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Fix errors in constant propagation. 

Ensure undriven, multiply-driven, and forced nets are correctly handled
by the constant propagation optimisation pass.
This commit is contained in:
Martin Whitaker 2013-10-26 01:07:21 +01:00
parent 1814c24a90
commit d291e2b23d
5 changed files with 100 additions and 160 deletions
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7
cprop.cc
View File

@ -1,5 +1,5 @@
/*
* Copyright (c) 1998-2010,2012 Stephen Williams (steve@icarus.com)
* Copyright (c) 1998-2013 Stephen Williams (steve@icarus.com)
*
* This source code is free software; you can redistribute it
* and/or modify it in source code form under the terms of the GNU
@ -163,11 +163,6 @@ void cprop_functor::lpm_mux(Design*des, NetMux*obj)
if (! sel_nex->drivers_constant())
return;
// If the select input is assigned or forced, then again there
// is nothing we can do here.
if (sel_nex->assign_lval())
return;
// If the constant select is 'bz or 'bx, then give up.
verinum::V sel_val = sel_nex->driven_value();
if (sel_val == verinum::Vz || sel_val == verinum::Vx)

130
link_const.cc
View File

@ -1,5 +1,5 @@
/*
* Copyright (c) 2000-2012 Stephen Williams (steve@icarus.com)
* Copyright (c) 2000-2013 Stephen Williams (steve@icarus.com)
*
* This source code is free software; you can redistribute it
* and/or modify it in source code form under the terms of the GNU
@ -25,8 +25,7 @@
/*
* Scan the link for drivers. If there are only constant drivers, then
* the nexus has a known constant value. If there is a supply net,
* then the nexus again has a known constant value.
* the nexus has a known constant value.
*/
bool Nexus::drivers_constant() const
{
@ -35,15 +34,23 @@ bool Nexus::drivers_constant() const
if (driven_ != NO_GUESS)
return true;
unsigned constant_drivers = 0;
for (const Link*cur = first_nlink() ; cur ; cur = cur->next_nlink()) {
Link::DIR cur_dir;
cur_dir = cur->get_dir();
/* A target of a procedural assign or force statement
can't be treated as constant. */
const NetNet*sig = dynamic_cast<const NetNet*>(cur->get_obj());
if (sig && (sig->peek_lref() > 0)) {
driven_ = VAR;
return false;
}
Link::DIR cur_dir = cur->get_dir();
if (cur_dir == Link::INPUT)
continue;
/* If this is an input or inout port of a root module,
then the is probably not a constant value. I
then this is probably not a constant value. I
certainly don't know what the value is, anyhow. This
can happen in cases like this:
@ -56,16 +63,9 @@ bool Nexus::drivers_constant() const
outside world. */
if (cur_dir == Link::PASSIVE) {
const NetNet*sig;
const NetPins*obj = cur->get_obj();
const NetObj*as_obj = dynamic_cast<const NetObj*>(obj);
if (as_obj == 0 || as_obj->scope()->parent() != 0)
if (sig == 0 || sig->scope()->parent() != 0)
continue;
sig = dynamic_cast<const NetNet*>(cur->get_obj());
assert(sig);
if (sig->port_type() == NetNet::NOT_A_PORT)
continue;
@ -74,19 +74,22 @@ bool Nexus::drivers_constant() const
driven_ = VAR;
return false;
}
/* If there is a supply net, then this nexus will have a
constant value independent of any drivers. */
if (const NetNet*s = dynamic_cast<const NetNet*>(cur->get_obj()))
switch (s->type()) {
/* If there is an implicit pullup/pulldown on a net,
count it as a constant driver. */
if (sig)
switch (sig->type()) {
case NetNet::SUPPLY0:
case NetNet::TRI0:
constant_drivers += 1;
driven_ = V0;
return true;
continue;
case NetNet::SUPPLY1:
case NetNet::TRI1:
constant_drivers += 1;
driven_ = V1;
return true;
continue;
default:
break;
}
@ -95,6 +98,18 @@ bool Nexus::drivers_constant() const
driven_ = VAR;
return false;
}
constant_drivers += 1;
}
/* If there is more than one constant driver for this nexus, we
would need to resolve the constant value, taking into account
the drive strengths. This is a lot of work for something that
will rarely occur, so for now leave the resolution to be done
at run time. */
if (constant_drivers > 1) {
driven_ = VAR;
return false;
}
return true;
@ -127,28 +142,25 @@ verinum::V Nexus::driven_value() const
const NetConst*obj;
const NetNet*sig;
if ((obj = dynamic_cast<const NetConst*>(cur->get_obj()))) {
// Multiple drivers are not currently supported.
ivl_assert(*obj, val == verinum::Vz);
val = obj->value(cur->get_pin());
} else if ((sig = dynamic_cast<const NetNet*>(cur->get_obj()))) {
// If we find an attached SUPPLY0/1, the we know
// from that what the driven value is. Stop now.
if (sig->type() == NetNet::SUPPLY0) {
driven_ = V0;
return verinum::V0;
}
if (sig->type() == NetNet::SUPPLY1) {
driven_ = V1;
return verinum::V1;
}
// If we find an attached TRI0/1, then this is a
// good guess for the driven value, but keep
// looking for something better.
if (sig->type() == NetNet::TRI0) {
// If we find an implicit pullup or pulldown on a
// net, this is a good guess for the driven value,
// but keep looking for other drivers.
if ((sig->type() == NetNet::SUPPLY0) ||
(sig->type() == NetNet::TRI0)) {
// Multiple drivers are not currently supported.
ivl_assert(*obj, val == verinum::Vz);
val = verinum::V0;
}
if (sig->type() == NetNet::TRI1) {
if ((sig->type() == NetNet::SUPPLY1) ||
(sig->type() == NetNet::TRI1)) {
// Multiple drivers are not currently supported.
ivl_assert(*obj, val == verinum::Vz);
val = verinum::V1;
}
}
@ -179,40 +191,44 @@ verinum Nexus::driven_vector() const
const Link*cur = list_;
verinum val;
unsigned width = 0;
for (cur = first_nlink() ; cur ; cur = cur->next_nlink()) {
const NetConst*obj;
const NetNet*sig;
if ((obj = dynamic_cast<const NetConst*>(cur->get_obj()))) {
// Multiple drivers are not currently supported.
ivl_assert(*obj, val.len() == 0);
ivl_assert(*obj, cur->get_pin() == 0);
val = obj->value();
width = val.len();
} else if ((sig = dynamic_cast<const NetNet*>(cur->get_obj()))) {
// If we find an attached SUPPLY0/1, the we know
// from that what the driven value is. Stop now.
if (sig->type() == NetNet::SUPPLY0) {
driven_ = V0;
return verinum(verinum::V0, sig->vector_width());
width = sig->vector_width();
// If we find an implicit pullup or pulldown on a
// net, this is a good guess for the driven value,
// but keep looking for other drivers.
if ((sig->type() == NetNet::SUPPLY0) ||
(sig->type() == NetNet::TRI0)) {
// Multiple drivers are not currently supported.
ivl_assert(*obj, val.len() == 0);
val = verinum(verinum::V0, width);
}
if ((sig->type() == NetNet::SUPPLY1) ||
(sig->type() == NetNet::TRI1)) {
// Multiple drivers are not currently supported.
ivl_assert(*obj, val.len() == 0);
val = verinum(verinum::V1, width);
}
}
if (sig->type() == NetNet::SUPPLY1) {
driven_ = V1;
return verinum(verinum::V1, sig->vector_width());
}
// If we find an attached TRI0/1, then this is a
// good guess for the driven value, but keep
// looking for something better.
if (sig->type() == NetNet::TRI0) {
val = verinum(verinum::V0, sig->vector_width());
}
if (sig->type() == NetNet::TRI1) {
val = verinum(verinum::V1, sig->vector_width());
}
}
}
// If we have a width but not a value, this must be an undriven net.
if (val.len() != width)
val = verinum(verinum::Vz, width);
return val;
}

9
net_link.cc
View File

@ -1,5 +1,5 @@
/*
* Copyright (c) 2000-2010 Stephen Williams (steve@icarus.com)
* Copyright (c) 2000-2013 Stephen Williams (steve@icarus.com)
*
* This source code is free software; you can redistribute it
* and/or modify it in source code form under the terms of the GNU
@ -311,16 +311,13 @@ bool Nexus::drivers_present() const
continue;
// Must be PASSIVE, so if it is some kind of net, see if
// it is the sort that might drive the nexus.
// it is the sort that might drive the nexus. Note that
// supply0/1 and tri0/1 nets are classified as OUTPUT.
const NetPins*obj;
unsigned pin;
cur->cur_link(obj, pin);
if (const NetNet*net = dynamic_cast<const NetNet*>(obj))
switch (net->type()) {
case NetNet::SUPPLY0:
case NetNet::SUPPLY1:
case NetNet::TRI0:
case NetNet::TRI1:
case NetNet::WAND:
case NetNet::WOR:
case NetNet::TRIAND:

111
netlist.cc
View File

@ -479,8 +479,23 @@ PortType::Enum PortType::merged( Enum lhs, Enum rhs )
return PINOUT;
}
void NetNet::initialize_dir_(Link::DIR dir)
void NetNet::initialize_dir_()
{
Link::DIR dir = Link::PASSIVE;
switch (type_) {
case REG:
case IMPLICIT_REG:
case SUPPLY0:
case SUPPLY1:
case TRI0:
case TRI1:
dir = Link::OUTPUT;
break;
default:
break;
}
if (pins_are_virtual()) {
if (0) cerr << "NetNet setting Link default dir" << endl;
set_default_dir(dir);
@ -564,24 +579,7 @@ NetNet::NetNet(NetScope*s, perm_string n, Type t,
ivl_assert(*this, 0);
}
Link::DIR dir = Link::PASSIVE;
switch (t) {
case REG:
case IMPLICIT_REG:
dir = Link::OUTPUT;
break;
case SUPPLY0:
dir = Link::OUTPUT;
break;
case SUPPLY1:
dir = Link::OUTPUT;
break;
default:
break;
}
initialize_dir_(dir);
initialize_dir_();
s->add_signal(this);
}
@ -600,24 +598,8 @@ NetNet::NetNet(NetScope*s, perm_string n, Type t, netstruct_t*ty)
{
//XXXX packed_dims_.push_back(netrange_t(calculate_count(ty)-1, 0));
calculate_slice_widths_from_packed_dims_();
Link::DIR dir = Link::PASSIVE;
switch (t) {
case REG:
case IMPLICIT_REG:
dir = Link::OUTPUT;
break;
case SUPPLY0:
dir = Link::OUTPUT;
break;
case SUPPLY1:
dir = Link::OUTPUT;
break;
default:
break;
}
initialize_dir_(dir);
initialize_dir_();
s->add_signal(this);
}
@ -629,24 +611,7 @@ NetNet::NetNet(NetScope*s, perm_string n, Type t, netdarray_t*ty)
discipline_(0),
eref_count_(0), lref_count_(0)
{
Link::DIR dir = Link::PASSIVE;
switch (t) {
case REG:
case IMPLICIT_REG:
dir = Link::OUTPUT;
break;
case SUPPLY0:
dir = Link::OUTPUT;
break;
case SUPPLY1:
dir = Link::OUTPUT;
break;
default:
break;
}
initialize_dir_(dir);
initialize_dir_();
s->add_signal(this);
}
@ -659,24 +624,8 @@ NetNet::NetNet(NetScope*s, perm_string n, Type t, netvector_t*ty)
eref_count_(0), lref_count_(0)
{
calculate_slice_widths_from_packed_dims_();
Link::DIR dir = Link::PASSIVE;
switch (t) {
case REG:
case IMPLICIT_REG:
dir = Link::OUTPUT;
break;
case SUPPLY0:
dir = Link::OUTPUT;
break;
case SUPPLY1:
dir = Link::OUTPUT;
break;
default:
break;
}
initialize_dir_(dir);
initialize_dir_();
s->add_signal(this);
}
@ -712,27 +661,9 @@ void NetNet::type(NetNet::Type t)
if (type_ == t)
return;
Link::DIR dir = Link::PASSIVE;
switch (t) {
case REG:
case IMPLICIT_REG:
dir = Link::OUTPUT;
break;
case SUPPLY0:
dir = Link::OUTPUT;
break;
case SUPPLY1:
dir = Link::OUTPUT;
break;
default:
break;
}
type_ = t;
for (unsigned idx = 0 ; idx < pin_count() ; idx += 1) {
pin(idx).set_dir(dir);
}
initialize_dir_();
}

7
netlist.h
View File

@ -581,9 +581,10 @@ class NetDelaySrc : public NetObj {
*
* NetNet objects are located by searching NetScope objects.
*
* The pins of a NetNet object are PASSIVE: they do not drive
* The pins of a NetNet object are usually PASSIVE: they do not drive
* anything and they are not a data sink, per se. The pins follow the
* values on the nexus.
* values on the nexus. The exceptions are reg, trireg, tri0, tri1,
* supply0, and supply1 objects, whose pins are classed as OUTPUT.
*/
class PortType
@ -746,7 +747,7 @@ class NetNet : public NetObj, public PortType {
virtual void dump_net(ostream&, unsigned) const;
private:
void initialize_dir_(Link::DIR dir);
void initialize_dir_();
private:
Type type_ : 5;