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/*
Copyright (c) 2014 - 2016 The Regents of the University of
California (Regents). All Rights Reserved. Redistribution and use in
source and binary forms, with or without modification, are permitted
provided that the following conditions are met:
* Redistributions of source code must retain the above
copyright notice, this list of conditions and the following
two paragraphs of disclaimer.
* Redistributions in binary form must reproduce the above
copyright notice, this list of conditions and the following
two paragraphs of disclaimer in the documentation and/or other materials
provided with the distribution.
* Neither the name of the Regents nor the names of its contributors
may be used to endorse or promote products derived from this
software without specific prior written permission.
IN NO EVENT SHALL REGENTS BE LIABLE TO ANY PARTY FOR DIRECT, INDIRECT,
SPECIAL, INCIDENTAL, OR CONSEQUENTIAL DAMAGES, INCLUDING LOST PROFITS,
ARISING OUT OF THE USE OF THIS SOFTWARE AND ITS DOCUMENTATION, EVEN IF
REGENTS HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
REGENTS SPECIFICALLY DISCLAIMS ANY WARRANTIES, INCLUDING, BUT NOT
LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
A PARTICULAR PURPOSE. THE SOFTWARE AND ACCOMPANYING DOCUMENTATION, IF
ANY, PROVIDED HEREUNDER IS PROVIDED "AS IS". REGENTS HAS NO OBLIGATION
TO PROVIDE MAINTENANCE, SUPPORT, UPDATES, ENHANCEMENTS, OR
MODIFICATIONS.
*/
package firrtl.passes
import firrtl._
import firrtl.Utils._
import firrtl.Mappers._
import annotation.tailrec
object ConstProp extends Pass {
def name = "Constant Propagation"
trait FoldLogicalOp {
def fold(c1: UIntValue, c2: UIntValue): UIntValue
def simplify(e: Expression, lhs: UIntValue, rhs: Expression): Expression
def apply(e: DoPrim): Expression = (e.args(0), e.args(1)) match {
case (lhs: UIntValue, rhs: UIntValue) => fold(lhs, rhs)
case (lhs: UIntValue, rhs) => simplify(e, lhs, rhs)
case (lhs, rhs: UIntValue) => simplify(e, rhs, lhs)
case _ => e
}
}
object FoldAND extends FoldLogicalOp {
def fold(c1: UIntValue, c2: UIntValue) = UIntValue(c1.value & c2.value, c1.width max c2.width)
def simplify(e: Expression, lhs: UIntValue, rhs: Expression) = lhs.width match {
case IntWidth(w) if long_BANG(tpe(rhs)) == w =>
if (lhs.value == 0) lhs // and(x, 0) => 0
else if (lhs.value == (BigInt(1) << w.toInt) - 1) rhs // and(x, 1) => x
else e
case _ => e
}
}
object FoldOR extends FoldLogicalOp {
def fold(c1: UIntValue, c2: UIntValue) = UIntValue(c1.value | c2.value, c1.width max c2.width)
def simplify(e: Expression, lhs: UIntValue, rhs: Expression) = lhs.width match {
case IntWidth(w) if long_BANG(tpe(rhs)) == w =>
if (lhs.value == 0) rhs // or(x, 0) => x
else if (lhs.value == (BigInt(1) << w.toInt) - 1) lhs // or(x, 1) => 1
else e
case _ => e
}
}
object FoldXOR extends FoldLogicalOp {
def fold(c1: UIntValue, c2: UIntValue) = UIntValue(c1.value ^ c2.value, c1.width max c2.width)
def simplify(e: Expression, lhs: UIntValue, rhs: Expression) = lhs.width match {
case IntWidth(w) if long_BANG(tpe(rhs)) == w =>
if (lhs.value == 0) rhs // xor(x, 0) => x
else e
case _ => e
}
}
object FoldEqual extends FoldLogicalOp {
def fold(c1: UIntValue, c2: UIntValue) = UIntValue(if (c1.value == c2.value) 1 else 0, IntWidth(1))
def simplify(e: Expression, lhs: UIntValue, rhs: Expression) = lhs.width match {
case IntWidth(w) if w == 1 && long_BANG(tpe(rhs)) == 1 =>
if (lhs.value == 1) rhs // eq(x, 1) => x
else e
case _ => e
}
}
object FoldNotEqual extends FoldLogicalOp {
def fold(c1: UIntValue, c2: UIntValue) = UIntValue(if (c1.value != c2.value) 1 else 0, IntWidth(1))
def simplify(e: Expression, lhs: UIntValue, rhs: Expression) = lhs.width match {
case IntWidth(w) if w == 1 && long_BANG(tpe(rhs)) == w =>
if (lhs.value == 0) rhs // neq(x, 0) => x
else e
case _ => e
}
}
private def constPropPrim(e: DoPrim): Expression = e.op match {
case SHIFT_RIGHT_OP => {
val amount = e.consts(0).toInt
def shiftWidth(w: Width) = (w - IntWidth(amount)) max IntWidth(1)
e.args(0) match {
// TODO when amount >= x.width, return a zero-width wire
case UIntValue(v, w) => UIntValue(v >> amount, shiftWidth(w))
// take sign bit if shift amount is larger than arg width
case SIntValue(v, w) => SIntValue(v >> amount, shiftWidth(w))
case _ => e
}
}
case AND_OP => FoldAND(e)
case OR_OP => FoldOR(e)
case XOR_OP => FoldXOR(e)
case EQUAL_OP => FoldEqual(e)
case NEQUAL_OP => FoldNotEqual(e)
case NOT_OP => e.args(0) match {
case UIntValue(v, IntWidth(w)) => UIntValue(v ^ ((BigInt(1) << w.toInt) - 1), IntWidth(w))
case _ => e
}
case BITS_SELECT_OP => e.args(0) match {
case UIntValue(v, w) => {
val hi = e.consts(0).toInt
val lo = e.consts(1).toInt
require(hi >= lo)
UIntValue((v >> lo) & ((BigInt(1) << (hi - lo + 1)) - 1), w)
}
case x if long_BANG(tpe(e)) == long_BANG(tpe(x)) => tpe(x) match {
case t: UIntType => x
case _ => DoPrim(AS_UINT_OP, Seq(x), Seq(), tpe(e))
}
case _ => e
}
case _ => e
}
private def constPropMuxCond(m: Mux) = (m.cond, tpe(m.tval), tpe(m.fval), m.tpe) match {
case (c: UIntValue, ttpe: UIntType, ftpe: UIntType, mtpe: UIntType) =>
if (c.value == 1 && ttpe == mtpe) m.tval
else if (c.value == 0 && ftpe == mtpe) m.fval
else m
case _ => m
}
private def constPropMux(m: Mux): Expression = (m.tval, m.fval) match {
case (t: UIntValue, f: UIntValue) =>
if (t == f) t
else if (t.value == 1 && f.value == 0 && long_BANG(m.tpe) == 1) m.cond
else constPropMuxCond(m)
case _ => constPropMuxCond(m)
}
private def constPropNodeRef(r: WRef, e: Expression) = e match {
case _: UIntValue | _: SIntValue | _: WRef => e
case _ => r
}
@tailrec
private def constPropModule(m: InModule): InModule = {
var nPropagated = 0L
val nodeMap = collection.mutable.HashMap[String, Expression]()
def constPropExpression(e: Expression): Expression = {
val old = e map constPropExpression
val propagated = old match {
case p: DoPrim => constPropPrim(p)
case m: Mux => constPropMux(m)
case r: WRef if nodeMap contains r.name => constPropNodeRef(r, nodeMap(r.name))
case x => x
}
if (old ne propagated)
nPropagated += 1
propagated
}
def constPropStmt(s: Stmt): Stmt = {
s match {
case x: DefNode => nodeMap(x.name) = x.value
case _ =>
}
s map constPropStmt map constPropExpression
}
val res = InModule(m.info, m.name, m.ports, constPropStmt(m.body))
if (nPropagated > 0) constPropModule(res) else res
}
def run(c: Circuit): Circuit = {
val modulesx = c.modules.map {
case m: ExModule => m
case m: InModule => constPropModule(m)
}
Circuit(c.info, modulesx, c.main)
}
}
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