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Constant propagation for compare ==.

This commit is contained in:
steve 2001-02-16 03:27:31 +00:00
parent d3bff8a451
commit 59b69c6dd1
1 changed files with 110 additions and 1 deletions
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111
cprop.cc
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@ -17,7 +17,7 @@
* Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA
*/
#if !defined(WINNT) && !defined(macintosh)
#ident "$Id: cprop.cc,v 1.24 2001/02/10 04:50:54 steve Exp $"
#ident "$Id: cprop.cc,v 1.25 2001/02/16 03:27:31 steve Exp $"
#endif
# include "netlist.h"
@ -39,6 +39,8 @@ struct cprop_functor : public functor_t {
unsigned count;
virtual void lpm_add_sub(Design*des, NetAddSub*obj);
virtual void lpm_compare(Design*des, NetCompare*obj);
virtual void lpm_compare_eq_(Design*des, NetCompare*obj);
virtual void lpm_ff(Design*des, NetFF*obj);
virtual void lpm_logic(Design*des, NetLogic*obj);
virtual void lpm_mux(Design*des, NetMux*obj);
@ -128,6 +130,110 @@ void cprop_functor::lpm_add_sub(Design*des, NetAddSub*obj)
}
void cprop_functor::lpm_compare(Design*des, NetCompare*obj)
{
if (obj->pin_AEB().is_linked()) {
assert( ! obj->pin_AGB().is_linked() );
assert( ! obj->pin_AGEB().is_linked() );
assert( ! obj->pin_ALB().is_linked() );
assert( ! obj->pin_ALEB().is_linked() );
assert( ! obj->pin_AGB().is_linked() );
assert( ! obj->pin_ANEB().is_linked() );
lpm_compare_eq_(des, obj);
return;
}
}
void cprop_functor::lpm_compare_eq_(Design*des, NetCompare*obj)
{
/* First, look for the case where constant bits on matching A
and B inputs are different. This this is so, the device can
be completely eliminated and replaced with a constant 0. */
for (unsigned idx = 0 ; idx < obj->width() ; idx += 1) {
if (! link_drivers_constant(obj->pin_DataA(idx)))
continue;
if (! link_drivers_constant(obj->pin_DataB(idx)))
continue;
if (driven_value(obj->pin_DataA(idx)) ==
driven_value(obj->pin_DataB(idx)))
continue;
NetConst*zero = new NetConst(obj->name(), verinum::V0);
connect(zero->pin(0), obj->pin_AEB());
delete obj;
des->add_node(zero);
count += 1;
return;
}
/* Still may need the gate. Run through the inputs again, and
look for pairs of constants. Those inputs can be removed. */
unsigned top = obj->width();
for (unsigned idx = 0 ; idx < top ; ) {
if (! link_drivers_constant(obj->pin_DataA(idx))) {
idx += 1;
continue;
}
if (! link_drivers_constant(obj->pin_DataB(idx))) {
idx += 1;
continue;
}
obj->pin_DataA(idx).unlink();
obj->pin_DataB(idx).unlink();
top -= 1;
for (unsigned jj = idx ; jj < top ; jj += 1) {
connect(obj->pin_DataA(jj), obj->pin_DataA(jj+1));
connect(obj->pin_DataB(jj), obj->pin_DataB(jj+1));
obj->pin_DataA(jj+1).unlink();
obj->pin_DataB(jj+1).unlink();
}
}
/* If we wound up disconnecting all the inputs, then remove
the device and replace it with a constant. */
if (top == 0) {
NetConst*one = new NetConst(obj->name(), verinum::V1);
connect(one->pin(0), obj->pin_AEB());
delete obj;
des->add_node(one);
count += 1;
return;
}
/* If there is only one bit left, then replace the comparator
with a simple XOR gate. */
if (top == 1) {
NetLogic*tmp = new NetLogic(obj->scope(), obj->name(), 3,
NetLogic::XOR);
connect(tmp->pin(0), obj->pin_AEB());
connect(tmp->pin(1), obj->pin_DataA(0));
connect(tmp->pin(2), obj->pin_DataB(0));
delete obj;
des->add_node(tmp);
count += 1;
return;
}
if (top == obj->width())
return;
NetCompare*tmp = new NetCompare(obj->name(), top);
connect(tmp->pin_AEB(), obj->pin_AEB());
for (unsigned idx = 0 ; idx < top ; idx += 1) {
connect(tmp->pin_DataA(idx), obj->pin_DataA(idx));
connect(tmp->pin_DataB(idx), obj->pin_DataB(idx));
}
delete obj;
des->add_node(tmp);
count += 1;
}
void cprop_functor::lpm_ff(Design*des, NetFF*obj)
{
// Look for and count unlinked FF outputs. Note that if the
@ -826,6 +932,9 @@ void cprop(Design*des)
/*
* $Log: cprop.cc,v $
* Revision 1.25 2001/02/16 03:27:31 steve
* Constant propagation for compare ==.
*
* Revision 1.24 2001/02/10 04:50:54 steve
* Catch constants driving root module ports. (PR#130)
*