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/* NSC -- new Scala compiler
* Copyright 2005-2013 LAMP/EPFL
* @author Martin Odersky
*/
package scala.tools.nsc
package backend.icode
package analysis
import scala.collection.{ mutable, immutable }
import immutable.ListSet
/** Compute reaching definitions. We are only interested in reaching
* definitions for local variables, since values on the stack
* behave as-if in SSA form: the closest instruction which produces a value
* on the stack is a reaching definition.
*/
abstract class ReachingDefinitions {
val global: Global
import global._
import icodes._
/** The lattice for reaching definitions. Elements are
* a triple (local variable, basic block, index of instruction of that basic block)
*/
object rdefLattice extends SemiLattice {
type Definition = (Local, BasicBlock, Int)
type Elem = IState[ListSet[Definition], Stack]
type StackPos = ListSet[(BasicBlock, Int)]
type Stack = List[StackPos]
private def referenceEqualSet(name: String) = new ListSet[Definition] with ReferenceEquality {
override def toString = "<" + name + ">"
}
val top: Elem = IState(referenceEqualSet("top"), Nil)
val bottom: Elem = IState(referenceEqualSet("bottom"), Nil)
/** The least upper bound is set inclusion for locals, and pairwise set inclusion for stacks. */
def lub2(exceptional: Boolean)(a: Elem, b: Elem): Elem = {
if (bottom == a) b
else if (bottom == b) a
else IState(a.vars ++ b.vars,
if (a.stack.isEmpty) b.stack
else if (b.stack.isEmpty) a.stack
else {
// !!! These stacks are with some frequency not of the same size.
// I can't reverse engineer the logic well enough to say whether this
// indicates a problem. Even if it doesn't indicate a problem,
// it'd be nice not to call zip with mismatched sequences because
// it makes it harder to spot the real problems.
val result = (a.stack, b.stack).zipped map (_ ++ _)
if (settings.debug && (a.stack.length != b.stack.length))
devWarning(s"Mismatched stacks in ReachingDefinitions#lub2: ${a.stack}, ${b.stack}, returning $result")
result
}
)
}
}
class ReachingDefinitionsAnalysis extends DataFlowAnalysis[rdefLattice.type] {
type P = BasicBlock
val lattice = rdefLattice
import lattice.{ Definition, Stack, Elem, StackPos }
var method: IMethod = _
val gen = mutable.Map[BasicBlock, ListSet[Definition]]()
val kill = mutable.Map[BasicBlock, ListSet[Local]]()
val drops = mutable.Map[BasicBlock, Int]()
val outStack = mutable.Map[BasicBlock, Stack]()
def init(m: IMethod) {
this.method = m
gen.clear()
kill.clear()
drops.clear()
outStack.clear()
m foreachBlock { b =>
val (g, k) = genAndKill(b)
val (d, st) = dropsAndGen(b)
gen += (b -> g)
kill += (b -> k)
drops += (b -> d)
outStack += (b -> st)
}
init {
m foreachBlock { b =>
worklist += b
in(b) = lattice.bottom
out(b) = lattice.bottom
}
m.exh foreach { e =>
in(e.startBlock) = lattice.IState(new ListSet[Definition], List(new StackPos))
}
}
}
import opcodes._
def genAndKill(b: BasicBlock): (ListSet[Definition], ListSet[Local]) = {
var genSet = ListSet[Definition]()
var killSet = ListSet[Local]()
for ((STORE_LOCAL(local), idx) <- b.toList.zipWithIndex) {
killSet = killSet + local
genSet = updateReachingDefinition(b, idx, genSet)
}
(genSet, killSet)
}
private def dropsAndGen(b: BasicBlock): (Int, Stack) = {
var depth, drops = 0
var stackOut: Stack = Nil
for ((instr, idx) <- b.toList.zipWithIndex) {
instr match {
case LOAD_EXCEPTION(_) => ()
case _ if instr.consumed > depth =>
drops += (instr.consumed - depth)
depth = 0
stackOut = Nil
case _ =>
stackOut = stackOut.drop(instr.consumed)
depth -= instr.consumed
}
var prod = instr.produced
depth += prod
while (prod > 0) {
stackOut ::= ListSet((b, idx))
prod -= 1
}
}
// Console.println("drops(" + b + ") = " + drops)
// Console.println("stackout(" + b + ") = " + stackOut)
(drops, stackOut)
}
override def run() {
forwardAnalysis(blockTransfer)
if (settings.debug) {
linearizer.linearize(method).foreach(b => if (b != method.startBlock)
assert(lattice.bottom != in(b),
"Block " + b + " in " + this.method + " has input equal to bottom -- not visited? " + in(b)
+ ": bot: " + lattice.bottom
+ "\nin(b) == bottom: " + (in(b) == lattice.bottom)
+ "\nbottom == in(b): " + (lattice.bottom == in(b))))
}
}
import opcodes._
import lattice.IState
def updateReachingDefinition(b: BasicBlock, idx: Int, rd: ListSet[Definition]): ListSet[Definition] = {
val STORE_LOCAL(local) = b(idx)
val tmp = local
(rd filter { case (l, _, _) => l != tmp }) + ((tmp, b, idx))
}
private def blockTransfer(b: BasicBlock, in: lattice.Elem): lattice.Elem = {
var locals: ListSet[Definition] = (in.vars filter { case (l, _, _) => !kill(b)(l) }) ++ gen(b)
if (locals eq lattice.bottom.vars) locals = new ListSet[Definition]
IState(locals, outStack(b) ::: in.stack.drop(drops(b)))
}
/** Return the reaching definitions corresponding to the point after idx. */
def interpret(b: BasicBlock, idx: Int, in: lattice.Elem): Elem = {
var locals = in.vars
var stack = in.stack
val instr = b(idx)
instr match {
case STORE_LOCAL(l1) =>
locals = updateReachingDefinition(b, idx, locals)
stack = stack.drop(instr.consumed)
case LOAD_EXCEPTION(_) =>
stack = Nil
case _ =>
stack = stack.drop(instr.consumed)
}
var prod = instr.produced
while (prod > 0) {
stack ::= ListSet((b, idx))
prod -= 1
}
IState(locals, stack)
}
/** Return the instructions that produced the 'm' elements on the stack, below given 'depth'.
* for instance, findefs(bb, idx, 1, 1) returns the instructions that might have produced the
* value found below the topmost element of the stack.
*/
def findDefs(bb: BasicBlock, idx: Int, m: Int, depth: Int): List[(BasicBlock, Int)] = if (idx > 0) {
assert(bb.closed, bb)
val instrs = bb.getArray
var res: List[(BasicBlock, Int)] = Nil
var i = idx
var n = m
var d = depth
// "I look for who produced the 'n' elements below the 'd' topmost slots of the stack"
while (n > 0 && i > 0) {
i -= 1
val prod = instrs(i).produced
if (prod > d) {
res = (bb, i) :: res
n = n - (prod - d)
instrs(i) match {
case LOAD_EXCEPTION(_) => ()
case _ => d = instrs(i).consumed
}
} else {
d -= prod
d += instrs(i).consumed
}
}
if (n > 0) {
val stack = this.in(bb).stack
assert(stack.length >= n, "entry stack is too small, expected: " + n + " found: " + stack)
stack.drop(d).take(n) foreach { defs =>
res = defs.toList ::: res
}
}
res
} else {
val stack = this.in(bb).stack
assert(stack.length >= m, "entry stack is too small, expected: " + m + " found: " + stack)
stack.drop(depth).take(m) flatMap (_.toList)
}
/** Return the definitions that produced the topmost 'm' elements on the stack,
* and that reach the instruction at index 'idx' in basic block 'bb'.
*/
def findDefs(bb: BasicBlock, idx: Int, m: Int): List[(BasicBlock, Int)] =
findDefs(bb, idx, m, 0)
override def toString: String = {
if (method eq null) "<null>"
else method.code.blocks map { b =>
" entry(%s) = %s\n".format(b, in(b)) +
" exit(%s) = %s\n".format(b, out(b))
} mkString ("ReachingDefinitions {\n", "\n", "\n}")
}
}
}
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