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HeAP: Document legalise_placement_strict better

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Signed-off-by: gatecat <gatecat@ds0.me>
This commit is contained in:
gatecat 2021-02-23 10:53:35 +00:00
parent 20f0ba9526
commit 72b7a2e107
1 changed files with 45 additions and 3 deletions
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48
common/placer_heap.cc
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@ -222,6 +222,7 @@ class HeAPPlacer
// Heuristic: don't bother with threading below a certain size
auto solve_startt = std::chrono::high_resolution_clock::now();
// Build the connectivity matrix and run the solver; multithreaded between x and y axes if applicable
#ifndef NPNR_DISABLE_THREADS
if (solve_cells.size() >= 500) {
boost::thread xaxis([&]() { build_solve_direction(false, (iter == 0) ? -1 : iter); });
@ -240,6 +241,7 @@ class HeAPPlacer
update_all_chains();
// Run the spreader
for (const auto &group : cfg.cellGroups)
CutSpreader(this, group).run();
@ -248,6 +250,7 @@ class HeAPPlacer
[type](const std::unordered_set<BelBucketId> &grp) { return !grp.count(type); }))
CutSpreader(this, {type}).run();
// Run strict legalisation to find a valid bel for all cells
update_all_chains();
spread_hpwl = total_hpwl();
legalise_placement_strict(true);
@ -263,6 +266,7 @@ class HeAPPlacer
std::chrono::duration<double>(run_stopt - run_startt).count());
}
// Update timing weights
if (cfg.timing_driven)
get_criticalities(ctx, &net_crit);
@ -851,6 +855,8 @@ class HeAPPlacer
log_error("Unable to find legal placement for cell '%s', check constraints and utilisation.\n",
ctx->nameOf(ci));
// Determine a search radius around the solver location (which increases over time) that is clamped to
// the region constraint for the cell (if applicable)
int rx = radius, ry = radius;
if (ci->region != nullptr) {
@ -864,14 +870,18 @@ class HeAPPlacer
1);
}
// Pick a random X and Y location within our search radius
int nx = ctx->rng(2 * rx + 1) + std::max(cell_locs.at(ci->name).x - rx, 0);
int ny = ctx->rng(2 * ry + 1) + std::max(cell_locs.at(ci->name).y - ry, 0);
iter++;
iter_at_radius++;
if (iter >= (10 * (radius + 1))) {
// No luck yet, increase radius
radius = std::min(std::max(max_x, max_y), radius + 1);
while (radius < std::max(max_x, max_y)) {
// Keep increasing the radius until it will actually increase the number of cells we are
// checking (e.g. BRAM and DSP will not be in all cols/rows), so we don't waste effort
for (int x = std::max(0, cell_locs.at(ci->name).x - radius);
x <= std::min(max_x, cell_locs.at(ci->name).x + radius); x++) {
if (x >= int(fb->size()))
@ -890,6 +900,8 @@ class HeAPPlacer
iter_at_radius = 0;
iter = 0;
}
// If our randomly chosen cooridnate is out of bounds; or points to a tile with no relevant bels; ignore
// it
if (nx < 0 || nx > max_x)
continue;
if (ny < 0 || ny > max_y)
@ -902,8 +914,11 @@ class HeAPPlacer
if (fb->at(nx).at(ny).empty())
continue;
// The number of attempts to find a location to try
int need_to_explore = 2 * radius;
// If we have found at least one legal location; and made enough attempts; assume it's good enough and
// finish
if (iter_at_radius >= need_to_explore && bestBel != BelId()) {
CellInfo *bound = ctx->getBoundBelCell(bestBel);
if (bound != nullptr) {
@ -919,27 +934,38 @@ class HeAPPlacer
}
if (ci->constr_children.empty() && !ci->constr_abs_z) {
// The case where we have no relative constraints
for (auto sz : fb->at(nx).at(ny)) {
// Look through all bels in this tile; checking region constraint if applicable
if (ci->region != nullptr && ci->region->constr_bels && !ci->region->bels.count(sz))
continue;
// Prefer available bels; unless we are dealing with a wide radius (e.g. difficult control sets)
// or occasionally trigger a tiebreaker
if (ctx->checkBelAvail(sz) || (radius > ripup_radius || ctx->rng(20000) < 10)) {
CellInfo *bound = ctx->getBoundBelCell(sz);
if (bound != nullptr) {
// Only rip up cells without constraints
if (bound->constr_parent != nullptr || !bound->constr_children.empty() ||
bound->constr_abs_z)
continue;
ctx->unbindBel(bound->bel);
}
// Provisionally bind the bel
ctx->bindBel(sz, ci, STRENGTH_WEAK);
if (require_validity && !ctx->isBelLocationValid(sz)) {
// New location is not legal; unbind the cell (and rebind the cell we ripped up if
// applicable)
ctx->unbindBel(sz);
if (bound != nullptr)
ctx->bindBel(sz, bound, STRENGTH_WEAK);
} else if (iter_at_radius < need_to_explore) {
// It's legal, but we haven't tried enough locations yet
ctx->unbindBel(sz);
if (bound != nullptr)
ctx->bindBel(sz, bound, STRENGTH_WEAK);
int input_len = 0;
// Compute a fast input wirelength metric at this bel; and save if better than our last
// try
for (auto &port : ci->ports) {
auto &p = port.second;
if (p.type != PORT_IN || p.net == nullptr || p.net->driver.cell == nullptr)
@ -958,6 +984,7 @@ class HeAPPlacer
}
break;
} else {
// It's legal, and we've tried enough. Finish.
if (bound != nullptr)
remaining.emplace(chain_size[bound->name], bound->name);
Loc loc = ctx->getBelLocation(sz);
@ -969,33 +996,46 @@ class HeAPPlacer
}
}
} else {
// We do have relative constraints
for (auto sz : fb->at(nx).at(ny)) {
Loc loc = ctx->getBelLocation(sz);
// Check that the absolute-z constraint is satisfied if applicable
if (ci->constr_abs_z && loc.z != ci->constr_z)
continue;
// List of cells and their destination
std::vector<std::pair<CellInfo *, BelId>> targets;
// List of bels we placed things at; and the cell that was there before if applicable
std::vector<std::pair<BelId, CellInfo *>> swaps_made;
// List of (cell, new location) pairs to check
std::queue<std::pair<CellInfo *, Loc>> visit;
// FIXME: this approach of having a visit queue is designed to deal with recursively chained
// cells. But is this a case we really want to care about given the complexity it adds? Start by
// considering the root cell at the root location
visit.emplace(ci, loc);
while (!visit.empty()) {
CellInfo *vc = visit.front().first;
NPNR_ASSERT(vc->bel == BelId());
Loc ploc = visit.front().second;
visit.pop();
// Get the bel we're going to place this cell at
BelId target = ctx->getBelByLocation(ploc);
// Check it satisfies the region constraint if applicable
if (vc->region != nullptr && vc->region->constr_bels && !vc->region->bels.count(target))
goto fail;
CellInfo *bound;
// Check that the target bel exists and is of a suitable type
if (target == BelId() || !ctx->isValidBelForCellType(vc->type, target))
goto fail;
bound = ctx->getBoundBelCell(target);
// Chains cannot overlap
// Chains cannot overlap; so if we have to ripup a cell make sure it isn't part of a chain
if (bound != nullptr)
if (bound->constr_z != bound->UNCONSTR || bound->constr_parent != nullptr ||
!bound->constr_children.empty() || bound->belStrength > STRENGTH_WEAK)
goto fail;
targets.emplace_back(vc, target);
for (auto child : vc->constr_children) {
// For all the constrained children; compute the location we need to place them at and
// add them to the queue
Loc cloc = ploc;
if (child->constr_x != child->UNCONSTR)
cloc.x += child->constr_x;
@ -1006,7 +1046,7 @@ class HeAPPlacer
visit.emplace(child, cloc);
}
}
// Actually perform the move; keeping track of the moves we make so we can revert them if needed
for (auto &target : targets) {
CellInfo *bound = ctx->getBoundBelCell(target.second);
if (bound != nullptr)
@ -1014,7 +1054,7 @@ class HeAPPlacer
ctx->bindBel(target.second, target.first, STRENGTH_STRONG);
swaps_made.emplace_back(target.second, bound);
}
// Check that the move we have made is legal
for (auto &sm : swaps_made) {
if (!ctx->isBelLocationValid(sm.first))
goto fail;
@ -1022,6 +1062,7 @@ class HeAPPlacer
if (false) {
fail:
// If the move turned out to be illegal; revert all the moves we made
for (auto &swap : swaps_made) {
ctx->unbindBel(swap.first);
if (swap.second != nullptr)
@ -1036,6 +1077,7 @@ class HeAPPlacer
// log_info("%s %d %d %d\n", target.first->name.c_str(ctx), loc.x, loc.y, loc.z);
}
for (auto &swap : swaps_made) {
// Where we have ripped up cells; add them to the queue
if (swap.second != nullptr)
remaining.emplace(chain_size[swap.second->name], swap.second->name);
}