Scala example source code file (CopyPropagation.scala)
The CopyPropagation.scala Scala example source code
/* NSC -- new Scala compiler
* Copyright 2005-2013 LAMP/EPFL
* @author Martin Odersky
*/
package scala
package tools.nsc
package backend.icode.analysis
import scala.collection.{ mutable, immutable }
/** A modified copy-propagation like analysis. It
* is augmented with a record-like value which is used
* to represent closures.
*
* @author Iulian Dragos
*/
abstract class CopyPropagation {
val global: Global
import global._
import icodes._
/** Locations can be local variables, this, and fields. */
abstract sealed class Location
case class LocalVar(l: Local) extends Location
case class Field(r: Record, sym: Symbol) extends Location
case object This extends Location
/** Values that can be on the stack. */
sealed abstract class Value { }
case class Record(cls: Symbol, bindings: mutable.Map[Symbol, Value]) extends Value { }
/** The value of some location in memory. */
case class Deref(l: Location) extends Value
/** The boxed value of some location. */
case class Boxed(l: Location) extends Value
/** The constant value c. */
case class Const(c: Constant) extends Value
/** Unknown. */
case object Unknown extends Value
/** The bottom record. */
object AllRecords extends Record(NoSymbol, mutable.HashMap[Symbol, Value]())
/** The lattice for this analysis. */
object copyLattice extends SemiLattice {
type Bindings = mutable.Map[Location, Value]
def emptyBinding = mutable.HashMap[Location, Value]()
class State(val bindings: Bindings, var stack: List[Value]) {
override def hashCode = bindings.hashCode + stack.hashCode
/* comparison with bottom is reference equality! */
override def equals(that: Any): Boolean = that match {
case x: State =>
if ((this eq bottom) || (this eq top) || (x eq bottom) || (x eq top)) this eq x
else bindings == x.bindings && stack == x.stack
case _ =>
false
}
/* Return an alias for the given local. It returns the last
* local in the chain of aliased locals. Cycles are not allowed
* to exist (by construction).
*/
def getAlias(l: Local): Local = {
var target = l
var stop = false
while (bindings.isDefinedAt(LocalVar(target)) && !stop) {
bindings(LocalVar(target)) match {
case Deref(LocalVar(t)) => target = t
case _ => stop = true
}
}
target
}
/* Return the value bound to the given local. */
def getBinding(l: Local): Value = {
def loop(lv: Local): Option[Value] = (bindings get LocalVar(lv)) match {
case Some(Deref(LocalVar(t))) => loop(t)
case x => x
}
loop(l) getOrElse Deref(LocalVar(l))
}
/** Return a local which contains the same value as this field, if any.
* If the field holds a reference to a local, the returned value is the
* binding of that local.
*/
def getFieldValue(r: Record, f: Symbol): Option[Value] = r.bindings get f map {
case Deref(LocalVar(l)) => getBinding(l)
case target @ Deref(Field(r1, f1)) => getFieldValue(r1, f1) getOrElse target
case target => target
}
/** The same as getFieldValue, but never returns Record/Field values. Use
* this when you want to find a replacement for a field value (either a local,
* or a constant/this value).
*/
def getFieldNonRecordValue(r: Record, f: Symbol): Option[Value] = {
assert(r.bindings contains f, "Record " + r + " does not contain a field " + f)
r.bindings(f) match {
case Deref(LocalVar(l)) =>
val alias = getAlias(l)
val derefAlias = Deref(LocalVar(alias))
Some(getBinding(alias) match {
case Record(_, _) => derefAlias
case Deref(Field(r1, f1)) => getFieldNonRecordValue(r1, f1) getOrElse derefAlias
case Boxed(_) => derefAlias
case v => v
})
case Deref(Field(r1, f1)) => getFieldNonRecordValue(r1, f1)
case target @ Deref(This) => Some(target)
case target @ Const(k) => Some(target)
case _ => None
}
}
override def toString(): String =
"\nBindings: " + bindings + "\nStack: " + stack
def dup: State = {
val b: Bindings = mutable.HashMap()
b ++= bindings
new State(b, stack)
}
}
type Elem = State
val top = new State(emptyBinding, Nil)
val bottom = new State(emptyBinding, Nil)
val exceptionHandlerStack = Unknown :: Nil
def lub2(exceptional: Boolean)(a: Elem, b: Elem): Elem = {
if (a eq bottom) b
else if (b eq bottom) a
else if (a == b) a
else {
//assert(!(a.stack eq exceptionHandlerStack) && !(b.stack eq exceptionHandlerStack))
val resStack =
if (exceptional) exceptionHandlerStack
else {
// if (a.stack.length != b.stack.length)
// throw new LubException(a, b, "Invalid stacks in states: ");
(a.stack, b.stack).zipped map { (v1, v2) =>
if (v1 == v2) v1 else Unknown
}
}
/* if (a.stack.length != b.stack.length)
throw new LubException(a, b, "Invalid stacks in states: ");
val resStack = List.map2(a.stack, b.stack) { (v1, v2) =>
if (v1 == v2) v1 else Unknown
}
*/
val resBindings = mutable.HashMap[Location, Value]()
for ((k, v) <- a.bindings if b.bindings.isDefinedAt(k) && v == b.bindings(k))
resBindings += (k -> v)
new State(resBindings, resStack)
}
}
}
final class CopyAnalysis extends DataFlowAnalysis[copyLattice.type] {
type P = BasicBlock
val lattice = copyLattice
var method: IMethod = _
def init(m: IMethod) {
this.method = m
init {
worklist += m.startBlock
worklist ++= (m.exh map (_.startBlock))
m foreachBlock { b =>
in(b) = lattice.bottom
out(b) = lattice.bottom
assert(out.contains(b), out)
debuglog("CopyAnalysis added point: " + b)
}
m.exh foreach { e =>
in(e.startBlock) = new copyLattice.State(copyLattice.emptyBinding, copyLattice.exceptionHandlerStack)
}
// first block is special: it's not bottom, but a precisely defined state with no bindings
in(m.startBlock) = new lattice.State(lattice.emptyBinding, Nil)
}
}
override def run() {
forwardAnalysis(blockTransfer)
if (settings.debug) {
linearizer.linearize(method).foreach(b => if (b != method.startBlock)
assert(in(b) != lattice.bottom,
"Block " + b + " in " + this.method + " has input equal to bottom -- not visited?"))
}
}
def blockTransfer(b: BasicBlock, in: lattice.Elem): lattice.Elem =
b.iterator.foldLeft(in)(interpret)
import opcodes._
private def retain[A, B](map: mutable.Map[A, B])(p: (A, B) => Boolean) = {
for ((k, v) <- map ; if !p(k, v)) map -= k
map
}
/** Abstract interpretation for one instruction. */
def interpret(in: copyLattice.Elem, i: Instruction): copyLattice.Elem = {
var out = in.dup
debuglog("- " + i + "\nin: " + in + "\n")
i match {
case THIS(_) =>
out.stack = Deref(This) :: out.stack
case CONSTANT(k) =>
if (k.tag != UnitTag)
out.stack = Const(k) :: out.stack
case LOAD_ARRAY_ITEM(_) =>
out.stack = (Unknown :: out.stack.drop(2))
case LOAD_LOCAL(local) =>
out.stack = Deref(LocalVar(local)) :: out.stack
case LOAD_FIELD(field, isStatic) =>
if (isStatic)
out.stack = Unknown :: out.stack; /* ignore static fields */
else {
val v1 = in.stack match {
case (r @ Record(cls, bindings)) :: xs =>
Deref(Field(r, field))
case Deref(LocalVar(l)) :: _ =>
in.getBinding(l) match {
case r @ Record(cls, bindings) => Deref(Field(r, field))
case _ => Unknown
}
case Deref(Field(r, f)) :: _ =>
val fld = in.getFieldValue(r, f)
fld match {
case Some(r @ Record(cls, bindings)) if bindings.isDefinedAt(f) =>
in.getFieldValue(r, f).getOrElse(Unknown)
case _ => Unknown
}
case _ => Unknown
}
out.stack = v1 :: out.stack.drop(1)
}
case LOAD_MODULE(module) =>
out.stack = Unknown :: out.stack
case STORE_ARRAY_ITEM(kind) =>
out.stack = out.stack.drop(3)
case STORE_LOCAL(local) =>
cleanReferencesTo(out, LocalVar(local))
in.stack match {
case Unknown :: xs => ()
case v :: vs =>
v match {
case Deref(LocalVar(other)) =>
if (other != local)
out.bindings += (LocalVar(local) -> v)
case _ =>
out.bindings += (LocalVar(local) -> v)
}
case Nil =>
sys.error("Incorrect icode in " + method + ". Expecting something on the stack.")
}
out.stack = out.stack drop 1
case STORE_THIS(_) =>
cleanReferencesTo(out, This)
out.stack = out.stack drop 1
case STORE_FIELD(field, isStatic) =>
if (isStatic)
out.stack = out.stack.drop(1)
else {
out.stack = out.stack.drop(2)
cleanReferencesTo(out, Field(AllRecords, field))
in.stack match {
case v :: Record(_, bindings) :: vs =>
bindings += (field -> v)
case _ => ()
}
}
case CALL_PRIMITIVE(primitive) =>
// TODO: model primitives
out.stack = Unknown :: out.stack.drop(i.consumed)
case CALL_METHOD(method, style) => style match {
case Dynamic =>
out = simulateCall(in, method, static = false)
case Static(onInstance) =>
if (onInstance) {
val obj = out.stack.drop(method.info.paramTypes.length).head
// if (method.isPrimaryConstructor) {
if (method.isPrimaryConstructor) {
obj match {
case Record(_, bindings) =>
for (v <- out.stack.take(method.info.paramTypes.length + 1)
if v ne obj) {
bindings ++= getBindingsForPrimaryCtor(in, method)
}
case _ => ()
}
// put the Record back on the stack and remove the 'returned' value
out.stack = out.stack.drop(1 + method.info.paramTypes.length)
} else
out = simulateCall(in, method, static = false)
} else
out = simulateCall(in, method, static = true)
case SuperCall(_) =>
out = simulateCall(in, method, static = false)
}
case BOX(tpe) =>
val top = out.stack.head match {
case Deref(loc) => Boxed(loc)
case _ => Unknown
}
out.stack = top :: out.stack.tail
case UNBOX(tpe) =>
val top = out.stack.head
top match {
case Boxed(loc) => Deref(loc) :: out.stack.tail
case _ => out.stack = Unknown :: out.stack.drop(1)
}
case NEW(kind) =>
val v1 = kind match {
case REFERENCE(cls) => Record(cls, mutable.HashMap[Symbol, Value]())
case _ => Unknown
}
out.stack = v1 :: out.stack
case CREATE_ARRAY(elem, dims) =>
out.stack = Unknown :: out.stack.drop(dims)
case IS_INSTANCE(tpe) =>
out.stack = Unknown :: out.stack.drop(1)
case CHECK_CAST(tpe) =>
out.stack = Unknown :: out.stack.drop(1)
case SWITCH(tags, labels) =>
out.stack = out.stack.drop(1)
case JUMP(whereto) =>
()
case CJUMP(success, failure, cond, kind) =>
out.stack = out.stack.drop(2)
case CZJUMP(success, failure, cond, kind) =>
out.stack = out.stack.drop(1)
case RETURN(kind) =>
if (kind != UNIT)
out.stack = out.stack.drop(1)
case THROW(_) =>
out.stack = out.stack.drop(1)
case DROP(kind) =>
out.stack = out.stack.drop(1)
case DUP(kind) =>
out.stack = out.stack.head :: out.stack
case MONITOR_ENTER() =>
out.stack = out.stack.drop(1)
case MONITOR_EXIT() =>
out.stack = out.stack.drop(1)
case SCOPE_ENTER(_) | SCOPE_EXIT(_) =>
()
case LOAD_EXCEPTION(_) =>
out.stack = Unknown :: Nil
case _ =>
dumpClassesAndAbort("Unknown instruction: " + i)
}
out
} /* def interpret */
/** Remove all references to this local variable from both stack
* and bindings. It is called when a new assignment destroys
* previous copy-relations.
*/
final def cleanReferencesTo(s: copyLattice.State, target: Location) {
def cleanRecord(r: Record): Record = {
retain(r.bindings) { (loc, value) =>
(value match {
case Deref(loc1) if (loc1 == target) => false
case Boxed(loc1) if (loc1 == target) => false
case _ => true
}) && (target match {
case Field(AllRecords, sym1) => !(loc == sym1)
case _ => true
})
}
r
}
s.stack = s.stack map { v => v match {
case Record(_, bindings) =>
cleanRecord(v.asInstanceOf[Record])
case Boxed(loc1) if (loc1 == target) => Unknown
case _ => v
}}
retain(s.bindings) { (loc, value) =>
(value match {
case Deref(loc1) if (loc1 == target) => false
case Boxed(loc1) if (loc1 == target) => false
case rec @ Record(_, _) =>
cleanRecord(rec)
true
case _ => true
}) &&
(loc match {
case l: Location if (l == target) => false
case _ => true
})
}
}
/** Update the state `s` after the call to `method`.
* The stack elements are dropped and replaced by the result of the call.
* If the method is impure, all bindings to record fields are cleared.
*/
final def simulateCall(state: copyLattice.State, method: Symbol, static: Boolean): copyLattice.State = {
val out = new copyLattice.State(state.bindings, state.stack)
out.stack = out.stack.drop(method.info.paramTypes.length + (if (static) 0 else 1))
if (method.info.resultType != definitions.UnitTpe && !method.isConstructor)
out.stack = Unknown :: out.stack
if (!isPureMethod(method))
invalidateRecords(out)
out
}
/** Drop everything known about mutable record fields.
*
* A simple escape analysis would help here. Some of the records we
* track never leak to other methods, therefore they can not be changed.
* We should not drop their bindings in this case. A closure object
* would be such an example. Some complications:
*
* - outer pointers. An closure escapes as an outer pointer to another
* nested closure.
*/
final def invalidateRecords(state: copyLattice.State) {
def shouldRetain(sym: Symbol): Boolean = {
if (sym.isMutable)
log("dropping binding for " + sym.fullName)
!sym.isMutable
}
state.stack = state.stack map { v => v match {
case Record(cls, bindings) =>
retain(bindings) { (sym, _) => shouldRetain(sym) }
Record(cls, bindings)
case _ => v
}}
retain(state.bindings) { (loc, value) =>
value match {
case Deref(Field(rec, sym)) => shouldRetain(sym)
case Boxed(Field(rec, sym)) => shouldRetain(sym)
case _ => true
}
}
}
/** Return bindings from an object fields to the values on the stack. This
* method has to find the correct mapping from fields to the order in which
* they are passed on the stack. It works for primary constructors.
*/
private def getBindingsForPrimaryCtor(in: copyLattice.State, ctor: Symbol): mutable.Map[Symbol, Value] = {
val paramAccessors = ctor.owner.constrParamAccessors
var values = in.stack.take(1 + ctor.info.paramTypes.length).reverse.drop(1)
val bindings = mutable.HashMap[Symbol, Value]()
debuglog("getBindings for: " + ctor + " acc: " + paramAccessors)
var paramTypes = ctor.tpe.paramTypes
val diff = paramTypes.length - paramAccessors.length
diff match {
case 0 => ()
case 1 if ctor.tpe.paramTypes.head == ctor.owner.rawowner.tpe =>
// it's an unused outer
debuglog("considering unused outer at position 0 in " + ctor.tpe.paramTypes)
paramTypes = paramTypes.tail
values = values.tail
case _ =>
debuglog("giving up on " + ctor + "(diff: " + diff + ")")
return bindings
}
// this relies on having the same order in paramAccessors and
// the arguments on the stack. It should be the same!
for ((p, i) <- paramAccessors.zipWithIndex) {
// assert(p.tpe == paramTypes(i), "In: " + ctor.fullName
// + " having acc: " + (paramAccessors map (_.tpe))+ " vs. params" + paramTypes
// + "\n\t failed at pos " + i + " with " + p.tpe + " == " + paramTypes(i))
if (p.tpe == paramTypes(i))
bindings += (p -> values.head)
values = values.tail
}
debuglog("\t" + bindings)
bindings
}
/** Is symbol `m` a pure method?
*/
final def isPureMethod(m: Symbol): Boolean =
m.isGetter // abstract getters are still pure, as we 'know'
final override def toString() = (
if (method eq null) List("<null>")
else method.blocks map { b =>
"\nIN(%s):\t Bindings: %s".format(b.label, in(b).bindings) +
"\nIN(%s):\t Stack: %s".format(b.label, in(b).stack)
}
).mkString
} /* class CopyAnalysis */
}
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