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Refactor and generalize the comparision optimization 

Generalizes the optimization to:
a < C,
a >= C,
C > a,
C <= a
This commit is contained in:
C-Elegans 2017-01-30 17:52:16 -05:00
parent 2fa0fd4a37
commit a94c3694d7
1 changed files with 42 additions and 22 deletions
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64
passes/opt/opt_expr.cc
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@ -258,6 +258,8 @@ bool is_one_or_minus_one(const Const &value, bool is_signed, bool &is_negative)
return last_bit_one; return last_bit_one;
} }
//if the signal has only one bit set, return the index of that bit.
//otherwise return -1
int get_onehot_bit_index(RTLIL::SigSpec signal){ int get_onehot_bit_index(RTLIL::SigSpec signal){
if(!signal.is_fully_const()) if(!signal.is_fully_const())
return -1; return -1;
@ -1187,32 +1189,50 @@ void replace_const_cells(RTLIL::Design *design, RTLIL::Module *module, bool cons
} }
} }
//replace a <0 or a >=0 with the top bit of a //replace a <0 or a >=0 with the top bit of a
if(do_fine && (cell->type == "$lt" || cell->type == "$ge")) if(do_fine && (cell->type == "$lt" || cell->type == "$ge" || cell->type == "$gt" || cell->type == "$le"))
{ {
bool is_lt = cell->type == "$lt" ? 1 : 0; bool is_lt = false; //used to decide whether the signal needs to be negated
RTLIL::SigSpec a = cell->getPort("\\A"); RTLIL::SigSpec sigVar; //references the variable signal in the comparison
RTLIL::SigSpec b = cell->getPort("\\B"); RTLIL::SigSpec sigConst; //references the constant signal in the comparison
int a_width = cell->parameters["\\A_WIDTH"].as_int(); //note that this signal must be constant for the optimization
//to take place, but it is not checked beforehand.
//If new passes are added, this signal must be checked for const-ness
int width; //width of the variable port
bool var_signed;
if(cell->type == "$lt" || cell->type == "$ge"){
is_lt = cell->type == "$lt" ? 1 : 0;
sigVar = cell->getPort("\\A");
sigConst = cell->getPort("\\B");
width = cell->parameters["\\A_WIDTH"].as_int();
var_signed = cell->parameters["\\A_SIGNED"].as_bool();
}
if(cell->type == "$gt" || cell->type == "$le"){
is_lt = cell->type == "$gt" ? 1 : 0;
sigVar = cell->getPort("\\B");
sigConst = cell->getPort("\\A");
width = cell->parameters["\\B_WIDTH"].as_int();
var_signed = cell->parameters["\\B_SIGNED"].as_bool();
}
//replace a(signed) < 0 with the high bit of a //replace a(signed) < 0 with the high bit of a
if(b.is_fully_const() && b.is_fully_zero() && cell->parameters["\\A_SIGNED"].as_bool() == true){ if(sigConst.is_fully_const() && sigConst.is_fully_zero() && var_signed == true){
RTLIL::SigSpec a_prime(RTLIL::State::S0, cell->parameters["\\Y_WIDTH"].as_int()); RTLIL::SigSpec a_prime(RTLIL::State::S0, cell->parameters["\\Y_WIDTH"].as_int());
a_prime[0] = a[a_width-1]; a_prime[0] = sigVar[width-1];
if(is_lt){ if(is_lt){
log("Optimizing a < 0 with a[%d]\n",a_width - 1); log("Optimizing a < 0 with a[%d]\n",width - 1);
module->connect(cell->getPort("\\Y"), a_prime); module->connect(cell->getPort("\\Y"), a_prime);
module->remove(cell); module->remove(cell);
} }
else{ else{
log("Optimizing a >= 0 with ~a[%d]\n",a_width - 1); log("Optimizing a >= 0 with ~a[%d]\n",width - 1);
module->addNot("$not", a_prime, cell->getPort("\\Y")); module->addNot(NEW_ID, a_prime, cell->getPort("\\Y"));
module->remove(cell); module->remove(cell);
} }
did_something = true; did_something = true;
goto next_cell; goto next_cell;
} }
else if(b.is_fully_const() && b.is_fully_def() && cell->parameters["\\A_SIGNED"].as_bool() == false){ else if(sigConst.is_fully_const() && sigConst.is_fully_def() && var_signed == false){
int b_bit_set = get_onehot_bit_index(b); int const_bit_set = get_onehot_bit_index(sigConst);
if(b.is_fully_zero()){ if(sigConst.is_fully_zero()){
RTLIL::SigSpec a_prime(RTLIL::State::S0,1); RTLIL::SigSpec a_prime(RTLIL::State::S0,1);
if(is_lt){ if(is_lt){
log("replacing a(unsigned) < 0 with constant false\n"); log("replacing a(unsigned) < 0 with constant false\n");
@ -1228,19 +1248,19 @@ void replace_const_cells(RTLIL::Design *design, RTLIL::Module *module, bool cons
goto next_cell; goto next_cell;
} }
else if(b_bit_set >= 0){ //if b has only 1 bit set else if(const_bit_set >= 0){ //if b has only 1 bit set
int bit_set = b_bit_set; int bit_set = const_bit_set;
RTLIL::SigSpec a_prime(RTLIL::State::S0,a_width-bit_set); RTLIL::SigSpec a_prime(RTLIL::State::S0,width-bit_set);
for(int i = bit_set; i < a_width; i++){ for(int i = bit_set; i < width; i++){
a_prime[i-bit_set] = a[i]; a_prime[i-bit_set] = sigVar[i];
} }
if(is_lt){ if(is_lt){
log("replacing a < %d with !a[%d:%d]\n",b.as_int(false),a_width-1,bit_set); log("replacing a < %d with !a[%d:%d]\n",sigConst.as_int(false),width-1,bit_set);
module->addLogicNot("$logic_not", a_prime,cell->getPort("\\Y")); module->addLogicNot(NEW_ID, a_prime,cell->getPort("\\Y"));
} }
else{ else{
log("replacing a >= %d with |a[%d:%d]\n",b.as_int(false),a_width-1,bit_set); log("replacing a >= %d with |a[%d:%d]\n",sigConst.as_int(false),width-1,bit_set);
module->addReduceOr("$reduce_or", a_prime,cell->getPort("\\Y")); module->addReduceOr(NEW_ID, a_prime,cell->getPort("\\Y"));
} }
module->remove(cell); module->remove(cell);
did_something = true; did_something = true;