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Invert.

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This commit is contained in:
nella 2026-04-01 09:07:42 +02:00
parent 5f2407f449
commit 293feb55fa
1 changed files with 16 additions and 9 deletions
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25
passes/techmap/csa_tree.cc
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@ -91,7 +91,8 @@ struct AluInfo {
return GetSize(bi) == 1 && bi[0] == State::S0 && GetSize(ci) == 1 && ci[0] == State::S0;
}
// A cell is chainable if it's a plain add/sub with unused carries.
// Chainable cells are adds/subs with no carry usage, connected chainable
// cells form chains that can be replaced with CSA trees.
bool is_chainable(Cell* cell)
{
if (!(is_add(cell) || is_subtract(cell)))
@ -138,7 +139,7 @@ struct Rewriter
return consumer;
}
// Find cells that consumes another cell's output.
// Find cells that consume another cell's output.
dict<Cell*, Cell*> find_parents(const pool<Cell*>& candidates)
{
dict<Cell*, Cell*> parent_of;
@ -151,6 +152,17 @@ struct Rewriter
return parent_of;
}
std::pair<dict<Cell*, pool<Cell*>>, pool<Cell*>> invert_parent_map(const dict<Cell*, Cell*>& parent_of)
{
dict<Cell*, pool<Cell*>> children_of;
pool<Cell*> has_parent;
for (auto& [child, parent] : parent_of) {
children_of[parent].insert(child);
has_parent.insert(child);
}
return {children_of, has_parent};
}
pool<Cell*> collect_chain(Cell* root, const dict<Cell*, pool<Cell*>>& children_of)
{
pool<Cell*> chain;
@ -376,6 +388,7 @@ struct Rewriter
extended.push_back(s);
}
// Add correction for negated operands (-x = ~x + 1 so 1 per negation)
if (neg_compensation > 0)
extended.push_back(SigSpec(neg_compensation, width));
@ -402,13 +415,7 @@ struct Rewriter
return;
auto parent_of = find_parents(candidates);
dict<Cell*, pool<Cell*>> children_of;
pool<Cell*> has_parent;
for (auto& [child, parent] : parent_of) {
children_of[parent].insert(child);
has_parent.insert(child);
}
auto [children_of, has_parent] = invert_parent_map(parent_of);
pool<Cell*> processed;
for (auto root : candidates) {