/**
* Transform to eliminate redundant branches passed on GVNs and dominator information.
*
* @param ir The IR on which to apply the phase
*/
public void perform(IR ir) {
// (1) Remove redundant conditional branches and locally fix the PHIs
GlobalValueNumberState gvns = ir.HIRInfo.valueNumbers;
DominatorTree dt = ir.HIRInfo.dominatorTree;
for (BasicBlockEnumeration bbs = ir.getBasicBlocks(); bbs.hasMoreElements(); ) {
BasicBlock candBB = bbs.next();
Instruction candTest = candBB.firstBranchInstruction();
if (candTest == null) continue;
if (!(IfCmp.conforms(candTest) || InlineGuard.conforms(candTest))) continue;
GVCongruenceClass cc = gvns.congruenceClass(candTest);
if (cc.size() > 1) {
for (ValueGraphVertex vertex : cc) {
Instruction poss = (Instruction) vertex.getName();
if (poss != candTest) {
BasicBlock notTaken = getNotTakenBlock(poss);
BasicBlock taken = poss.getBranchTarget();
if (taken == notTaken) continue; // both go to same block, so we don't know anything!
if (notTaken.hasOneIn() && dt.dominates(notTaken, candBB)) {
if (DEBUG)
VM.sysWrite(candTest + " is dominated by not-taken branch of " + poss + "\n");
removeCondBranch(candBB, candTest, ir, poss);
cc.removeVertex(gvns.valueGraph.getVertex(candTest));
break;
}
if (taken.hasOneIn() && dt.dominates(taken, candBB)) {
if (DEBUG)
VM.sysWrite(candTest + " is dominated by taken branch of " + poss + "\n");
takeCondBranch(candBB, candTest, ir);
cc.removeVertex(gvns.valueGraph.getVertex(candTest));
break;
}
}
}
}
}
// (2) perform a Depth-first search of the control flow graph,
// and remove any nodes we have made unreachable
removeUnreachableCode(ir);
}
/**
* Do a quick pass over the IR, and return types that are candidates for redundant load
* elimination. Algorithm: return those types T where 1) there's a load L(i) of type T 2) there's
* another load or store M(j) of type T, M!=L and V(i) == V(j)
*
* <p>The result contains objects of type RVMField and TypeReference, whose narrowest common
* ancestor is Object.
*/
@SuppressWarnings("unchecked")
public static HashSet<Object> getCandidates(IR ir) {
GlobalValueNumberState valueNumbers = ir.HIRInfo.valueNumbers;
// which types have we seen loads for?
HashSet<Object> seenLoad = new HashSet<Object>(10);
// which static fields have we seen stores for?
HashSet<RVMField> seenStore = new HashSet<RVMField>(10);
HashSet<Object> resultSet = new HashSet<Object>(10);
HashSet<FieldReference> forbidden = new HashSet<FieldReference>(10);
// for each type T, indices(T) gives the set of value number (pairs)
// that identify the indices seen in memory accesses to type T.
HashMap indices = new HashMap(10);
for (Enumeration be = ir.getBasicBlocks(); be.hasMoreElements(); ) {
BasicBlock bb = (BasicBlock) be.nextElement();
if (!ir.options.FREQ_FOCUS_EFFORT || !bb.getInfrequent()) {
for (InstructionEnumeration e = bb.forwardInstrEnumerator(); e.hasMoreElements(); ) {
Instruction s = e.next();
switch (s.operator().opcode) {
case GETFIELD_opcode:
{
Operand ref = GetField.getRef(s);
FieldReference fr = GetField.getLocation(s).getFieldRef();
RVMField f = fr.peekResolvedField();
if (f == null) {
forbidden.add(fr);
} else {
HashSet<Integer> numbers = findOrCreateIndexSet(indices, f);
int v = valueNumbers.getValueNumber(ref);
Integer V = v;
if (numbers.contains(V)) {
resultSet.add(f);
} else {
numbers.add(V);
}
seenLoad.add(f);
}
}
break;
case PUTFIELD_opcode:
{
Operand ref = PutField.getRef(s);
FieldReference fr = PutField.getLocation(s).getFieldRef();
RVMField f = fr.peekResolvedField();
if (f == null) {
forbidden.add(fr);
} else {
HashSet<Integer> numbers = findOrCreateIndexSet(indices, f);
int v = valueNumbers.getValueNumber(ref);
Integer V = v;
if (numbers.contains(V)) {
if (seenLoad.contains(f)) {
resultSet.add(f);
}
} else {
numbers.add(V);
}
}
}
break;
case GETSTATIC_opcode:
{
FieldReference fr = GetStatic.getLocation(s).getFieldRef();
RVMField f = fr.peekResolvedField();
if (f == null) {
forbidden.add(fr);
} else {
if (seenLoad.contains(f) || seenStore.contains(f)) {
resultSet.add(f);
}
seenLoad.add(f);
}
}
break;
case PUTSTATIC_opcode:
{
FieldReference fr = PutStatic.getLocation(s).getFieldRef();
RVMField f = fr.peekResolvedField();
if (f == null) {
forbidden.add(fr);
} else {
if (seenLoad.contains(f)) {
resultSet.add(f);
}
seenStore.add(f);
}
}
break;
case INT_ALOAD_opcode:
case LONG_ALOAD_opcode:
case FLOAT_ALOAD_opcode:
case DOUBLE_ALOAD_opcode:
case REF_ALOAD_opcode:
case BYTE_ALOAD_opcode:
case UBYTE_ALOAD_opcode:
case USHORT_ALOAD_opcode:
case SHORT_ALOAD_opcode:
{
Operand ref = ALoad.getArray(s);
TypeReference type = ref.getType();
if (type.isArrayType()) {
if (!type.getArrayElementType().isPrimitiveType()) {
type = TypeReference.JavaLangObjectArray;
}
}
Operand index = ALoad.getIndex(s);
HashSet<ValueNumberPair> numbers = findOrCreateIndexSet(indices, type);
int v1 = valueNumbers.getValueNumber(ref);
int v2 = valueNumbers.getValueNumber(index);
ValueNumberPair V = new ValueNumberPair(v1, v2);
if (numbers.contains(V)) {
resultSet.add(type);
} else {
numbers.add(V);
}
seenLoad.add(type);
}
break;
case INT_ASTORE_opcode:
case LONG_ASTORE_opcode:
case FLOAT_ASTORE_opcode:
case DOUBLE_ASTORE_opcode:
case REF_ASTORE_opcode:
case BYTE_ASTORE_opcode:
case SHORT_ASTORE_opcode:
{
Operand ref = AStore.getArray(s);
TypeReference type = ref.getType();
if (type.isArrayType()) {
if (!type.getArrayElementType().isPrimitiveType()) {
type = TypeReference.JavaLangObjectArray;
}
}
Operand index = AStore.getIndex(s);
HashSet<ValueNumberPair> numbers = findOrCreateIndexSet(indices, type);
int v1 = valueNumbers.getValueNumber(ref);
int v2 = valueNumbers.getValueNumber(index);
ValueNumberPair V = new ValueNumberPair(v1, v2);
if (numbers.contains(V)) {
if (seenLoad.contains(type)) {
resultSet.add(type);
}
} else {
numbers.add(V);
}
}
break;
default:
break;
}
}
}
}
// If we have found an unresolved field reference, then conservatively
// remove all fields that it might refer to from the resultSet.
for (final FieldReference fieldReference : forbidden) {
for (Iterator i2 = resultSet.iterator(); i2.hasNext(); ) {
Object it = i2.next();
if (it instanceof RVMField) {
final RVMField field = (RVMField) it;
if (!fieldReference.definitelyDifferent(field.getMemberRef().asFieldReference())) {
i2.remove();
}
}
}
}
return resultSet;
}
/**
* Walk over each instruction. If its a USE (load) of a heap variable and the value is available,
* then replace the load with a move from a register.
*
* <p>POSTCONDITION: sets up the mapping 'registers' from value number to temporary register
*
* @param ir the IR
* @param available information on which values are available
* @param registers a place to store information about temp registers
*/
static UseRecordSet replaceLoads(
IR ir, DF_Solution available, HashMap<UseRecord, Register> registers) {
UseRecordSet result = new UseRecordSet();
SSADictionary ssa = ir.HIRInfo.dictionary;
GlobalValueNumberState valueNumbers = ir.HIRInfo.valueNumbers;
for (Enumeration<Instruction> e = ir.forwardInstrEnumerator(); e.hasMoreElements(); ) {
Instruction s = e.nextElement();
if (!GetField.conforms(s) && !GetStatic.conforms(s) && !ALoad.conforms(s)) {
continue;
}
// this instruction is a USE of heap variable H.
// get the lattice cell that holds the available indices
// for this heap variable
HeapOperand<?>[] H = ssa.getHeapUses(s);
if (H == null) {
// this case can happen due to certain magics that insert
// INT_LOAD instructions in HIR
// TODO: clean up HIR representation of these magics
continue;
}
if (H.length != 1) {
throw new OptimizingCompilerException(
"LoadElimination: load with wrong number of heap uses");
}
if (GetField.conforms(s) || GetStatic.conforms(s)) {
int valueNumber = -1;
if (GetField.conforms(s)) {
Object address = GetField.getRef(s);
valueNumber = valueNumbers.getValueNumber(address);
} else {
// for getStatic, always use the value number 0
valueNumber = 0;
}
ObjectCell cell = (ObjectCell) available.lookup(H[0].getHeapVariable());
if (cell == null) {
continue; // nothing available
}
// .. if H{valueNumber} is available ...
if (cell.contains(valueNumber)) {
result.add(H[0].getHeapVariable(), valueNumber);
TypeReference type = ResultCarrier.getResult(s).getType();
Register r =
findOrCreateRegister(H[0].getHeapType(), valueNumber, registers, ir.regpool, type);
if (DEBUG) {
System.out.println("ELIMINATING LOAD " + s);
}
replaceLoadWithMove(r, s);
}
} else { // ALoad.conforms(s)
Object array = ALoad.getArray(s);
Object index = ALoad.getIndex(s);
ArrayCell cell = (ArrayCell) available.lookup(H[0].getHeapVariable());
if (cell == null) {
continue; // nothing available
}
int v1 = valueNumbers.getValueNumber(array);
int v2 = valueNumbers.getValueNumber(index);
// .. if H{<v1,v2>} is available ...
if (cell.contains(v1, v2)) {
result.add(H[0].getHeapVariable(), v1, v2);
TypeReference type = ALoad.getResult(s).getType();
Register r =
findOrCreateRegister(
H[0].getHeapVariable().getHeapType(), v1, v2, registers, ir.regpool, type);
if (DEBUG) {
System.out.println("ELIMINATING LOAD " + s);
}
replaceLoadWithMove(r, s);
}
}
}
return result;
}
