/**
* Inserts mark-locals if necessary when changing a register. If the definition of {@code origReg}
* is associated with a local variable, then insert a mark-local for {@code newReg} just below it.
* We expect the definition of {@code origReg} to ultimately be removed by the dead code
* eliminator
*
* @param origReg {@code non-null;} original register
* @param newReg {@code non-null;} new register that will replace {@code origReg}
*/
private void fixLocalAssignment(RegisterSpec origReg, RegisterSpec newReg) {
for (SsaInsn use : ssaMeth.getUseListForRegister(origReg.getReg())) {
RegisterSpec localAssignment = use.getLocalAssignment();
if (localAssignment == null) {
continue;
}
if (use.getResult() == null) {
/*
* This is a mark-local. it will be updated when all uses are
* updated.
*/
continue;
}
LocalItem local = localAssignment.getLocalItem();
// Un-associate original use.
use.setResultLocal(null);
// Now add a mark-local to the new reg immediately after.
newReg = newReg.withLocalItem(local);
SsaInsn newInsn =
SsaInsn.makeFromRop(
new PlainInsn(
Rops.opMarkLocal(newReg),
SourcePosition.NO_INFO,
null,
RegisterSpecList.make(newReg)),
use.getBlock());
ArrayList<SsaInsn> insns = use.getBlock().getInsns();
insns.add(insns.indexOf(use) + 1, newInsn);
}
}
/**
* Processes a single block.
*
* @param blockIndex {@code >= 0;} block index of the block to process
*/
private void processBlock(int blockIndex) {
RegisterSpecSet primaryState = resultInfo.mutableCopyOfStarts(blockIndex);
SsaBasicBlock block = blocks.get(blockIndex);
List<SsaInsn> insns = block.getInsns();
int insnSz = insns.size();
// The exit block has no insns and no successors
if (blockIndex == method.getExitBlockIndex()) {
return;
}
/*
* We may have to treat the last instruction specially: If it
* can (but doesn't always) throw, and the exception can be
* caught within the same method, then we need to use the
* state *before* executing it to be what is merged into
* exception targets.
*/
SsaInsn lastInsn = insns.get(insnSz - 1);
boolean hasExceptionHandlers = lastInsn.getOriginalRopInsn().getCatches().size() != 0;
boolean canThrowDuringLastInsn = hasExceptionHandlers && (lastInsn.getResult() != null);
int freezeSecondaryStateAt = insnSz - 1;
RegisterSpecSet secondaryState = primaryState;
/*
* Iterate over the instructions, adding information for each place
* that the active variable set changes.
*/
for (int i = 0; i < insnSz; i++) {
if (canThrowDuringLastInsn && (i == freezeSecondaryStateAt)) {
// Until this point, primaryState == secondaryState.
primaryState.setImmutable();
primaryState = primaryState.mutableCopy();
}
SsaInsn insn = insns.get(i);
RegisterSpec result;
result = insn.getLocalAssignment();
if (result == null) {
// We may be nuking an existing local
result = insn.getResult();
if (result != null && primaryState.get(result.getReg()) != null) {
primaryState.remove(primaryState.get(result.getReg()));
}
continue;
}
result = result.withSimpleType();
RegisterSpec already = primaryState.get(result);
/*
* The equals() check ensures we only add new info if
* the instruction causes a change to the set of
* active variables.
*/
if (!result.equals(already)) {
/*
* If this insn represents a local moving from one register
* to another, remove the association between the old register
* and the local.
*/
RegisterSpec previous = primaryState.localItemToSpec(result.getLocalItem());
if (previous != null && (previous.getReg() != result.getReg())) {
primaryState.remove(previous);
}
resultInfo.addAssignment(insn, result);
primaryState.put(result);
}
}
primaryState.setImmutable();
/*
* Merge this state into the start state for each successor,
* and update the work set where required (that is, in cases
* where the start state for a block changes).
*/
IntList successors = block.getSuccessorList();
int succSz = successors.size();
int primarySuccessor = block.getPrimarySuccessorIndex();
for (int i = 0; i < succSz; i++) {
int succ = successors.get(i);
RegisterSpecSet state = (succ == primarySuccessor) ? primaryState : secondaryState;
if (resultInfo.mergeStarts(succ, state)) {
workSet.set(succ);
}
}
}
/**
* Sorts move instructions added via {@code addMoveToEnd} during phi removal so that results don't
* overwrite sources that are used. For use after all phis have been removed and all calls to
* addMoveToEnd() have been made.
*
* <p>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<SsaInsn> 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();
}
/**
* 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<SsaInsn> 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 < sz; i++) {
SsaInsn insn = toSchedule.get(i);
/*
* Move these n registers to the front, since they overwrite
* nothing.
*/
if (!checkRegUsed(regsUsedAsSources, insn.getResult())) {
Collections.swap(toSchedule, i, insertPlace++);
}
}
/*
* If we've made no progress in this iteration, there's a circular
* dependency. Split it using the temp reg.
*/
if (oldInsertPlace == insertPlace) {
SsaInsn insnToSplit = null;
// Find an insn whose result is used as a source.
for (int i = insertPlace; i < sz; i++) {
SsaInsn insn = toSchedule.get(i);
if (checkRegUsed(regsUsedAsSources, insn.getResult())
&& checkRegUsed(regsUsedAsResults, insn.getSources().get(0))) {
insnToSplit = insn;
/*
* We're going to split this insn; move it to the front.
*/
Collections.swap(toSchedule, insertPlace, i);
break;
}
}
// At least one insn will be set above.
RegisterSpec result = insnToSplit.getResult();
RegisterSpec tempSpec = result.withReg(parent.borrowSpareRegister(result.getCategory()));
NormalSsaInsn toAdd =
new NormalSsaInsn(
new PlainInsn(
Rops.opMove(result.getType()),
SourcePosition.NO_INFO,
tempSpec,
insnToSplit.getSources()),
this);
toSchedule.add(insertPlace++, toAdd);
RegisterSpecList newSources = RegisterSpecList.make(tempSpec);
NormalSsaInsn toReplace =
new NormalSsaInsn(
new PlainInsn(
Rops.opMove(result.getType()), SourcePosition.NO_INFO, result, newSources),
this);
toSchedule.set(insertPlace, toReplace);
// The size changed.
sz = toSchedule.size();
}
regsUsedAsSources.clear();
regsUsedAsResults.clear();
}
}
/**
* Updates all uses of various consts to use the values in the newly assigned registers.
*
* @param newRegs {@code non-null;} mapping between constant and new reg
* @param origRegCount {@code >=0;} original SSA reg count, not including newly added constant
* regs
*/
private void updateConstUses(HashMap<TypedConstant, RegisterSpec> newRegs, int origRegCount) {
/*
* set of constants associated with a local variable; used only if
* COLLECT_ONE_LOCAL is true.
*/
final HashSet<TypedConstant> usedByLocal = new HashSet<TypedConstant>();
final ArrayList<SsaInsn>[] useList = ssaMeth.getUseListCopy();
for (int i = 0; i < origRegCount; i++) {
SsaInsn insn = ssaMeth.getDefinitionForRegister(i);
if (insn == null) {
continue;
}
final RegisterSpec origReg = insn.getResult();
TypeBearer typeBearer = insn.getResult().getTypeBearer();
if (!typeBearer.isConstant()) continue;
TypedConstant cst = (TypedConstant) typeBearer;
final RegisterSpec newReg = newRegs.get(cst);
if (newReg == null) {
continue;
}
if (ssaMeth.isRegALocal(origReg)) {
if (!COLLECT_ONE_LOCAL) {
continue;
} else {
/*
* TODO: If the same local gets the same cst multiple times,
* it would be nice to reuse the register.
*/
if (usedByLocal.contains(cst)) {
continue;
} else {
usedByLocal.add(cst);
fixLocalAssignment(origReg, newRegs.get(cst));
}
}
}
// maps an original const register to the new collected register
RegisterMapper mapper =
new RegisterMapper() {
@Override
public int getNewRegisterCount() {
return ssaMeth.getRegCount();
}
@Override
public RegisterSpec map(RegisterSpec registerSpec) {
if (registerSpec.getReg() == origReg.getReg()) {
return newReg.withLocalItem(registerSpec.getLocalItem());
}
return registerSpec;
}
};
for (SsaInsn use : useList[origReg.getReg()]) {
if (use.canThrow() && use.getBlock().getSuccessors().cardinality() > 1) {
continue;
}
use.mapSourceRegisters(mapper);
}
}
}
/**
* Gets all of the collectable constant values used in this method, sorted by most used first.
* Skips non-collectable consts, such as non-string object constants
*
* @return {@code non-null;} list of constants in most-to-least used order
*/
private ArrayList<TypedConstant> getConstsSortedByCountUse() {
int regSz = ssaMeth.getRegCount();
final HashMap<TypedConstant, Integer> countUses = new HashMap<TypedConstant, Integer>();
/*
* Each collected constant can be used by just one local (used only if
* COLLECT_ONE_LOCAL is true).
*/
final HashSet<TypedConstant> usedByLocal = new HashSet<TypedConstant>();
// Count how many times each const value is used.
for (int i = 0; i < regSz; i++) {
SsaInsn insn = ssaMeth.getDefinitionForRegister(i);
if (insn == null || insn.getOpcode() == null) continue;
RegisterSpec result = insn.getResult();
TypeBearer typeBearer = result.getTypeBearer();
if (!typeBearer.isConstant()) continue;
TypedConstant cst = (TypedConstant) typeBearer;
// Find defining instruction for move-result-pseudo instructions
if (insn.getOpcode().getOpcode() == RegOps.MOVE_RESULT_PSEUDO) {
int pred = insn.getBlock().getPredecessors().nextSetBit(0);
ArrayList<SsaInsn> predInsns;
predInsns = ssaMeth.getBlocks().get(pred).getInsns();
insn = predInsns.get(predInsns.size() - 1);
}
if (insn.canThrow()) {
/*
* Don't move anything other than strings -- the risk of
* changing where an exception is thrown is too high.
*/
if (!(cst instanceof CstString) || !COLLECT_STRINGS) {
continue;
}
/*
* We can't move any throwable const whose throw will be caught,
* so don't count them.
*/
if (insn.getBlock().getSuccessors().cardinality() > 1) {
continue;
}
}
/*
* TODO: Might be nice to try and figure out which local wins most
* when collected.
*/
if (ssaMeth.isRegALocal(result)) {
if (!COLLECT_ONE_LOCAL) {
continue;
} else {
if (usedByLocal.contains(cst)) {
// Count one local usage only.
continue;
} else {
usedByLocal.add(cst);
}
}
}
Integer has = countUses.get(cst);
if (has == null) {
countUses.put(cst, 1);
} else {
countUses.put(cst, has + 1);
}
}
// Collect constants that have been reused.
ArrayList<TypedConstant> constantList = new ArrayList<TypedConstant>();
for (Map.Entry<TypedConstant, Integer> entry : countUses.entrySet()) {
if (entry.getValue() > 1) {
constantList.add(entry.getKey());
}
}
// Sort by use, with most used at the beginning of the list.
Collections.sort(
constantList,
new Comparator<Constant>() {
public int compare(Constant a, Constant b) {
int ret;
ret = countUses.get(b) - countUses.get(a);
if (ret == 0) {
/*
* Provide sorting determinisim for constants with same
* usage count.
*/
ret = a.compareTo(b);
}
return ret;
}
@Override
public boolean equals(Object obj) {
return obj == this;
}
});
return constantList;
}