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opt_muxtree: inhibit opt on reconvergence

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This commit is contained in:
Emil J. Tywoniak 2026-06-15 16:55:25 +02:00
parent 709149c42a
commit 7d942b9893
1 changed files with 22 additions and 14 deletions
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36
passes/opt/opt_muxtree.cc
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@ -34,7 +34,7 @@ PRIVATE_NAMESPACE_BEGIN
* A multiplexer tree (mux tree) is a tree composed exclusively of muxes.
* By mux, I mean $mux or $pmux. By port, I usually mean input port.
* The children of a node are all the muxes driving its input ports (A, B).
* It must be rooted in a "root mux", a mux which has multiple mux users
* It must be rooted in a "root mux", a mux which has multiple mux port users
* or any number of non-mux users. Only the root and leaf nodes can be
* root muxes, not the internal nodes. Leaf nodes that are root muxes
* are roots of "input trees".
@ -64,10 +64,17 @@ struct OptMuxtreeWorker
int removed_count;
int glob_evals_left = 10'000'000;
struct MuxPort {
int mux;
// Hacky: -1 is port A, if positive then indexes B port slices (of which $mux has only one)
int port;
inline Hasher hash_into(Hasher h) const { h.eat(mux); h.eat(port); return h; }
bool operator==(const MuxPort &other) const { return mux == other.mux && port == other.port; }
};
struct bitinfo_t {
// Is bit directly used by non-mux cells or ports?
bool seen_non_mux;
pool<int> mux_users;
pool<struct MuxPort> mux_users;
std::optional<int> mux_driver;
};
@ -94,10 +101,10 @@ struct OptMuxtreeWorker
vector<bool> root_enable_muxes;
pool<int> root_mux_rerun;
portinfo_t used_port_bit(RTLIL::SigSpec& sig, int mux_idx) {
portinfo_t used_port_bit(RTLIL::SigSpec& sig, int mux_idx, int port_idx) {
portinfo_t portinfo = {};
for (int bit_idx : sig2bits(sig)) {
bit2info[bit_idx].mux_users.insert(mux_idx);
bit2info[bit_idx].mux_users.insert({mux_idx, port_idx});
portinfo.input_sigs.insert(bit_idx);
}
return portinfo;
@ -127,7 +134,7 @@ struct OptMuxtreeWorker
for (int i = 0; i < GetSize(sig_s); i++) {
RTLIL::SigSpec sig = sig_b.extract(i*GetSize(sig_a), GetSize(sig_a));
RTLIL::SigSpec ctrl_sig = assign_map(SigSpec{sig_s[i]});
portinfo_t portinfo = used_port_bit(sig, this_mux_idx);
portinfo_t portinfo = used_port_bit(sig, this_mux_idx, i);
portinfo.ctrl_sig = sig2bits(ctrl_sig, false).front();
portinfo.const_activated = ctrl_sig.is_fully_const() && ctrl_sig.as_bool();
portinfo.const_deactivated = ctrl_sig.is_fully_const() && !ctrl_sig.as_bool();
@ -135,7 +142,7 @@ struct OptMuxtreeWorker
}
// Analyze port A
muxinfo.ports.push_back(used_port_bit(sig_a, this_mux_idx));
muxinfo.ports.push_back(used_port_bit(sig_a, this_mux_idx, -1));
for (int idx : sig2bits(sig_y)) {
if (bit2info[idx].mux_driver)
@ -170,17 +177,18 @@ struct OptMuxtreeWorker
// bit2info knows the mux users and mux drivers of bits
// use this to tell mux2info ports about what muxes are driven by it
for (int i = 0; i < GetSize(bit2info); i++)
for (int j : bit2info[i].mux_users)
for (auto &p : mux2info[j].ports) {
if (p.input_sigs.count(i))
if (bit2info[i].mux_driver)
p.input_muxes.insert(*bit2info[i].mux_driver);
for (auto muxport : bit2info[i].mux_users) {
for (auto &p : mux2info[muxport.mux].ports) {
if (p.input_sigs.count(i))
if (bit2info[i].mux_driver)
p.input_muxes.insert(*bit2info[i].mux_driver);
}
}
}
void populate_roots() {
// mux_to_users[i] means "set of muxes using output of mux i"
dict<int, pool<int>> mux_to_users;
dict<int, pool<struct MuxPort>> mux_to_users;
// Pure root muxes (outputs seen by non-muxes)
root_enable_muxes.resize(GetSize(mux2info));
// All root muxes (outputs seen by non-muxes or multiple muxes)
@ -188,8 +196,8 @@ struct OptMuxtreeWorker
for (auto &bi : bit2info) {
if (bi.mux_driver)
for (int j : bi.mux_users)
mux_to_users[*bi.mux_driver].insert(j);
for (auto muxport : bi.mux_users)
mux_to_users[*bi.mux_driver].insert(muxport);
if (!bi.seen_non_mux)
continue;
if (bi.mux_driver) {