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package firrtl
package transforms
import firrtl.ir._
import firrtl.Mappers._
import firrtl.PrimOps._
import firrtl.WrappedExpression._
import scala.collection.mutable
object ReplaceTruncatingArithmetic {
/** Mapping from references to the [[Expression]]s that drive them */
type Netlist = mutable.HashMap[WrappedExpression, Expression]
private val SeqBIOne = Seq(BigInt(1))
/** Replaces truncating arithmetic in an Expression
*
* @param netlist a '''mutable''' HashMap mapping references to [[DefNode]]s to their connected
* [[Expression]]s. It is '''not''' mutated in this function
* @param expr the Expression being transformed
* @return Returns expr with truncating arithmetic replaced
*/
def onExpr(netlist: Netlist)(expr: Expression): Expression =
expr.map(onExpr(netlist)) match {
case orig @ DoPrim(Tail, Seq(e), SeqBIOne, tailtpe) =>
netlist.getOrElse(we(e), e) match {
case DoPrim(Add, args, cs, _) => DoPrim(Addw, args, cs, tailtpe)
case DoPrim(Sub, args, cs, _) => DoPrim(Subw, args, cs, tailtpe)
case _ => orig // Not a candidate
}
case other => other // Not a candidate
}
/** Replaces truncating arithmetic in a Statement
*
* @param netlist a '''mutable''' HashMap mapping references to [[DefNode]]s to their connected
* [[Expression]]s. This function '''will''' mutate it if stmt contains a [[DefNode]]
* @param stmt the Statement being searched for nodes and transformed
* @return Returns stmt with truncating arithmetic replaced
*/
def onStmt(netlist: Netlist)(stmt: Statement): Statement =
stmt.map(onStmt(netlist)).map(onExpr(netlist)) match {
case node @ DefNode(_, name, value) =>
netlist(we(WRef(name))) = value
node
case other => other
}
/** Replaces truncating arithmetic in a Module */
def onMod(mod: DefModule): DefModule = mod.map(onStmt(new Netlist))
}
/** Replaces non-expanding arithmetic
*
* In the case where the result of `add` or `sub` immediately throws away the expanded msb, this
* transform will replace the operation with a non-expanding operator `addw` or `subw`
* respectively.
*
* @note This replaces some FIRRTL primops with ops that are not actually legal FIRRTL. They are
* useful for emission to languages that support non-expanding arithmetic (like Verilog)
*/
class ReplaceTruncatingArithmetic extends Transform {
def inputForm = LowForm
def outputForm = LowForm
def execute(state: CircuitState): CircuitState = {
val modulesx = state.circuit.modules.map(ReplaceTruncatingArithmetic.onMod(_))
state.copy(circuit = state.circuit.copy(modules = modulesx))
}
}
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