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/* NSC -- new Scala compiler
* Copyright 2005-2011 LAMP/EPFL
* @author Martin Odersky
*/
package scala.tools.nsc
package backend
package icode
import scala.collection.{ mutable, immutable }
import mutable.{ ArrayBuffer }
import util.{ Position, NoPosition }
import backend.icode.analysis.ProgramPoint
trait BasicBlocks {
self: ICodes =>
import opcodes._
import global.{ settings, log, nme }
import nme.isExceptionResultName
/** This class represents a basic block. Each
* basic block contains a list of instructions that are
* either executed all, or none. No jumps
* to/from the "middle" of the basic block are allowed (modulo exceptions).
*/
class BasicBlock(val label: Int, val method: IMethod)
extends AnyRef
with ProgramPoint[BasicBlock]
with Seq[Instruction] {
import BBFlags._
def code = method.code
/** Flags of this basic block. */
private var flags: Int = 0
/** Does this block have the given flag? */
def hasFlag(flag: Int): Boolean = (flags & flag) != 0
/** Set the given flag. */
private def setFlag(flag: Int): Unit = flags |= flag
private def resetFlag(flag: Int) {
flags &= ~flag
}
/** Is this block closed? */
def closed: Boolean = hasFlag(CLOSED)
def closed_=(b: Boolean) = if (b) setFlag(CLOSED) else resetFlag(CLOSED)
/** When set, the emit methods will be ignored. */
def ignore: Boolean = hasFlag(IGNORING)
def ignore_=(b: Boolean) = if (b) setFlag(IGNORING) else resetFlag(IGNORING)
/** Is this block the head of a while? */
def loopHeader = hasFlag(LOOP_HEADER)
def loopHeader_=(b: Boolean) =
if (b) setFlag(LOOP_HEADER) else resetFlag(LOOP_HEADER)
/** Is this block the start block of an exception handler? */
def exceptionHandlerStart = hasFlag(EX_HEADER)
def exceptionHandlerStart_=(b: Boolean) =
if (b) setFlag(EX_HEADER) else resetFlag(EX_HEADER)
/** Has this basic block been modified since the last call to 'successors'? */
def touched = hasFlag(DIRTYSUCCS)
def touched_=(b: Boolean) = if (b) {
setFlag(DIRTYSUCCS | DIRTYPREDS)
} else {
resetFlag(DIRTYSUCCS | DIRTYPREDS)
}
// basic blocks start in a dirty state
setFlag(DIRTYSUCCS | DIRTYPREDS)
/** Cached predecessors. */
var preds: List[BasicBlock] = null
/** Local variables that are in scope at entry of this basic block. Used
* for debugging information.
*/
var varsInScope: mutable.Set[Local] = new mutable.LinkedHashSet()
/** ICode instructions, used as temporary storage while emitting code.
* Once closed is called, only the `instrs' array should be used.
*/
private var instructionList: List[Instruction] = Nil
private var instrs: Array[Instruction] = _
override def toList: List[Instruction] =
if (closed) instrs.toList else instructionList.reverse
/** Return an iterator over the instructions in this basic block. */
def iterator: Iterator[Instruction] =
if (closed) instrs.iterator else instructionList.reverse.iterator
/** return the underlying array of instructions */
def getArray: Array[Instruction] = {
assert(closed)
instrs
}
def fromList(is: List[Instruction]) {
code.touched = true
instrs = is.toArray
closed = true
}
/** Return the index of inst. Uses reference equality.
* Returns -1 if not found.
*/
def indexOf(inst: Instruction): Int = {
assert(closed)
instrs indexWhere (_ eq inst)
}
/** Apply a function to all the instructions of the block. */
override def foreach[U](f: Instruction => U) = {
if (!closed) {
method.dump
global.abort("Traversing an open block!: " + label + " in " + method)
}
instrs foreach f
}
/** The number of instructions in this basic block so far. */
def length = if (closed) instrs.length else instructionList.length
/** Return the n-th instruction. */
def apply(n: Int): Instruction =
if (closed) instrs(n) else instructionList.reverse(n)
///////////////////// Substitutions ///////////////////////
/**
* Replace the instruction at the given position. Used by labels when
* they are anchored. It retains the position of the previous instruction.
*/
def replaceInstruction(pos: Int, instr: Instruction): Boolean = {
assert(closed, "Instructions can be replaced only after the basic block is closed")
instr.setPos(instrs(pos).pos)
instrs(pos) = instr
code.touched = true
true
}
/**
* Replace the given instruction with the new one.
* Returns `true' if it actually changed something.
* It retains the position of the previous instruction.
*/
def replaceInstruction(oldInstr: Instruction, newInstr: Instruction): Boolean = {
assert(closed, "Instructions can be replaced only after the basic block is closed")
indexOf(oldInstr) match {
case -1 => false
case idx =>
newInstr setPos oldInstr.pos
instrs(idx) = newInstr
code.touched = true
true
}
}
/** Replaces oldInstr with is. It does not update
* the position field in the newly inserted instructions, so it behaves
* differently than the one-instruction versions of this function.
*
* @param iold ..
* @param is ..
* @return ..
*/
def replaceInstruction(oldInstr: Instruction, is: List[Instruction]): Boolean = {
assert(closed, "Instructions can be replaced only after the basic block is closed")
indexOf(oldInstr) match {
case -1 => false
case idx =>
instrs = instrs.patch(idx, is, 1)
code.touched = true
true
}
}
/** Insert instructions in 'is' immediately after index 'idx'. */
def insertAfter(idx: Int, is: List[Instruction]) {
assert(closed, "Instructions can be replaced only after the basic block is closed")
instrs = instrs.patch(idx + 1, is, 0)
code.touched = true
}
/** Removes instructions found at the given positions.
*
* @param positions ...
*/
def removeInstructionsAt(positions: Int*) {
assert(closed)
instrs = instrs.indices.toArray filterNot positions.toSet map instrs
code.touched = true
}
/** Remove the last instruction of this basic block. It is
* fast for an open block, but slower when the block is closed.
*/
def removeLastInstruction() {
if (closed)
removeInstructionsAt(size)
else {
instructionList = instructionList.tail
code.touched = true
}
}
/** Replaces all instructions found in the map.
*
* @param map ...
*/
def subst(map: Map[Instruction, Instruction]): Unit =
if (!closed)
instructionList = instructionList map (x => map.getOrElse(x, x))
else
instrs.zipWithIndex collect {
case (oldInstr, i) if map contains oldInstr =>
code.touched |= replaceInstruction(i, map(oldInstr))
}
////////////////////// Emit //////////////////////
/** Add a new instruction at the end of the block,
* using the same source position as the last emitted instruction
*/
def emit(instr: Instruction) {
val pos = if (instructionList.isEmpty) NoPosition else instructionList.head.pos
emit(instr, pos)
}
/** Emitting does not set touched to true. During code generation this is a hotspot and
* setting the flag for each emit is a waste. Caching should happen only after a block
* is closed, which sets the DIRTYSUCCS flag.
*/
def emit(instr: Instruction, pos: Position) {
/* if (closed) {
print()
Console.println("trying to emit: " + instr)
} */
assert(!closed || ignore, "BasicBlock closed")
if (ignore) {
if (settings.debug.value) {
/** Trying to pin down what it's likely to see after a block has been
* put into ignore mode so we hear about it if there's a problem.
*/
instr match {
case JUMP(_) | RETURN(_) | THROW(_) | SCOPE_EXIT(_) => // ok
case STORE_LOCAL(local) if isExceptionResultName(local.sym.name) => // ok
case x => log("Ignoring instruction, possibly at our peril, at " + pos + ": " + x)
}
}
}
else {
instr.setPos(pos)
instructionList ::= instr
}
}
def emit(instrs: Seq[Instruction]) {
instrs foreach (i => emit(i, i.pos))
}
/** The semantics of this are a little odd but it's designed to work
* seamlessly with the existing code. It emits each supplied instruction,
* then closes the block. The odd part is that if the instruction has
* pos == NoPosition, it calls the 1-arg emit, but otherwise it calls
* the 2-arg emit. This way I could retain existing behavior exactly by
* calling setPos on any instruction using the two arg version which
* I wanted to include in a call to emitOnly.
*/
def emitOnly(instrs: Instruction*) {
instrs foreach (i => if (i.pos == NoPosition) emit(i) else emit(i, i.pos))
this.close
}
/** do nothing if block is already closed */
def closeWith(instr: Instruction) {
if (closed) () else {
emit(instr)
close
}
}
def closeWith(instr: Instruction, pos: Position) {
if (closed) () else {
emit(instr, pos)
close
}
}
/** Close the block */
def close() {
assert(!closed || ignore)
assert(instructionList.nonEmpty, "Empty block.")
closed = true
setFlag(DIRTYSUCCS)
instructionList = instructionList.reverse
instrs = instructionList.toArray
}
def open() {
assert(closed)
closed = false
ignore = false
touched = true
instructionList = instructionList.reverse // prepare for appending to the head
}
def clear() {
instructionList = Nil
instrs = null
preds = null
}
override def isEmpty: Boolean = instructionList.isEmpty
/** Enter ignore mode: new 'emit'ted instructions will not be
* added to this basic block. It makes the generation of THROW
* and RETURNs easier.
*/
def enterIgnoreMode() = {
ignore = true
}
def exitIgnoreMode() {
assert(ignore, "Exit ignore mode when not in ignore mode.")
ignore = false
}
/** Return the last instruction of this basic block. */
def lastInstruction =
if (closed) instrs.last
else instructionList.head
def firstInstruction =
if (closed) instrs(0)
else instructionList.last
def exceptionSuccessorsForBlock(block: BasicBlock): List[BasicBlock] =
method.exh collect { case x if x covers block => x.startBlock }
/** Cached value of successors. Must be recomputed whenever a block in the current method is changed. */
private var succs: List[BasicBlock] = Nil
private def updateSuccs() {
resetFlag(DIRTYSUCCS)
succs =
if (isEmpty) Nil
else exceptionSuccessors ++ directSuccessors ++ indirectExceptionSuccessors
}
def successors : List[BasicBlock] = {
if (touched) updateSuccs()
succs
}
def directSuccessors: List[BasicBlock] =
if (isEmpty) Nil else lastInstruction match {
case JUMP(whereto) => List(whereto)
case CJUMP(succ, fail, _, _) => fail :: succ :: Nil
case CZJUMP(succ, fail, _, _) => fail :: succ :: Nil
case SWITCH(_, labels) => labels
case RETURN(_) => Nil
case THROW(_) => Nil
case _ =>
if (closed) {
dump
global.abort("The last instruction is not a control flow instruction: " + lastInstruction)
}
else Nil
}
def exceptionSuccessors: List[BasicBlock] =
exceptionSuccessorsForBlock(this)
/** Return a list of successors for 'b' that come from exception handlers
* covering b's (non-exceptional) successors. These exception handlers
* might not cover 'b' itself. This situation corresponds to an
* exception being thrown as the first thing of one of b's successors.
*/
def indirectExceptionSuccessors: List[BasicBlock] =
directSuccessors flatMap exceptionSuccessorsForBlock distinct
/** Returns the predecessors of this block. */
def predecessors: List[BasicBlock] = {
if (hasFlag(DIRTYPREDS)) {
resetFlag(DIRTYPREDS)
preds = code.blocks.iterator filter (_.successors contains this) toList
}
preds
}
override def equals(other: Any): Boolean = other match {
case that: BasicBlock => (that.label == label) && (that.code == code)
case _ => false
}
override def hashCode = label * 41 + code.hashCode
// Instead of it, rather use a printer
def print() { print(java.lang.System.out) }
def print(out: java.io.PrintStream) {
out.println("block #"+label+" :")
foreach(i => out.println(" " + i))
out.print("Successors: ")
successors.foreach((x: BasicBlock) => out.print(" "+x.label.toString()))
out.println()
}
private def succString = if (successors.isEmpty) "[S: N/A]" else successors.distinct.mkString("[S: ", ", ", "]")
private def predString = if (predecessors.isEmpty) "[P: N/A]" else predecessors.distinct.mkString("[P: ", ", ", "]")
override def toString(): String = "" + label
def blockContents = {
def posStr(p: Position) = if (p.isDefined) p.line.toString else ""
val xs = this.toList map (instr => posStr(instr.pos) + "\t" + instr)
xs.mkString(fullString + " {\n ", "\n ", "\n}")
}
def predContents = predecessors.map(_.blockContents).mkString(predecessors.size + " preds:\n", "\n", "\n")
def succContents = successors.map(_.blockContents).mkString(successors.size + " succs:\n", "\n", "\n")
def fullString: String = List("Block", label, succString, predString, flagsString) mkString " "
def flagsString: String = BBFlags.flagsToString(flags)
}
}
object BBFlags {
val flagMap = Map[Int, String](
LOOP_HEADER -> "loopheader",
IGNORING -> "ignore",
EX_HEADER -> "exheader",
CLOSED -> "closed",
DIRTYSUCCS -> "dirtysuccs",
DIRTYPREDS -> "dirtypreds"
)
def flagsToString(flags: Int) = {
flagMap collect { case (bit, name) if (bit & flags) != 0 => "<" + name + ">" } mkString " "
}
/** This block is a loop header (was translated from a while). */
final val LOOP_HEADER = (1 << 0)
/** Ignoring mode: emit instructions are dropped. */
final val IGNORING = (1 << 1)
/** This block is the header of an exception handler. */
final val EX_HEADER = (1 << 2)
/** This block is closed. No new instructions can be added. */
final val CLOSED = (1 << 3)
/** Code has been changed, recompute successors. */
final val DIRTYSUCCS = (1 << 4)
/** Code has been changed, recompute predecessors. */
final val DIRTYPREDS = (1 << 5)
}
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