// Given an expression for a shift amount, and a maximum width,
// generate the FIRRTL expression for equivalent dynamic shift taking into account FIRRTL shift semantics.
- std::string gen_dshl(const string b_expr, const int b_padded_width)
+ std::string gen_dshl(const string b_expr, const int b_width)
{
string result = b_expr;
- if (b_padded_width >= FIRRTL_MAX_DSH_WIDTH_ERROR) {
+ if (b_width >= FIRRTL_MAX_DSH_WIDTH_ERROR) {
int max_shift_width_bits = FIRRTL_MAX_DSH_WIDTH_ERROR - 1;
string max_shift_string = stringf("UInt<%d>(%d)", max_shift_width_bits, (1<<max_shift_width_bits) - 1);
// Deal with the difference in semantics between FIRRTL and verilog
for (auto cell : module->cells())
{
- bool extract_y_bits = false; // Assume no extraction of final bits will be required.
+ static Const ndef(0, 0);
+
// Is this cell is a module instance?
if (cell->type[0] != '$')
{
process_instance(cell, wire_exprs);
continue;
}
+ // Not a module instance. Set up cell properties
+ bool extract_y_bits = false; // Assume no extraction of final bits will be required.
+ int a_width = cell->parameters.at("\\A_WIDTH", ndef).as_int(); // The width of "A"
+ int b_width = cell->parameters.at("\\B_WIDTH", ndef).as_int(); // The width of "A"
+ const int y_width = cell->parameters.at("\\Y_WIDTH", ndef).as_int(); // The width of the result
+ const bool a_signed = cell->parameters.at("\\A_SIGNED", ndef).as_bool();
+ const bool b_signed = cell->parameters.at("\\B_SIGNED", ndef).as_bool();
+ bool firrtl_is_signed = a_signed; // The result is signed (subsequent code may change this).
+ int firrtl_width = 0;
+ string primop;
+ bool always_uint = false;
+ string y_id = make_id(cell->name);
+
if (cell->type.in("$not", "$logic_not", "$neg", "$reduce_and", "$reduce_or", "$reduce_xor", "$reduce_bool", "$reduce_xnor"))
{
- string y_id = make_id(cell->name);
- bool is_signed = cell->parameters.at("\\A_SIGNED").as_bool();
- int y_width = cell->parameters.at("\\Y_WIDTH").as_int();
string a_expr = make_expr(cell->getPort("\\A"));
wire_decls.push_back(stringf(" wire %s: UInt<%d>\n", y_id.c_str(), y_width));
- if (cell->parameters.at("\\A_SIGNED").as_bool()) {
+ if (a_signed) {
a_expr = "asSInt(" + a_expr + ")";
}
a_expr = stringf("pad(%s, %d)", a_expr.c_str(), y_width);
}
- string primop;
- bool always_uint = false;
+ // Assume the FIRRTL width is a single bit.
+ firrtl_width = 1;
if (cell->type == "$not") primop = "not";
else if (cell->type == "$neg") {
primop = "neg";
- is_signed = true; // Result of "neg" is signed (an SInt).
+ firrtl_is_signed = true; // Result of "neg" is signed (an SInt).
+ firrtl_width = a_width;
} else if (cell->type == "$logic_not") {
primop = "eq";
a_expr = stringf("%s, UInt(0)", a_expr.c_str());
else if (cell->type == "$reduce_bool") {
primop = "neq";
// Use the sign of the a_expr and its width as the type (UInt/SInt) and width of the comparand.
- bool a_signed = cell->parameters.at("\\A_SIGNED").as_bool();
- int a_width = cell->parameters.at("\\A_WIDTH").as_int();
a_expr = stringf("%s, %cInt<%d>(0)", a_expr.c_str(), a_signed ? 'S' : 'U', a_width);
}
string expr = stringf("%s(%s)", primop.c_str(), a_expr.c_str());
- if ((is_signed && !always_uint))
+ if ((firrtl_is_signed && !always_uint))
expr = stringf("asUInt(%s)", expr.c_str());
cell_exprs.push_back(stringf(" %s <= %s\n", y_id.c_str(), expr.c_str()));
continue;
}
- if (cell->type.in("$add", "$sub", "$mul", "$div", "$mod", "$xor", "$and", "$or", "$eq", "$eqx",
+ if (cell->type.in("$add", "$sub", "$mul", "$div", "$mod", "$xor", "$xnor", "$and", "$or", "$eq", "$eqx",
"$gt", "$ge", "$lt", "$le", "$ne", "$nex", "$shr", "$sshr", "$sshl", "$shl",
- "$logic_and", "$logic_or"))
+ "$logic_and", "$logic_or", "$pow"))
{
- string y_id = make_id(cell->name);
- bool is_signed = cell->parameters.at("\\A_SIGNED").as_bool();
- int y_width = cell->parameters.at("\\Y_WIDTH").as_int();
string a_expr = make_expr(cell->getPort("\\A"));
string b_expr = make_expr(cell->getPort("\\B"));
- int b_padded_width = cell->parameters.at("\\B_WIDTH").as_int();
wire_decls.push_back(stringf(" wire %s: UInt<%d>\n", y_id.c_str(), y_width));
- if (cell->parameters.at("\\A_SIGNED").as_bool()) {
+ if (a_signed) {
a_expr = "asSInt(" + a_expr + ")";
- }
- // Shift amount is always unsigned, and needn't be padded to result width.
- if (!cell->type.in("$shr", "$sshr", "$shl", "$sshl")) {
- if (cell->parameters.at("\\B_SIGNED").as_bool()) {
- b_expr = "asSInt(" + b_expr + ")";
+ // Expand the "A" operand to the result width
+ if (a_width < y_width) {
+ a_expr = stringf("pad(%s, %d)", a_expr.c_str(), y_width);
+ a_width = y_width;
}
- if (b_padded_width < y_width) {
- auto b_sig = cell->getPort("\\B");
- b_padded_width = y_width;
+ }
+ // Shift amount is always unsigned, and needn't be padded to result width,
+ // otherwise, we need to cast the b_expr appropriately
+ if (b_signed && !cell->type.in("$shr", "$sshr", "$shl", "$sshl", "$pow")) {
+ b_expr = "asSInt(" + b_expr + ")";
+ // Expand the "B" operand to the result width
+ if (b_width < y_width) {
+ b_expr = stringf("pad(%s, %d)", b_expr.c_str(), y_width);
+ b_width = y_width;
}
}
+ // For the arithmetic ops, expand operand widths to result widths befor performing the operation.
+ // This corresponds (according to iverilog) to what verilog compilers implement.
+ if (cell->type.in("$add", "$sub", "$mul", "$div", "$mod", "$xor", "$xnor", "$and", "$or"))
+ {
+ if (a_width < y_width) {
+ a_expr = stringf("pad(%s, %d)", a_expr.c_str(), y_width);
+ a_width = y_width;
+ }
+ if (b_width < y_width) {
+ b_expr = stringf("pad(%s, %d)", b_expr.c_str(), y_width);
+ b_width = y_width;
+ }
+ }
+ // Assume the FIRRTL width is the width of "A"
+ firrtl_width = a_width;
auto a_sig = cell->getPort("\\A");
- if (cell->parameters.at("\\A_SIGNED").as_bool() & (cell->type == "$shr")) {
- a_expr = "asUInt(" + a_expr + ")";
+ if (cell->type == "$add") {
+ primop = "add";
+ firrtl_is_signed = a_signed | b_signed;
+ firrtl_width = max(a_width, b_width);
+ } else if (cell->type == "$sub") {
+ primop = "sub";
+ firrtl_is_signed = true;
+ int a_widthInc = (!a_signed && b_signed) ? 2 : (a_signed && !b_signed) ? 1 : 0;
+ int b_widthInc = (a_signed && !b_signed) ? 2 : (!a_signed && b_signed) ? 1 : 0;
+ firrtl_width = max(a_width + a_widthInc, b_width + b_widthInc);
+ } else if (cell->type == "$mul") {
+ primop = "mul";
+ firrtl_is_signed = a_signed | b_signed;
+ firrtl_width = a_width + b_width;
+ } else if (cell->type == "$div") {
+ primop = "div";
+ firrtl_is_signed = a_signed | b_signed;
+ firrtl_width = a_width;
+ } else if (cell->type == "$mod") {
+ primop = "rem";
+ firrtl_width = min(a_width, b_width);
+ } else if (cell->type == "$and") {
+ primop = "and";
+ always_uint = true;
+ firrtl_width = max(a_width, b_width);
}
-
- string primop;
- bool always_uint = false;
- if (cell->type == "$add") primop = "add";
- else if (cell->type == "$sub") primop = "sub";
- else if (cell->type == "$mul") primop = "mul";
- else if (cell->type == "$div") primop = "div";
- else if (cell->type == "$mod") primop = "rem";
- else if (cell->type == "$and") {
- primop = "and";
- always_uint = true;
- }
else if (cell->type == "$or" ) {
- primop = "or";
- always_uint = true;
- }
+ primop = "or";
+ always_uint = true;
+ firrtl_width = max(a_width, b_width);
+ }
else if (cell->type == "$xor") {
- primop = "xor";
- always_uint = true;
- }
+ primop = "xor";
+ always_uint = true;
+ firrtl_width = max(a_width, b_width);
+ }
+ else if (cell->type == "$xnor") {
+ primop = "xnor";
+ always_uint = true;
+ firrtl_width = max(a_width, b_width);
+ }
else if ((cell->type == "$eq") | (cell->type == "$eqx")) {
- primop = "eq";
- always_uint = true;
- }
+ primop = "eq";
+ always_uint = true;
+ firrtl_width = 1;
+ }
else if ((cell->type == "$ne") | (cell->type == "$nex")) {
- primop = "neq";
- always_uint = true;
- }
+ primop = "neq";
+ always_uint = true;
+ firrtl_width = 1;
+ }
else if (cell->type == "$gt") {
- primop = "gt";
- always_uint = true;
- }
+ primop = "gt";
+ always_uint = true;
+ firrtl_width = 1;
+ }
else if (cell->type == "$ge") {
- primop = "geq";
- always_uint = true;
- }
+ primop = "geq";
+ always_uint = true;
+ firrtl_width = 1;
+ }
else if (cell->type == "$lt") {
- primop = "lt";
- always_uint = true;
- }
+ primop = "lt";
+ always_uint = true;
+ firrtl_width = 1;
+ }
else if (cell->type == "$le") {
- primop = "leq";
- always_uint = true;
- }
+ primop = "leq";
+ always_uint = true;
+ firrtl_width = 1;
+ }
else if ((cell->type == "$shl") | (cell->type == "$sshl")) {
// FIRRTL will widen the result (y) by the amount of the shift.
// We'll need to offset this by extracting the un-widened portion as Verilog would do.
auto b_sig = cell->getPort("\\B");
if (b_sig.is_fully_const()) {
primop = "shl";
- b_expr = std::to_string(b_sig.as_int());
+ int shift_amount = b_sig.as_int();
+ b_expr = std::to_string(shift_amount);
+ firrtl_width = a_width + shift_amount;
} else {
primop = "dshl";
// Convert from FIRRTL left shift semantics.
- b_expr = gen_dshl(b_expr, b_padded_width);
+ b_expr = gen_dshl(b_expr, b_width);
+ firrtl_width = a_width + (1 << b_width) - 1;
}
}
else if ((cell->type == "$shr") | (cell->type == "$sshr")) {
auto b_sig = cell->getPort("\\B");
if (b_sig.is_fully_const()) {
primop = "shr";
- b_expr = std::to_string(b_sig.as_int());
+ int shift_amount = b_sig.as_int();
+ b_expr = std::to_string(shift_amount);
+ firrtl_width = max(1, a_width - shift_amount);
} else {
primop = "dshr";
+ firrtl_width = a_width;
+ }
+ // We'll need to do some special fixups if the source (and thus result) is signed.
+ if (firrtl_is_signed) {
+ // If this is a "logical" shift right, pretend the source is unsigned.
+ if (cell->type == "$shr") {
+ a_expr = "asUInt(" + a_expr + ")";
+ }
}
}
else if ((cell->type == "$logic_and")) {
- primop = "and";
- a_expr = "neq(" + a_expr + ", UInt(0))";
- b_expr = "neq(" + b_expr + ", UInt(0))";
- always_uint = true;
- }
+ primop = "and";
+ a_expr = "neq(" + a_expr + ", UInt(0))";
+ b_expr = "neq(" + b_expr + ", UInt(0))";
+ always_uint = true;
+ firrtl_width = 1;
+ }
else if ((cell->type == "$logic_or")) {
- primop = "or";
- a_expr = "neq(" + a_expr + ", UInt(0))";
- b_expr = "neq(" + b_expr + ", UInt(0))";
- always_uint = true;
- }
+ primop = "or";
+ a_expr = "neq(" + a_expr + ", UInt(0))";
+ b_expr = "neq(" + b_expr + ", UInt(0))";
+ always_uint = true;
+ firrtl_width = 1;
+ }
+ else if ((cell->type == "$pow")) {
+ if (a_sig.is_fully_const() && a_sig.as_int() == 2) {
+ // We'll convert this to a shift. To simplify things, change the a_expr to "1"
+ // so we can use b_expr directly as a shift amount.
+ // Only support 2 ** N (i.e., shift left)
+ // FIRRTL will widen the result (y) by the amount of the shift.
+ // We'll need to offset this by extracting the un-widened portion as Verilog would do.
+ a_expr = firrtl_is_signed ? "SInt(1)" : "UInt(1)";
+ extract_y_bits = true;
+ // Is the shift amount constant?
+ auto b_sig = cell->getPort("\\B");
+ if (b_sig.is_fully_const()) {
+ primop = "shl";
+ int shiftAmount = b_sig.as_int();
+ if (shiftAmount < 0) {
+ log_error("Negative power exponent - %d: %s.%s\n", shiftAmount, log_id(module), log_id(cell));
+ }
+ b_expr = std::to_string(shiftAmount);
+ firrtl_width = a_width + shiftAmount;
+ } else {
+ primop = "dshl";
+ // Convert from FIRRTL left shift semantics.
+ b_expr = gen_dshl(b_expr, b_width);
+ firrtl_width = a_width + (1 << b_width) - 1;
+ }
+ } else {
+ log_error("Non power 2: %s.%s\n", log_id(module), log_id(cell));
+ }
+ }
if (!cell->parameters.at("\\B_SIGNED").as_bool()) {
b_expr = "asUInt(" + b_expr + ")";
}
- string expr = stringf("%s(%s, %s)", primop.c_str(), a_expr.c_str(), b_expr.c_str());
+ string expr;
+ // Deal with $xnor == ~^ (not xor)
+ if (primop == "xnor") {
+ expr = stringf("not(xor(%s, %s))", a_expr.c_str(), b_expr.c_str());
+ } else {
+ expr = stringf("%s(%s, %s)", primop.c_str(), a_expr.c_str(), b_expr.c_str());
+ }
- // Deal with FIRRTL's "shift widens" semantics
+ // Deal with FIRRTL's "shift widens" semantics, or the need to widen the FIRRTL result.
+ // If the operation is signed, the FIRRTL width will be 1 one bit larger.
if (extract_y_bits) {
expr = stringf("bits(%s, %d, 0)", expr.c_str(), y_width - 1);
+ } else if (firrtl_is_signed && (firrtl_width + 1) < y_width) {
+ expr = stringf("pad(%s, %d)", expr.c_str(), y_width);
}
- if ((is_signed && !always_uint) || cell->type.in("$sub"))
+ if ((firrtl_is_signed && !always_uint))
expr = stringf("asUInt(%s)", expr.c_str());
cell_exprs.push_back(stringf(" %s <= %s\n", y_id.c_str(), expr.c_str()));
if (cell->type.in("$mux"))
{
- string y_id = make_id(cell->name);
int width = cell->parameters.at("\\WIDTH").as_int();
string a_expr = make_expr(cell->getPort("\\A"));
string b_expr = make_expr(cell->getPort("\\B"));
if (clkpol == false)
log_error("Negative edge clock on FF %s.%s.\n", log_id(module), log_id(cell));
- string q_id = make_id(cell->name);
int width = cell->parameters.at("\\WIDTH").as_int();
string expr = make_expr(cell->getPort("\\D"));
string clk_expr = "asClock(" + make_expr(cell->getPort("\\CLK")) + ")";
- wire_decls.push_back(stringf(" reg %s: UInt<%d>, %s\n", q_id.c_str(), width, clk_expr.c_str()));
+ wire_decls.push_back(stringf(" reg %s: UInt<%d>, %s\n", y_id.c_str(), width, clk_expr.c_str()));
- cell_exprs.push_back(stringf(" %s <= %s\n", q_id.c_str(), expr.c_str()));
- register_reverse_wire_map(q_id, cell->getPort("\\Q"));
+ cell_exprs.push_back(stringf(" %s <= %s\n", y_id.c_str(), expr.c_str()));
+ register_reverse_wire_map(y_id, cell->getPort("\\Q"));
continue;
}
// assign y = a[b +: y_width];
// We'll extract the correct bits as part of the primop.
- string y_id = make_id(cell->name);
- int y_width = cell->parameters.at("\\Y_WIDTH").as_int();
string a_expr = make_expr(cell->getPort("\\A"));
// Get the initial bit selector
string b_expr = make_expr(cell->getPort("\\B"));
// assign y = a >> b;
// where b may be negative
- string y_id = make_id(cell->name);
- int y_width = cell->parameters.at("\\Y_WIDTH").as_int();
string a_expr = make_expr(cell->getPort("\\A"));
string b_expr = make_expr(cell->getPort("\\B"));
auto b_string = b_expr.c_str();
- int b_padded_width = cell->parameters.at("\\B_WIDTH").as_int();
string expr;
wire_decls.push_back(stringf(" wire %s: UInt<%d>\n", y_id.c_str(), y_width));
if (cell->getParam("\\B_SIGNED").as_bool()) {
// We generate a left or right shift based on the sign of b.
- std::string dshl = stringf("bits(dshl(%s, %s), 0, %d)", a_expr.c_str(), gen_dshl(b_expr, b_padded_width).c_str(), y_width);
+ std::string dshl = stringf("bits(dshl(%s, %s), 0, %d)", a_expr.c_str(), gen_dshl(b_expr, b_width).c_str(), y_width);
std::string dshr = stringf("dshr(%s, %s)", a_expr.c_str(), b_string);
expr = stringf("mux(%s < 0, %s, %s)",
b_string,
register_reverse_wire_map(y_id, cell->getPort("\\Y"));
continue;
}
+ if (cell->type == "$pos") {
+ // assign y = a;
+// printCell(cell);
+ string a_expr = make_expr(cell->getPort("\\A"));
+ // Verilog appears to treat the result as signed, so if the result is wider than "A",
+ // we need to pad.
+ if (a_width < y_width) {
+ a_expr = stringf("pad(%s, %d)", a_expr.c_str(), y_width);
+ }
+ wire_decls.push_back(stringf(" wire %s: UInt<%d>\n", y_id.c_str(), y_width));
+ cell_exprs.push_back(stringf(" %s <= %s\n", y_id.c_str(), a_expr.c_str()));
+ register_reverse_wire_map(y_id, cell->getPort("\\Y"));
+ continue;
+ }
log_warning("Cell type not supported: %s (%s.%s)\n", log_id(cell->type), log_id(module), log_id(cell));
}
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