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package firrtl
package passes
import firrtl.ir._
import firrtl.PrimOps._
import firrtl.Mappers._
// Makes all implicit width extensions and truncations explicit
object PadWidths extends Pass {
def name = "Pad Widths"
private def width(t: Type): Int = bitWidth(t).toInt
private def width(e: Expression): Int = width(e.tpe)
// Returns an expression with the correct integer width
private def fixup(i: Int)(e: Expression) = {
def tx = e.tpe match {
case t: UIntType => UIntType(IntWidth(i))
case t: SIntType => SIntType(IntWidth(i))
// default case should never be reached
}
width(e) match {
case j if i > j => DoPrim(Pad, Seq(e), Seq(i), tx)
case j if i < j =>
val e2 = DoPrim(Bits, Seq(e), Seq(i - 1, 0), UIntType(IntWidth(i)))
// Bit Select always returns UInt, cast if selecting from SInt
e.tpe match {
case UIntType(_) => e2
case SIntType(_) => DoPrim(AsSInt, Seq(e2), Seq.empty, SIntType(IntWidth(i)))
}
case _ => e
}
}
// Recursive, updates expression so children exp's have correct widths
private def onExp(e: Expression): Expression = e map onExp match {
case Mux(cond, tval, fval, tpe) =>
Mux(cond, fixup(width(tpe))(tval), fixup(width(tpe))(fval), tpe)
case e: ValidIf => e copy (value = fixup(width(e.tpe))(e.value))
case e: DoPrim => e.op match {
case Lt | Leq | Gt | Geq | Eq | Neq | Not | And | Or | Xor |
Add | Sub | Mul | Div | Rem | Shr =>
// sensitive ops
e map fixup((e.args map width _ foldLeft 0)(math.max))
case Dshl =>
// special case as args aren't all same width
e copy (op = Dshlw, args = Seq(fixup(width(e.tpe))(e.args.head), e.args(1)))
case Shl =>
// special case as arg should be same width as result
e copy (op = Shlw, args = Seq(fixup(width(e.tpe))(e.args.head)))
case _ => e
}
case e => e
}
// Recursive. Fixes assignments and register initialization widths
private def onStmt(s: Statement): Statement = s map onExp match {
case s: Connect =>
s copy (expr = fixup(width(s.loc))(s.expr))
case s: DefRegister =>
s copy (init = fixup(width(s.tpe))(s.init))
case s => s map onStmt
}
def run(c: Circuit): Circuit = c copy (modules = (c.modules map (_ map onStmt)))
}
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