/** Eliminate instructions that are not reached */
boolean eliminate() {
boolean change = false;
Instruction prev = first;
for (Instruction inst = first.next; inst != null; inst = inst.next) {
if (inst.pc != NOTREACHED) {
prev.next = inst;
prev = inst;
inst.pc = NOTREACHED;
} else {
change = true;
}
}
first.pc = NOTREACHED;
prev.next = null;
return change;
}
/** Optimize instructions and mark those that can be reached */
void optimize(Environment env, Label lbl) {
lbl.pc = REACHED;
for (Instruction inst = lbl.next; inst != null; inst = inst.next) {
switch (inst.pc) {
case NOTREACHED:
inst.optimize(env);
inst.pc = REACHED;
break;
case REACHED:
return;
case NEEDED:
break;
}
switch (inst.opc) {
case opc_label:
case opc_dead:
if (inst.pc == REACHED) {
inst.pc = NOTREACHED;
}
break;
case opc_ifeq:
case opc_ifne:
case opc_ifgt:
case opc_ifge:
case opc_iflt:
case opc_ifle:
case opc_if_icmpeq:
case opc_if_icmpne:
case opc_if_icmpgt:
case opc_if_icmpge:
case opc_if_icmplt:
case opc_if_icmple:
case opc_if_acmpeq:
case opc_if_acmpne:
case opc_ifnull:
case opc_ifnonnull:
optimize(env, (Label) inst.value);
break;
case opc_goto:
optimize(env, (Label) inst.value);
return;
case opc_jsr:
optimize(env, (Label) inst.value);
break;
case opc_ret:
case opc_return:
case opc_ireturn:
case opc_lreturn:
case opc_freturn:
case opc_dreturn:
case opc_areturn:
case opc_athrow:
return;
case opc_tableswitch:
case opc_lookupswitch:
{
SwitchData sw = (SwitchData) inst.value;
optimize(env, sw.defaultLabel);
for (Enumeration e = sw.tab.elements(); e.hasMoreElements(); ) {
optimize(env, (Label) e.nextElement());
}
return;
}
case opc_try:
{
TryData td = (TryData) inst.value;
td.getEndLabel().pc = NEEDED;
for (Enumeration e = td.catches.elements(); e.hasMoreElements(); ) {
CatchData cd = (CatchData) e.nextElement();
optimize(env, cd.getLabel());
}
break;
}
}
}
}
/**
* Figure out when registers contain a legal value. This is done using a simple data flow
* algorithm. This information is later used to generate the local variable table.
*/
void flowFields(Environment env, Label lbl, MemberDefinition locals[]) {
if (lbl.locals != null) {
// Been here before. Erase any conflicts.
MemberDefinition f[] = lbl.locals;
for (int i = 0; i < maxvar; i++) {
if (f[i] != locals[i]) {
f[i] = null;
}
}
return;
}
// Remember the set of active registers at this point
lbl.locals = new MemberDefinition[maxvar];
System.arraycopy(locals, 0, lbl.locals, 0, maxvar);
MemberDefinition newlocals[] = new MemberDefinition[maxvar];
System.arraycopy(locals, 0, newlocals, 0, maxvar);
locals = newlocals;
for (Instruction inst = lbl.next; inst != null; inst = inst.next) {
switch (inst.opc) {
case opc_istore:
case opc_istore_0:
case opc_istore_1:
case opc_istore_2:
case opc_istore_3:
case opc_fstore:
case opc_fstore_0:
case opc_fstore_1:
case opc_fstore_2:
case opc_fstore_3:
case opc_astore:
case opc_astore_0:
case opc_astore_1:
case opc_astore_2:
case opc_astore_3:
case opc_lstore:
case opc_lstore_0:
case opc_lstore_1:
case opc_lstore_2:
case opc_lstore_3:
case opc_dstore:
case opc_dstore_0:
case opc_dstore_1:
case opc_dstore_2:
case opc_dstore_3:
if (inst.value instanceof LocalVariable) {
LocalVariable v = (LocalVariable) inst.value;
locals[v.slot] = v.field;
}
break;
case opc_label:
flowFields(env, (Label) inst, locals);
return;
case opc_ifeq:
case opc_ifne:
case opc_ifgt:
case opc_ifge:
case opc_iflt:
case opc_ifle:
case opc_if_icmpeq:
case opc_if_icmpne:
case opc_if_icmpgt:
case opc_if_icmpge:
case opc_if_icmplt:
case opc_if_icmple:
case opc_if_acmpeq:
case opc_if_acmpne:
case opc_ifnull:
case opc_ifnonnull:
case opc_jsr:
flowFields(env, (Label) inst.value, locals);
break;
case opc_goto:
flowFields(env, (Label) inst.value, locals);
return;
case opc_return:
case opc_ireturn:
case opc_lreturn:
case opc_freturn:
case opc_dreturn:
case opc_areturn:
case opc_athrow:
case opc_ret:
return;
case opc_tableswitch:
case opc_lookupswitch:
{
SwitchData sw = (SwitchData) inst.value;
flowFields(env, sw.defaultLabel, locals);
for (Enumeration e = sw.tab.elements(); e.hasMoreElements(); ) {
flowFields(env, (Label) e.nextElement(), locals);
}
return;
}
case opc_try:
{
Vector catches = ((TryData) inst.value).catches;
for (Enumeration e = catches.elements(); e.hasMoreElements(); ) {
CatchData cd = (CatchData) e.nextElement();
flowFields(env, cd.getLabel(), locals);
}
break;
}
}
}
}
/** Determine stack size, count local variables */
void balance(Label lbl, int depth) {
for (Instruction inst = lbl; inst != null; inst = inst.next) {
// Environment.debugOutput(inst.toString() + ": " + depth + " => " +
// (depth + inst.balance()));
depth += inst.balance();
if (depth < 0) {
throw new CompilerError("stack under flow: " + inst.toString() + " = " + depth);
}
if (depth > maxdepth) {
maxdepth = depth;
}
switch (inst.opc) {
case opc_label:
lbl = (Label) inst;
if (inst.pc == REACHED) {
if (lbl.depth != depth) {
throw new CompilerError(
"stack depth error " + depth + "/" + lbl.depth + ": " + inst.toString());
}
return;
}
lbl.pc = REACHED;
lbl.depth = depth;
break;
case opc_ifeq:
case opc_ifne:
case opc_ifgt:
case opc_ifge:
case opc_iflt:
case opc_ifle:
case opc_if_icmpeq:
case opc_if_icmpne:
case opc_if_icmpgt:
case opc_if_icmpge:
case opc_if_icmplt:
case opc_if_icmple:
case opc_if_acmpeq:
case opc_if_acmpne:
case opc_ifnull:
case opc_ifnonnull:
balance((Label) inst.value, depth);
break;
case opc_goto:
balance((Label) inst.value, depth);
return;
case opc_jsr:
balance((Label) inst.value, depth + 1);
break;
case opc_ret:
case opc_return:
case opc_ireturn:
case opc_lreturn:
case opc_freturn:
case opc_dreturn:
case opc_areturn:
case opc_athrow:
return;
case opc_iload:
case opc_fload:
case opc_aload:
case opc_istore:
case opc_fstore:
case opc_astore:
{
int v =
((inst.value instanceof Number)
? ((Number) inst.value).intValue()
: ((LocalVariable) inst.value).slot)
+ 1;
if (v > maxvar) maxvar = v;
break;
}
case opc_lload:
case opc_dload:
case opc_lstore:
case opc_dstore:
{
int v =
((inst.value instanceof Number)
? ((Number) inst.value).intValue()
: ((LocalVariable) inst.value).slot)
+ 2;
if (v > maxvar) maxvar = v;
break;
}
case opc_iinc:
{
int v = ((int[]) inst.value)[0] + 1;
if (v > maxvar) maxvar = v + 1;
break;
}
case opc_tableswitch:
case opc_lookupswitch:
{
SwitchData sw = (SwitchData) inst.value;
balance(sw.defaultLabel, depth);
for (Enumeration e = sw.tab.elements(); e.hasMoreElements(); ) {
balance((Label) e.nextElement(), depth);
}
return;
}
case opc_try:
{
TryData td = (TryData) inst.value;
for (Enumeration e = td.catches.elements(); e.hasMoreElements(); ) {
CatchData cd = (CatchData) e.nextElement();
balance(cd.getLabel(), depth + 1);
}
break;
}
}
}
}