unbindBel(oldBel);
ctx->unbindBel(newBel);
goto swap_fail;
}
curr_wirelength = new_wirelength;
for (auto new_wl : new_lengths)
wirelengths.at(new_wl.first) = new_wl.second;
return true;
swap_fail:
ctx->bindBel(oldBel, cell->name);
cell->bel = oldBel;
if (other != IdString()) {
ctx->bindBel(newBel, other);
other_cell->bel = newBel;
}
return false;
}
// Find a random Bel of the correct type for a cell, within the specified
// diameter
BelId random_bel_for_cell(CellInfo *cell)
{
BelType targetType = ctx->belTypeFromId(cell->type);
int x, y;
bool gb;
ctx->estimatePosition(cell->bel, x, y, gb);
while (true) {
int nx = ctx->rng(2 * diameter + 1) + std::max(x - diameter, 0);
int ny = ctx->rng(2 * diameter + 1) + std::max(y - diameter, 0);
int beltype_idx = bel_types.at(targetType);
if (nx >= int(fast_bels.at(beltype_idx).size()))
continue;
if (ny >= int(fast_bels.at(beltype_idx).at(nx).size()))
continue;
const auto &fb = fast_bels.at(beltype_idx).at(nx).at(ny);
if (fb.size() == 0)
continue;
BelId bel = fb.at(ctx->rng(int(fb.size())));
if (locked_bels.find(bel) != locked_bels.end())
continue;
return bel;
}
}
Context *ctx;
std::unordered_map<IdString, wirelen_t> wirelengths;
wirelen_t curr_wirelength = std::numeric_limits<wirelen_t>::max();
float curr_tns = 0;
float temp = 1000;
bool improved = false;
int n_move, n_accept;
int diameter = 35, max_x = 1, max_y = 1;
std::unordered_map<BelType, int> bel_types;
std::vector<std::vector<std::vector<std::vector<BelId>>>> fast_bels;
std::unordered_set<BelId> locked_bels;
PlaceValidityChecker *checker;
};
bool place_design_sa(Context *ctx)
{
try {
SAPlacer placer(ctx);
placer.place();
log_info("Checksum: 0x%08x\n", ctx->checksum());
return true;
} catch (log_execution_error_exception) {
return false;
}
}
NEXTPNR_NAMESPACE_END
|