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/*
* Copyright (C) 2007 The Android Open Source Project
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.snapscript.dx.ssa;
import java.util.ArrayList;
import java.util.BitSet;
import java.util.Collections;
import java.util.Comparator;
import java.util.List;
import org.snapscript.dx.rop.code.BasicBlock;
import org.snapscript.dx.rop.code.BasicBlockList;
import org.snapscript.dx.rop.code.Insn;
import org.snapscript.dx.rop.code.InsnList;
import org.snapscript.dx.rop.code.PlainInsn;
import org.snapscript.dx.rop.code.RegisterSpec;
import org.snapscript.dx.rop.code.RegisterSpecList;
import org.snapscript.dx.rop.code.Rop;
import org.snapscript.dx.rop.code.RopMethod;
import org.snapscript.dx.rop.code.Rops;
import org.snapscript.dx.rop.code.SourcePosition;
import org.snapscript.dx.util.Hex;
import org.snapscript.dx.util.IntList;
import org.snapscript.dx.util.IntSet;
/**
* An SSA representation of a basic block.
*/
public final class SsaBasicBlock {
/**
* {@code non-null;} comparator for instances of this class that
* just compares block labels
*/
public static final Comparator LABEL_COMPARATOR =
new LabelComparator();
/** {@code non-null;} insn list associated with this instance */
private ArrayList insns;
/** {@code non-null;} predecessor set (by block list index) */
private BitSet predecessors;
/** {@code non-null;} successor set (by block list index) */
private BitSet successors;
/**
* {@code non-null;} ordered successor list
* (same block may be listed more than once)
*/
private IntList successorList;
/**
* block list index of primary successor, or {@code -1} for no primary
* successor
*/
private int primarySuccessor = -1;
/** label of block in rop form */
private int ropLabel;
/** {@code non-null;} method we belong to */
private SsaMethod parent;
/** our index into parent.getBlock() */
private int index;
/** list of dom children */
private final ArrayList domChildren;
/**
* the number of moves added to the end of the block during the
* phi-removal process. Retained for subsequent move scheduling.
*/
private int movesFromPhisAtEnd = 0;
/**
* the number of moves added to the beginning of the block during the
* phi-removal process. Retained for subsequent move scheduling.
*/
private int movesFromPhisAtBeginning = 0;
/**
* contains last computed value of reachability of this block, or -1
* if reachability hasn't been calculated yet
*/
private int reachable = -1;
/**
* {@code null-ok;} indexed by reg: the regs that are live-in at
* this block
*/
private IntSet liveIn;
/**
* {@code null-ok;} indexed by reg: the regs that are live-out at
* this block
*/
private IntSet liveOut;
/**
* Creates a new empty basic block.
*
* @param basicBlockIndex index this block will have
* @param ropLabel original rop-form label
* @param parent method of this block
*/
public SsaBasicBlock(final int basicBlockIndex, final int ropLabel,
final SsaMethod parent) {
this.parent = parent;
this.index = basicBlockIndex;
this.insns = new ArrayList();
this.ropLabel = ropLabel;
this.predecessors = new BitSet(parent.getBlocks().size());
this.successors = new BitSet(parent.getBlocks().size());
this.successorList = new IntList();
domChildren = new ArrayList();
}
/**
* Creates a new SSA basic block from a ROP form basic block.
*
* @param rmeth original method
* @param basicBlockIndex index this block will have
* @param parent method of this block predecessor set will be
* updated
* @return new instance
*/
public static SsaBasicBlock newFromRop(RopMethod rmeth,
int basicBlockIndex, final SsaMethod parent) {
BasicBlockList ropBlocks = rmeth.getBlocks();
BasicBlock bb = ropBlocks.get(basicBlockIndex);
SsaBasicBlock result =
new SsaBasicBlock(basicBlockIndex, bb.getLabel(), parent);
InsnList ropInsns = bb.getInsns();
result.insns.ensureCapacity(ropInsns.size());
for (int i = 0, sz = ropInsns.size() ; i < sz ; i++) {
result.insns.add(new NormalSsaInsn (ropInsns.get(i), result));
}
result.predecessors = SsaMethod.bitSetFromLabelList(
ropBlocks,
rmeth.labelToPredecessors(bb.getLabel()));
result.successors
= SsaMethod.bitSetFromLabelList(ropBlocks, bb.getSuccessors());
result.successorList
= SsaMethod.indexListFromLabelList(ropBlocks,
bb.getSuccessors());
if (result.successorList.size() != 0) {
int primarySuccessor = bb.getPrimarySuccessor();
result.primarySuccessor = (primarySuccessor < 0)
? -1 : ropBlocks.indexOfLabel(primarySuccessor);
}
return result;
}
/**
* Adds a basic block as a dom child for this block. Used when constructing
* the dom tree.
*
* @param child {@code non-null;} new dom child
*/
public void addDomChild(SsaBasicBlock child) {
domChildren.add(child);
}
/**
* Gets the dom children for this node. Don't modify this list.
*
* @return {@code non-null;} list of dom children
*/
public ArrayList getDomChildren() {
return domChildren;
}
/**
* Adds a phi insn to the beginning of this block. The result type of
* the phi will be set to void, to indicate that it's currently unknown.
*
* @param reg {@code >=0;} result reg
*/
public void addPhiInsnForReg(int reg) {
insns.add(0, new PhiInsn(reg, this));
}
/**
* Adds a phi insn to the beginning of this block. This is to be used
* when the result type or local-association can be determined at phi
* insert time.
*
* @param resultSpec {@code non-null;} reg
*/
public void addPhiInsnForReg(RegisterSpec resultSpec) {
insns.add(0, new PhiInsn(resultSpec, this));
}
/**
* Adds an insn to the head of this basic block, just after any phi
* insns.
*
* @param insn {@code non-null;} rop-form insn to add
*/
public void addInsnToHead(Insn insn) {
SsaInsn newInsn = SsaInsn.makeFromRop(insn, this);
insns.add(getCountPhiInsns(), newInsn);
parent.onInsnAdded(newInsn);
}
/**
* Replaces the last insn in this block. The provided insn must have
* some branchingness.
*
* @param insn {@code non-null;} rop-form insn to add, which must branch.
*/
public void replaceLastInsn(Insn insn) {
if (insn.getOpcode().getBranchingness() == Rop.BRANCH_NONE) {
throw new IllegalArgumentException("last insn must branch");
}
SsaInsn oldInsn = insns.get(insns.size() - 1);
SsaInsn newInsn = SsaInsn.makeFromRop(insn, this);
insns.set(insns.size() - 1, newInsn);
parent.onInsnRemoved(oldInsn);
parent.onInsnAdded(newInsn);
}
/**
* Visits each phi insn.
*
* @param v {@code non-null;} the callback
*/
public void forEachPhiInsn(PhiInsn.Visitor v) {
int sz = insns.size();
for (int i = 0; i < sz; i++) {
SsaInsn insn = insns.get(i);
if (insn instanceof PhiInsn) {
v.visitPhiInsn((PhiInsn) insn);
} else {
/*
* Presently we assume PhiInsn's are in a continuous
* block at the top of the list
*/
break;
}
}
}
/**
* Deletes all phi insns. Do this after adding appropriate move insns.
*/
public void removeAllPhiInsns() {
/*
* Presently we assume PhiInsn's are in a continuous
* block at the top of the list.
*/
insns.subList(0, getCountPhiInsns()).clear();
}
/**
* Gets the number of phi insns at the top of this basic block.
*
* @return count of phi insns
*/
private int getCountPhiInsns() {
int countPhiInsns;
int sz = insns.size();
for (countPhiInsns = 0; countPhiInsns < sz; countPhiInsns++) {
SsaInsn insn = insns.get(countPhiInsns);
if (!(insn instanceof PhiInsn)) {
break;
}
}
return countPhiInsns;
}
/**
* @return {@code non-null;} the (mutable) instruction list for this block,
* with phi insns at the beginning
*/
public ArrayList getInsns() {
return insns;
}
/**
* @return {@code non-null;} the (mutable) list of phi insns for this block
*/
public List getPhiInsns() {
return insns.subList(0, getCountPhiInsns());
}
/**
* @return the block index of this block
*/
public int getIndex() {
return index;
}
/**
* @return the label of this block in rop form
*/
public int getRopLabel() {
return ropLabel;
}
/**
* @return the label of this block in rop form as a hex string
*/
public String getRopLabelString() {
return Hex.u2(ropLabel);
}
/**
* @return {@code non-null;} predecessors set, indexed by block index
*/
public BitSet getPredecessors() {
return predecessors;
}
/**
* @return {@code non-null;} successors set, indexed by block index
*/
public BitSet getSuccessors() {
return successors;
}
/**
* @return {@code non-null;} ordered successor list, containing block
* indicies
*/
public IntList getSuccessorList() {
return successorList;
}
/**
* @return {@code >= -1;} block index of primary successor or
* {@code -1} if no primary successor
*/
public int getPrimarySuccessorIndex() {
return primarySuccessor;
}
/**
* @return rop label of primary successor
*/
public int getPrimarySuccessorRopLabel() {
return parent.blockIndexToRopLabel(primarySuccessor);
}
/**
* @return {@code null-ok;} the primary successor block or {@code null}
* if there is none
*/
public SsaBasicBlock getPrimarySuccessor() {
if (primarySuccessor < 0) {
return null;
} else {
return parent.getBlocks().get(primarySuccessor);
}
}
/**
* @return successor list of rop labels
*/
public IntList getRopLabelSuccessorList() {
IntList result = new IntList(successorList.size());
int sz = successorList.size();
for (int i = 0; i < sz; i++) {
result.add(parent.blockIndexToRopLabel(successorList.get(i)));
}
return result;
}
/**
* @return {@code non-null;} method that contains this block
*/
public SsaMethod getParent() {
return parent;
}
/**
* Inserts a new empty GOTO block as a predecessor to this block.
* All previous predecessors will be predecessors to the new block.
*
* @return {@code non-null;} an appropriately-constructed instance
*/
public SsaBasicBlock insertNewPredecessor() {
SsaBasicBlock newPred = parent.makeNewGotoBlock();
// Update the new block.
newPred.predecessors = predecessors;
newPred.successors.set(index) ;
newPred.successorList.add(index);
newPred.primarySuccessor = index;
// Update us.
predecessors = new BitSet(parent.getBlocks().size());
predecessors.set(newPred.index);
// Update our (soon-to-be) old predecessors.
for (int i = newPred.predecessors.nextSetBit(0); i >= 0;
i = newPred.predecessors.nextSetBit(i + 1)) {
SsaBasicBlock predBlock = parent.getBlocks().get(i);
predBlock.replaceSuccessor(index, newPred.index);
}
return newPred;
}
/**
* Constructs and inserts a new empty GOTO block {@code Z} between
* this block ({@code A}) and a current successor block
* ({@code B}). The new block will replace B as A's successor and
* A as B's predecessor. A and B will no longer be directly connected.
* If B is listed as a successor multiple times, all references
* are replaced.
*
* @param other current successor (B)
* @return {@code non-null;} an appropriately-constructed instance
*/
public SsaBasicBlock insertNewSuccessor(SsaBasicBlock other) {
SsaBasicBlock newSucc = parent.makeNewGotoBlock();
if (!successors.get(other.index)) {
throw new RuntimeException("Block " + other.getRopLabelString()
+ " not successor of " + getRopLabelString());
}
// Update the new block.
newSucc.predecessors.set(this.index);
newSucc.successors.set(other.index) ;
newSucc.successorList.add(other.index);
newSucc.primarySuccessor = other.index;
// Update us.
for (int i = successorList.size() - 1 ; i >= 0; i--) {
if (successorList.get(i) == other.index) {
successorList.set(i, newSucc.index);
}
}
if (primarySuccessor == other.index) {
primarySuccessor = newSucc.index;
}
successors.clear(other.index);
successors.set(newSucc.index);
// Update "other".
other.predecessors.set(newSucc.index);
other.predecessors.set(index, successors.get(other.index));
return newSucc;
}
/**
* Replaces an old successor with a new successor. This will throw
* RuntimeException if {@code oldIndex} was not a successor.
*
* @param oldIndex index of old successor block
* @param newIndex index of new successor block
*/
public void replaceSuccessor(int oldIndex, int newIndex) {
if (oldIndex == newIndex) {
return;
}
// Update us.
successors.set(newIndex);
if (primarySuccessor == oldIndex) {
primarySuccessor = newIndex;
}
for (int i = successorList.size() - 1 ; i >= 0; i--) {
if (successorList.get(i) == oldIndex) {
successorList.set(i, newIndex);
}
}
successors.clear(oldIndex);
// Update new successor.
parent.getBlocks().get(newIndex).predecessors.set(index);
// Update old successor.
parent.getBlocks().get(oldIndex).predecessors.clear(index);
}
/**
* Removes a successor from this block's successor list.
*
* @param oldIndex index of successor block to remove
*/
public void removeSuccessor(int oldIndex) {
int removeIndex = 0;
for (int i = successorList.size() - 1; i >= 0; i--) {
if (successorList.get(i) == oldIndex) {
removeIndex = i;
} else {
primarySuccessor = successorList.get(i);
}
}
successorList.removeIndex(removeIndex);
successors.clear(oldIndex);
parent.getBlocks().get(oldIndex).predecessors.clear(index);
}
/**
* Attaches block to an exit block if necessary. If this block
* is not an exit predecessor or is the exit block, this block does
* nothing. For use by {@link org.snapscript.dx.ssa.SsaMethod#makeExitBlock}
*
* @param exitBlock {@code non-null;} exit block
*/
public void exitBlockFixup(SsaBasicBlock exitBlock) {
if (this == exitBlock) {
return;
}
if (successorList.size() == 0) {
/*
* This is an exit predecessor.
* Set the successor to the exit block
*/
successors.set(exitBlock.index);
successorList.add(exitBlock.index);
primarySuccessor = exitBlock.index;
exitBlock.predecessors.set(this.index);
}
}
/**
* Adds a move instruction to the end of this basic block, just
* before the last instruction. If the result of the final instruction
* is the source in question, then the move is placed at the beginning of
* the primary successor block. This is for unversioned registers.
*
* @param result move destination
* @param source move source
*/
public void addMoveToEnd(RegisterSpec result, RegisterSpec source) {
if (result.getReg() == source.getReg()) {
// Sometimes we end up with no-op moves. Ignore them here.
return;
}
/*
* The last Insn has to be a normal SSA insn: a phi can't branch
* or return or cause an exception, etc.
*/
NormalSsaInsn lastInsn;
lastInsn = (NormalSsaInsn)insns.get(insns.size()-1);
if (lastInsn.getResult() != null || lastInsn.getSources().size() > 0) {
/*
* The final insn in this block has a source or result
* register, and the moves we may need to place and
* schedule may interfere. We need to insert this
* instruction at the beginning of the primary successor
* block instead. We know this is safe, because when we
* edge-split earlier, we ensured that each successor has
* only us as a predecessor.
*/
for (int i = successors.nextSetBit(0)
; i >= 0
; i = successors.nextSetBit(i + 1)) {
SsaBasicBlock succ;
succ = parent.getBlocks().get(i);
succ.addMoveToBeginning(result, source);
}
} else {
/*
* We can safely add a move to the end of the block just
* before the last instruction, because the final insn does
* not assign to anything.
*/
RegisterSpecList sources = RegisterSpecList.make(source);
NormalSsaInsn toAdd = new NormalSsaInsn(
new PlainInsn(Rops.opMove(result.getType()),
SourcePosition.NO_INFO, result, sources), this);
insns.add(insns.size() - 1, toAdd);
movesFromPhisAtEnd++;
}
}
/**
* Adds a move instruction after the phi insn block.
*
* @param result move destination
* @param source move source
*/
public void addMoveToBeginning (RegisterSpec result, RegisterSpec source) {
if (result.getReg() == source.getReg()) {
// Sometimes we end up with no-op moves. Ignore them here.
return;
}
RegisterSpecList sources = RegisterSpecList.make(source);
NormalSsaInsn toAdd = new NormalSsaInsn(
new PlainInsn(Rops.opMove(result.getType()),
SourcePosition.NO_INFO, result, sources), this);
insns.add(getCountPhiInsns(), toAdd);
movesFromPhisAtBeginning++;
}
/**
* Sets the register as used in a bitset, taking into account its
* category/width.
*
* @param regsUsed set, indexed by register number
* @param rs register to mark as used
*/
private static void setRegsUsed (BitSet regsUsed, RegisterSpec rs) {
regsUsed.set(rs.getReg());
if (rs.getCategory() > 1) {
regsUsed.set(rs.getReg() + 1);
}
}
/**
* Checks to see if the register is used in a bitset, taking
* into account its category/width.
*
* @param regsUsed set, indexed by register number
* @param rs register to mark as used
* @return true if register is fully or partially (for the case of wide
* registers) used.
*/
private static boolean checkRegUsed (BitSet regsUsed, RegisterSpec rs) {
int reg = rs.getReg();
int category = rs.getCategory();
return regsUsed.get(reg)
|| (category == 2 ? regsUsed.get(reg + 1) : false);
}
/**
* Ensures that all move operations in this block occur such that
* reads of any register happen before writes to that register.
* NOTE: caller is expected to returnSpareRegisters()!
*
* TODO: See Briggs, et al "Practical Improvements to the Construction and
* Destruction of Static Single Assignment Form" section 5. a) This can
* be done in three passes.
*
* @param toSchedule List of instructions. Must consist only of moves.
*/
private void scheduleUseBeforeAssigned(List toSchedule) {
BitSet regsUsedAsSources = new BitSet(parent.getRegCount());
// TODO: Get rid of this.
BitSet regsUsedAsResults = new BitSet(parent.getRegCount());
int sz = toSchedule.size();
int insertPlace = 0;
while (insertPlace < sz) {
int oldInsertPlace = insertPlace;
// Record all registers used as sources in this block.
for (int i = insertPlace; i < sz; i++) {
setRegsUsed(regsUsedAsSources,
toSchedule.get(i).getSources().get(0));
setRegsUsed(regsUsedAsResults,
toSchedule.get(i).getResult());
}
/*
* If there are no circular dependencies, then there exists
* n instructions where n > 1 whose result is not used as a source.
*/
for (int i = insertPlace; i
*
* This is necessary because copy-propogation may have left us in a state
* where the same basic block has the same register as a phi operand
* and a result. In this case, the register in the phi operand always
* refers value before any other phis have executed.
*/
public void scheduleMovesFromPhis() {
if (movesFromPhisAtBeginning > 1) {
List toSchedule;
toSchedule = insns.subList(0, movesFromPhisAtBeginning);
scheduleUseBeforeAssigned(toSchedule);
SsaInsn firstNonPhiMoveInsn = insns.get(movesFromPhisAtBeginning);
/*
* TODO: It's actually possible that this case never happens,
* because a move-exception block, having only one predecessor
* in SSA form, perhaps is never on a dominance frontier.
*/
if (firstNonPhiMoveInsn.isMoveException()) {
if (true) {
/*
* We've yet to observe this case, and if it can
* occur the code written to handle it probably
* does not work.
*/
throw new RuntimeException(
"Unexpected: moves from "
+"phis before move-exception");
} else {
/*
* A move-exception insn must be placed first in this block
* We need to move it there, and deal with possible
* interference.
*/
boolean moveExceptionInterferes = false;
int moveExceptionResult
= firstNonPhiMoveInsn.getResult().getReg();
/*
* Does the move-exception result reg interfere with the
* phi moves?
*/
for (SsaInsn insn : toSchedule) {
if (insn.isResultReg(moveExceptionResult)
|| insn.isRegASource(moveExceptionResult)) {
moveExceptionInterferes = true;
break;
}
}
if (!moveExceptionInterferes) {
// This is the easy case.
insns.remove(movesFromPhisAtBeginning);
insns.add(0, firstNonPhiMoveInsn);
} else {
/*
* We need to move the result to a spare reg
* and move it back.
*/
RegisterSpec originalResultSpec
= firstNonPhiMoveInsn.getResult();
int spareRegister = parent.borrowSpareRegister(
originalResultSpec.getCategory());
// We now move it to a spare register.
firstNonPhiMoveInsn.changeResultReg(spareRegister);
RegisterSpec tempSpec =
firstNonPhiMoveInsn.getResult();
insns.add(0, firstNonPhiMoveInsn);
// And here we move it back.
NormalSsaInsn toAdd = new NormalSsaInsn(
new PlainInsn(
Rops.opMove(tempSpec.getType()),
SourcePosition.NO_INFO,
originalResultSpec,
RegisterSpecList.make(tempSpec)),
this);
/*
* Place it immediately after the phi-moves,
* overwriting the move-exception that was there.
*/
insns.set(movesFromPhisAtBeginning + 1, toAdd);
}
}
}
}
if (movesFromPhisAtEnd > 1) {
scheduleUseBeforeAssigned(
insns.subList(insns.size() - movesFromPhisAtEnd - 1,
insns.size() - 1));
}
// Return registers borrowed here and in scheduleUseBeforeAssigned().
parent.returnSpareRegisters();
}
/**
* Visits all insns in this block.
*
* @param visitor {@code non-null;} callback interface
*/
public void forEachInsn(SsaInsn.Visitor visitor) {
// This gets called a LOT, and not using an iterator
// saves a lot of allocations and reduces memory usage
int len = insns.size();
for (int i = 0; i < len; i++) {
insns.get(i).accept(visitor);
}
}
/** {@inheritDoc} */
@Override
public String toString() {
return "{" + index + ":" + Hex.u2(ropLabel) + '}';
}
/**
* Visitor interface for basic blocks.
*/
public interface Visitor {
/**
* Indicates a block has been visited by an iterator method.
*
* @param v {@code non-null;} block visited
* @param parent {@code null-ok;} parent node if applicable
*/
void visitBlock (SsaBasicBlock v, SsaBasicBlock parent);
}
/**
* Label comparator.
*/
public static final class LabelComparator
implements Comparator {
/** {@inheritDoc} */
public int compare(SsaBasicBlock b1, SsaBasicBlock b2) {
int label1 = b1.ropLabel;
int label2 = b2.ropLabel;
if (label1 < label2) {
return -1;
} else if (label1 > label2) {
return 1;
} else {
return 0;
}
}
}
}
