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extract_counter: Added optimizations to remove unused high-order bits

This commit is contained in:
Andrew Zonenberg 2017-08-30 18:14:22 -07:00
parent 634f18be96
commit ed1e3ed39b
1 changed files with 34 additions and 16 deletions
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50
passes/techmap/extract_counter.cc
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@ -387,22 +387,6 @@ void counter_worker(
//Get new cell name
string countname = string("$COUNTx$") + log_id(extract.rwire->name.str());
//Log it
total_counters ++;
string reset_type = "non-resettable";
if(extract.has_reset)
{
//TODO: support other kind of reset
reset_type = "async resettable";
}
log(" Found %d-bit %s down counter %s (counting from %d) for register %s declared at %s\n",
extract.width,
reset_type.c_str(),
countname.c_str(),
extract.count_value,
log_id(extract.rwire->name),
count_reg_src.c_str());
//Wipe all of the old connections to the ALU
cell->unsetPort("\\A");
cell->unsetPort("\\B");
@ -466,6 +450,40 @@ void counter_worker(
cells_to_remove.insert(extract.count_reg);
cells_to_remove.insert(extract.underflow_inv);
//Log it
total_counters ++;
string reset_type = "non-resettable";
if(extract.has_reset)
{
//TODO: support other kind of reset
reset_type = "async resettable";
}
log(" Found %d-bit %s down counter %s (counting from %d) for register %s declared at %s\n",
extract.width,
reset_type.c_str(),
countname.c_str(),
extract.count_value,
log_id(extract.rwire->name),
count_reg_src.c_str());
//Optimize the counter
//If we have no parallel output, and we have redundant bits, shrink us
if(extract.pouts.empty())
{
//TODO: Need to update this when we add support for counters with nonzero reset values
//to make sure the reset value fits in our bit space too
//Optimize it
int newbits = ceil(log2(extract.count_value));
if(extract.width != newbits)
{
cell->setParam("\\WIDTH", RTLIL::Const(newbits));
log(" Optimizing out %d unused high-order bits (new width is %d)\n",
extract.width - newbits,
newbits);
}
}
//Finally, rename the cell
cells_to_rename.insert(pair<Cell*, string>(cell, countname));
}