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Add removing of redundant pairs of bits in ==, ===, !=, and !== to opt_expr

This commit is contained in:
Clifford Wolf 2017-08-25 16:02:15 +02:00
parent 86df0fb381
commit db6d78a186
1 changed files with 72 additions and 0 deletions
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72
passes/opt/opt_expr.cc
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@ -1252,6 +1252,78 @@ void replace_const_cells(RTLIL::Design *design, RTLIL::Module *module, bool cons
}
}
// remove redundant pairs of bits in ==, ===, !=, and !==
// replace cell with const driver if inputs can't be equal
if (do_fine && cell->type.in("$eq", "$ne", "$eqx", "$nex"))
{
pool<pair<SigBit, SigBit>> redundant_cache;
mfp<SigBit> contradiction_cache;
contradiction_cache.promote(State::S0);
contradiction_cache.promote(State::S1);
int a_width = cell->getParam("\\A_WIDTH").as_int();
int b_width = cell->getParam("\\B_WIDTH").as_int();
bool is_signed = cell->getParam("\\A_SIGNED").as_bool();
int width = is_signed ? std::min(a_width, b_width) : std::max(a_width, b_width);
SigSpec sig_a = cell->getPort("\\A");
SigSpec sig_b = cell->getPort("\\B");
int redundant_bits = 0;
for (int i = width-1; i >= 0; i--)
{
SigBit bit_a = i < a_width ? assign_map(sig_a[i]) : State::S0;
SigBit bit_b = i < b_width ? assign_map(sig_b[i]) : State::S0;
contradiction_cache.merge(bit_a, bit_b);
if (bit_b < bit_a)
std::swap(bit_a, bit_b);
pair<SigBit, SigBit> key(bit_a, bit_b);
if (redundant_cache.count(key)) {
if (i < a_width) sig_a.remove(i);
if (i < b_width) sig_b.remove(i);
redundant_bits++;
continue;
}
redundant_cache.insert(key);
}
if (contradiction_cache.find(State::S0) == contradiction_cache.find(State::S1))
{
SigSpec y_sig = cell->getPort("\\Y");
Const y_value(cell->type.in("$eq", "$eqx") ? 0 : 1, GetSize(y_sig));
log("Replacing cell `%s' in module `%s' with constant driver %s.\n",
log_id(cell), log_id(module), log_signal(y_value));
module->connect(y_sig, y_value);
module->remove(cell);
did_something = true;
goto next_cell;
}
if (redundant_bits)
{
log("Removed %d redundant input bits from %s cell `%s' in module `%s'.\n",
redundant_bits, log_id(cell->type), log_id(cell), log_id(module));
cell->setPort("\\A", sig_a);
cell->setPort("\\B", sig_b);
cell->setParam("\\A_WIDTH", GetSize(sig_a));
cell->setParam("\\B_WIDTH", GetSize(sig_b));
did_something = true;
goto next_cell;
}
}
// replace a<0 or a>=0 with the top bit of a
if (do_fine && (cell->type == "$lt" || cell->type == "$ge" || cell->type == "$gt" || cell->type == "$le"))
{