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|
/* NSC -- new Scala compiler
* Copyright 2005-2010 LAMP/EPFL
* @author Martin Odersky
*/
// $Id$
package scala.tools.nsc
package backend
package icode
//import scala.tools.nsc.ast._
import scala.collection.mutable.{Map, Set}
import scala.collection.mutable.LinkedHashSet
import scala.tools.nsc.util.{Position,NoPosition}
import scala.tools.nsc.backend.icode.analysis.ProgramPoint
trait BasicBlocks {
self: ICodes =>
import opcodes._
/** 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 <code>emit</code> 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: Set[Local] = new 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 _lastInstruction: Instruction = null
private var instrs: Array[Instruction] = _
override def toList: List[Instruction] = {
if (closed)
instrs.toList
else instructionList
}
/** 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 = toInstructionArray(is)
closed = true
}
/** Return the index of inst. Uses reference equality.
* Returns -1 if not found.
*/
def indexOf(inst: Instruction): Int = {
assert(closed)
var i = 0
while (i < instrs.length) {
if (instrs(i) eq inst) return i
i += 1
}
-1
}
/** Compute an hashCode for the block */
// override def hashCode() = label;
/** Apply a function to all the instructions of the block. */
override def foreach[U](f: Instruction => U) = {
if (!closed) {
dump
global.abort("Traversing an open block!: " + label)
}
instrs foreach f
}
/** The number of instructions in this basic block so far. */
def length: Int =
if (closed) instrs.length else instructionList.length
/** Return the index of the instruction which produced the value
* consumed by the given instruction.
*/
def findDef(pos: Int): Option[Int] = {
assert(closed)
var i = pos
var d = 0
while (i > 0) {
i -= 1
val prod = instrs(i).produced
if (prod > 0 && d == 0)
return Some(i)
d += (instrs(i).consumed - instrs(i).produced)
}
None
}
/** 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")
var i = 0
var changed = false
while (i < instrs.length && !changed) {
if (instrs(i) eq oldInstr) {
newInstr.setPos(oldInstr.pos)
instrs(i) = newInstr
changed = true
code.touched = true
}
i += 1
}
changed
}
/** Replaces <code>iold</code> with <code>is</code>. 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(iold: Instruction, is: List[Instruction]): Boolean = {
assert(closed, "Instructions can be replaced only after the basic block is closed")
var i = 0
var changed = false
while (i < instrs.length && (instrs(i) ne iold))
i += 1
if (i < instrs.length) {
val newInstrs = new Array[Instruction](instrs.length + is.length - 1);
changed = true
code.touched = true
Array.copy(instrs, 0, newInstrs, 0, i)
var j = i
for (x <- is) {
newInstrs(j) = x
j += 1
}
if (i + 1 < instrs.length)
Array.copy(instrs, i + 1, newInstrs, j, instrs.length - i - 1)
instrs = newInstrs;
}
changed
}
/** 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")
var i = idx + 1
if (i < instrs.length) {
val newInstrs = new Array[Instruction](instrs.length + is.length);
Array.copy(instrs, 0, newInstrs, 0, i)
var j = i
for (x <- is) {
newInstrs(j) = x
j += 1
}
if (i + 1 < instrs.length)
Array.copy(instrs, i + 1, newInstrs, j, instrs.length - i)
instrs = newInstrs;
}
code.touched = true
}
/** Removes instructions found at the given positions.
*
* @param positions ...
*/
def removeInstructionsAt(positions: Int*) {
assert(closed)
val removed = positions.toList
val newInstrs = new Array[Instruction](instrs.length - positions.length)
var i = 0
var j = 0
while (i < instrs.length) {
if (!removed.contains(i)) {
newInstrs(j) = instrs(i)
j += 1
}
i += 1
}
instrs = newInstrs
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]) {
if (!closed) substOnList(map) else {
var i = 0
while (i < instrs.length) {
map get instrs(i) match {
case Some(instr) =>
val changed = replaceInstruction(i, instr)
code.touched |= changed
case None => ()
}
i += 1
}
}
}
private def substOnList(map: Map[Instruction, Instruction]) {
def subst(l: List[Instruction]): List[Instruction] = l match {
case Nil => Nil
case x :: xs =>
map.get(x) match {
case Some(newInstr) => newInstr :: subst(xs)
case None => x :: subst(xs)
}
}
instructionList = subst(instructionList)
}
////////////////////// 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) {
if (!instructionList.isEmpty)
emit(instr, instructionList.head.pos)
else
emit(instr, NoPosition)
}
/** 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) {
instr.setPos(pos)
instructionList = instr :: instructionList
_lastInstruction = 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
}
/** Close the block */
def close {
assert(instructionList.length > 0, "Empty block.")
closed = true
setFlag(DIRTYSUCCS)
instructionList = instructionList.reverse
instrs = toInstructionArray(instructionList)
}
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(instrs.length - 1)
else
instructionList.head
def firstInstruction =
if (closed)
instrs(0)
else
instructionList.last
/** Convert the list to an array */
private def toInstructionArray(l: List[Instruction]): Array[Instruction] = {
var array = new Array[Instruction](l.length)
var i: Int = 0
l foreach (x => { array(i) = x; i += 1 })
array
}
/** Cached value of successors. Must be recomputed whenver a block in the current method is changed. */
private var succs: List[BasicBlock] = Nil
def successors : List[BasicBlock] = {
if (touched) {
resetFlag(DIRTYSUCCS)
succs = if (isEmpty) Nil else {
var res = lastInstruction match {
case JUMP(whereto) => List(whereto)
case CJUMP(success, failure, _, _) => failure :: success :: Nil
case CZJUMP(success, failure, _, _) => failure :: success :: 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
}
method.exh.foreach {
e: ExceptionHandler =>
if (e.covers(this)) res = e.startBlock :: res
}
val res1 = res ++ exceptionalSucc(this, res)
res1
}
}
// println("reusing cached successors for " + this + " in method " + method)
succs
}
def directSuccessors: List[BasicBlock] = {
if (isEmpty) Nil else lastInstruction match {
case JUMP(whereto) => List(whereto)
case CJUMP(success, failure, _, _) => failure :: success :: Nil
case CZJUMP(success, failure, _, _) => failure :: success :: 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
}
}
/** 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.
*/
private def exceptionalSucc(b: BasicBlock, succs: List[BasicBlock]): List[BasicBlock] = {
def findSucc(s: BasicBlock): List[BasicBlock] = {
val ss = method.exh flatMap { h =>
if (h.covers(s) /*&& mayThrow(h.startBlock.firstInstruction)*/) List(h.startBlock) else Nil
}
ss ++ (ss flatMap findSucc)
}
succs.flatMap(findSucc).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()
}
def fullString: String = {
val buf = new StringBuilder()
buf.append("Block ").append(label.toString())
buf.append("\nSuccessors: ").append(successors)
buf.append("\nPredecessors: ").append(predecessors)
buf.toString()
}
override def toString(): String = "" + label
def flagsString: String =
("block " + label + (
if (hasFlag(LOOP_HEADER)) " <loopheader> "
else if (hasFlag(IGNORING)) " <ignore> "
else if (hasFlag(EX_HEADER)) " <exheader> "
else if (hasFlag(CLOSED)) " <closed> "
else if (hasFlag(DIRTYSUCCS)) " <dirtysuccs> "
else if (hasFlag(DIRTYPREDS)) " <dirtypreds> "
else ""
))
}
}
object BBFlags {
/** This block is a loop header (was translated from a while). */
final val LOOP_HEADER = 0x00000001
/** Ignoring mode: emit instructions are dropped. */
final val IGNORING = 0x00000002
/** This block is the header of an exception handler. */
final val EX_HEADER = 0x00000004
/** This block is closed. No new instructions can be added. */
final val CLOSED = 0x00000008
/** Code has been changed, recompute successors. */
final val DIRTYSUCCS = 0x00000010
/** Code has been changed, recompute predecessors. */
final val DIRTYPREDS = 0x00000020
}
|