mirrors/yosys
3
0
Fork 0
mirror of https://github.com/YosysHQ/yosys synced 2025-11-04 05:19:11 +00:00
Code Activity

opt_rmdff to optimise even in presence of enable signal, even removing

Browse source
This commit is contained in:
Eddie Hung 2019-05-24 18:30:51 -07:00
parent f0c6b73b72
commit 822d0b7789
1 changed files with 29 additions and 12 deletions
Download patch file Download diff file Expand all files Collapse all files

41
passes/opt/opt_rmdff.cc
View file

@ -338,15 +338,6 @@ bool handle_dff(RTLIL::Module *mod, RTLIL::Cell *dff)
val_init.bits.push_back(bit.wire == NULL ? bit.data : RTLIL::State::Sx);
}
if (sig_e.size()) {
if (!sig_e.is_fully_const())
return false;
if (sig_e != val_ep) {
mod->connect(sig_q, val_init);
goto delete_dff;
}
}
if (dff->type.in("$ff", "$dff") && mux_drivers.has(sig_d)) {
std::set<RTLIL::Cell*> muxes;
mux_drivers.find(sig_d, muxes);
@ -392,9 +383,11 @@ bool handle_dff(RTLIL::Module *mod, RTLIL::Cell *dff)
// If D is fully constant and (i) no reset signal
// (ii) reset value is same as constant D
// and (a) has initial value
// and (a) has no initial value
// (b) initial value same as constant D
if (sig_d.is_fully_const() && (!sig_r.size() || val_rv == sig_d.as_const()) && (!has_init || val_init == sig_d.as_const())) {
// and (1) has no enable signal
// (2) enable is always active
if (sig_d.is_fully_const() && (!sig_r.size() || val_rv == sig_d.as_const()) && (!has_init || val_init == sig_d.as_const()) && (!sig_e.size() || (sig_d.is_fully_undef() && !has_init))) {
// Q is permanently D
mod->connect(sig_q, sig_d);
goto delete_dff;
@ -415,7 +408,7 @@ bool handle_dff(RTLIL::Module *mod, RTLIL::Cell *dff)
// If reset signal is present, and is fully constant
if (!sig_r.empty() && sig_r.is_fully_const())
{
// If reset value is permanently enable or if reset is undefined
// If reset value is permanently active or if reset is undefined
if (sig_r == val_rp || sig_r.is_fully_undef()) {
// Q is permanently reset value
mod->connect(sig_q, val_rv);
@ -437,6 +430,30 @@ bool handle_dff(RTLIL::Module *mod, RTLIL::Cell *dff)
dff->unsetPort("\\R");
}
// If enable signal is present, and is fully constant
if (!sig_e.empty() && sig_e.is_fully_const())
{
// If enable value is permanently inactive
if (sig_e != val_ep) {
// Q is permanently initial value
mod->connect(sig_q, val_init);
goto delete_dff;
}
log("Removing unused enable from %s (%s) from module %s.\n", log_id(dff), log_id(dff->type), log_id(mod));
if (dff->type == "$dffe") {
dff->type = "$dff";
dff->unsetPort("\\EN");
dff->unsetParam("\\EN_POLARITY");
return true;
}
log_assert(dff->type.substr(0,7) == "$_DFFE_");
dff->type = stringf("$_DFF_%c_", + dff->type[7]);
dff->unsetPort("\\E");
}
return false;
delete_dff: