openrs2
/
jode
0
0
Fork 0
Code Issues 1 Pull Requests Releases Wiki Activity

dead code elimination

Browse Source 
print all flow blocks


git-svn-id: https://svn.code.sf.net/p/jode/code/trunk@205 379699f6-c40d-0410-875b-85095c16579e
stable
jochen 26 years ago
parent cf1ef397e5
commit acfe14f7af
1 changed files with 205 additions and 44 deletions
Show all changes Ignore whitespace when comparing lines Ignore changes in amount of whitespace Ignore changes in whitespace at EOL
Show Stats Download Patch File Download Diff File
  1. 245
      jode/jode/flow/FlowBlock.java

245
jode/jode/flow/FlowBlock.java
Unescape View File

@ -37,6 +37,9 @@ public class FlowBlock {
static FlowBlock END_OF_METHOD =
new FlowBlock(null, Integer.MAX_VALUE, 0, new EmptyBlock());
static FlowBlock ILLEGAL =
new FlowBlock(null, -1, 0, new DescriptionBlock("ILLEGAL BLOCK"));
static {
END_OF_METHOD.label = "END_OF_METHOD";
}
@ -88,7 +91,7 @@ public class FlowBlock {
/**
* This contains a map of all successing flow blocks and there
* jumps. The key of this dictionary are the flow blocks, while
* the elements is the first jump to that dictionary. The other
* the elements is the first jump to that flow block. The other
* jumps are accessible via the jump.next field.
*/
Dictionary successors = new SimpleDictionary();
@ -103,6 +106,25 @@ public class FlowBlock {
*/
Vector predecessors = new Vector();
/**
* This is set if the block is reachable. If this is false after
* marking the start block and the catch blocks as reachable, this
* block is dead code and may (must) be removed.
*/
boolean reachable = false;
/**
* This is a pointer to the next flow block in byte code order.
* It is null for the last flow block.
*/
FlowBlock nextByAddr;
/**
* This is a pointer to the previous flow block in byte code order.
* It is null for the first flow block.
*/
FlowBlock prevByAddr;
/**
* The default constructor. Creates a new flowblock containing
* only the given structured block.
@ -118,7 +140,7 @@ public class FlowBlock {
block.fillInGenSet(in, gen);
}
public int getNextAddr() {
public final int getNextAddr() {
return addr+length;
}
@ -168,20 +190,17 @@ public class FlowBlock {
* be lastModified.
*/
/* remove this jump if it jumps to the getNextFlowBlock().
*/
if (jump.destination
== jump.prev.outer.getNextFlowBlock(jump.prev)) {
jump.prev.removeJump();
continue;
}
if (jump.prev.outer instanceof ConditionalBlock) {
StructuredBlock prev = jump.prev;
ConditionalBlock cb = (ConditionalBlock) prev.outer;
Expression instr = cb.getInstruction();
/* This is a jump inside an ConditionalBlock.
*
* cb is the conditional block,
* prev the empty block containing the jump
* instr is the condition */
if (cb.jump != null) {
/* This can only happen if cb also jumps to succ.
* This is a weired "if (cond) empty"-block. We
@ -189,26 +208,29 @@ public class FlowBlock {
*/
prev.removeJump();
IfThenElseBlock ifBlock =
new IfThenElseBlock(cb.getInstruction());
new IfThenElseBlock(cb.getInstruction().negate());
ifBlock.moveDefinitions(cb, prev);
ifBlock.replace(cb);
ifBlock.moveJump(cb.jump);
ifBlock.setThenBlock(prev);
if (cb == lastModified)
lastModified = ifBlock;
continue;
}
/* Now cb.jump is null, so cb.outer is not null,
* since otherwise it would have no successor. */
/* If this is the first instruction of a
* while/for(true) block, make this the loop condition
* (negated of course).
*/
if (cb.outer instanceof LoopBlock
|| (cb.outer instanceof SequentialBlock
&& cb.outer.getSubBlocks()[0] == cb
&& cb.outer.outer instanceof LoopBlock)) {
/* If this is the first instruction of a
* while/for(true) block, make this the loop condition
* (negated of course).
*/
LoopBlock loopBlock = (cb.outer instanceof LoopBlock) ?
(LoopBlock) cb.outer : (LoopBlock) cb.outer.outer;
@ -268,9 +290,19 @@ public class FlowBlock {
}
}
/* This is still a jump inside an ConditionalBlock.
*
* cb is the conditional block,
* prev the empty block containing the jump
* instr is the condition */
/* replace all conditional jumps to the successor, which
* are followed by a block which has the end of the block
* as normal successor, with "if (not condition) block".
* as normal successor, with "if (not condition) block":
*
* /IF cond GOTO succ if (!cond)
* \block ===> block
* -> normal Succesor succ -> normal Successor succ
*/
if (cb.outer instanceof SequentialBlock &&
cb.outer.getSubBlocks()[0] == cb &&
@ -304,6 +336,15 @@ public class FlowBlock {
}
} else {
/* remove this jump if it jumps to the
* getNextFlowBlock(). */
if (jump.destination
== jump.prev.outer.getNextFlowBlock(jump.prev)) {
jump.prev.removeJump();
continue;
}
/* Now find the real outer block, that is ascend the chain
* of SequentialBlocks.
*
@ -317,11 +358,31 @@ public class FlowBlock {
while (sb instanceof SequentialBlock)
sb = sb.outer;
/* if this is a unconditional jump at the end of a
* then block belonging to a if-then block without
* else part, but a single jump, then replace the
* if-then block with a if-then-else block with an
* empty block as else block that jumps and move the
* unconditional jump to the if.
*/
if (sb instanceof IfThenElseBlock) {
IfThenElseBlock ifBlock = (IfThenElseBlock) sb;
if (ifBlock.elseBlock == null && ifBlock.jump != null) {
ifBlock.setElseBlock(new EmptyBlock());
ifBlock.elseBlock.moveJump(ifBlock.jump);
ifBlock.moveJump(jump);
/* consider this jump again */
jumps = jump;
continue;
}
}
/* if this is a jump at the end of a then block belonging
* to a if-then block without else part, and the if-then
* block is followed by a single block, then replace the
* if-then block with a if-then-else block and remove the
* unconditional jump.
* if-then block with a if-then-else block and move the
* unconditional jump to the if.
*/
if (sb instanceof IfThenElseBlock
&& sb.outer instanceof SequentialBlock
@ -333,6 +394,7 @@ public class FlowBlock {
if (ifBlock.elseBlock == null
&& (elseBlock.getNextFlowBlock() == succ
|| elseBlock.jump != null
|| elseBlock.jumpMayBeChanged())) {
ifBlock.replace(sequBlock);
@ -471,6 +533,51 @@ public class FlowBlock {
}
}
/**
* Fixes the addr chained list, after merging this block with succ.
*/
public void mergeAddr(FlowBlock succ) {
if (succ.nextByAddr == this || succ.prevByAddr == null) {
/* Merge succ with its nextByAddr.
* Note: succ.nextByAddr != null, since this is on the
* nextByAddr chain. */
succ.nextByAddr.addr = succ.addr;
succ.nextByAddr.length += succ.length;
succ.nextByAddr.prevByAddr = succ.prevByAddr;
if (succ.prevByAddr != null)
succ.prevByAddr.nextByAddr = succ.nextByAddr;
} else {
/* Merge succ with its prevByAddr */
succ.prevByAddr.length += succ.length;
succ.prevByAddr.nextByAddr = succ.nextByAddr;
if (succ.nextByAddr != null)
succ.nextByAddr.prevByAddr = succ.prevByAddr;
}
}
// /**
// * Mark all predecessors of this block as illegal, i.e. change the
// * successor to the ILLEGAL block.
// */
// public void markPredecessorsIllegal() {
// Enumeration preds = predecessors.elements();
// while (preds.hasMoreElements()) {
// FlowBlock pred = (FlowBlock) preds.nextElement();
// Jump jump = (Jump)pred.successors.remove(this);
// for (/**/; jump.next != null; jump = jump.next)
// jump.destination = ILLEGAL;
// jump.destination = ILLEGAL;
// jump.next = (Jump) pred.successors.get(jump.destination);
// if (jump.next == null)
// ILLEGAL.predecessors.addElement(this);
// pred.successors.put(jump.destination, jump);
// }
// predecessors.removeAllElements();
// }
/**
* Updates the in/out-Vectors of the structured block of the
* successing flow block simultanous to a T1 transformation.
@ -606,8 +713,14 @@ public class FlowBlock {
* a special precondition: The succ must be a simple instruction block,
* mustn't have another predecessor and all structured blocks in this
* flow block must be simple instruction blocks.
* @param succ The successing structured block that should be merged.
* @param length the length of the structured block.
*/
public void doSequentialT1(StructuredBlock succ, int length) {
if (Decompiler.isFlowDebugging) {
Decompiler.err.println("merging sequentialBlock: "+this);
Decompiler.err.println("and: "+succ);
}
VariableSet succIn = new VariableSet();
succ.fillInGenSet(succIn, this.gen);
@ -663,10 +776,8 @@ public class FlowBlock {
/* This will also set last modified to the new correct value. */
doTransformations();
/* Set addr+length to correct value. */
if (succ.addr < addr)
addr = succ.addr;
length += succ.length;
/* Set addr and length to correct value and update nextByAddr */
mergeAddr(succ);
/* T1 transformation succeeded */
checkConsistent();
@ -703,7 +814,7 @@ public class FlowBlock {
// }
// if (cb != null
// && cb.trueBlock.jump.destination.addr == addr + length) {
// && cb.trueBlock.jump.destination.addr == getNextAddr()) {
// loopBlock.moveJump(cb.trueBlock.jump);
// loopBlock.setCondition(cb.getInstruction().negate());
// loopBlock.setType(loopType);
@ -1028,8 +1139,8 @@ public class FlowBlock {
Decompiler.err.println("after T2: "+this);
if (Decompiler.debugAnalyze)
Decompiler.err.println("T2("+addr+","+(addr+length)
+") succeeded");
Decompiler.err.println("T2("+addr+","+getNextAddr()
+") succeeded");
/* T2 transformation succeeded. This may
* make another T1 analysis in the previous
* block possible.
@ -1048,11 +1159,10 @@ public class FlowBlock {
Decompiler.err.println
("No more successors applicable: "
+ start + " - " + end + "; "
+ addr + " - " + (addr+length));
+ addr + " - " + getNextAddr());
return changed;
} else {
if ((succ.addr == addr+length
|| succ.addr+succ.length == addr)
if ((nextByAddr == succ || succ.nextByAddr == this)
/* Only do T1 transformation if the blocks are
* adjacent. */
&& doT1(succ)) {
@ -1077,17 +1187,17 @@ public class FlowBlock {
Decompiler.err.println
("breaking analyze("
+ start + ", " + end + "); "
+ addr + " - " + (addr+length));
+ addr + " - " + getNextAddr());
return changed;
}
}
/* analyze succ, the new region is the
* continuous region of
* [start,end) \cap \compl [addr, addr+length)
* [start,end) \cap \compl [addr, getNextAddr())
* where succ.addr lies in.
*/
int newStart = (succ.addr > addr)
? addr+length : start;
? getNextAddr() : start;
int newEnd = (succ.addr > addr)
? end : addr;
if (succ.analyze(newStart, newEnd))
@ -1129,10 +1239,10 @@ public class FlowBlock {
* return early after a T2 trafo so call it
* until nothing more is possible.
*/
while (nextFlow.analyze(addr + length, end))
while (nextFlow.analyze(getNextAddr(), end))
changed = changed || true;
if (nextFlow.addr != addr + length)
if (nextFlow.addr != getNextAddr())
break;
/* Check if nextFlow has only the previous case
@ -1179,7 +1289,7 @@ public class FlowBlock {
*/
switchBlock.caseBlocks[i].subBlock.removeJump();
length += nextFlow.length;
mergeAddr(nextFlow);
lastFlow = nextFlow;
last = i;
@ -1211,13 +1321,22 @@ public class FlowBlock {
if (jump != null && jump.destination == null) {
if (jump.destAddr == -1)
jump.destination = END_OF_METHOD;
else
else if (jump.destAddr == instr.length)
// In this case, the jump must belong to dead code.
jump.destination = ILLEGAL;
else {
jump.destination = instr[jump.destAddr];
if (jump.destination == null)
throw new AssertError("Missing dest: "+jump.destAddr);
if (jump.destination == null)
throw new AssertError("Missing dest: "+jump.destAddr);
}
addSuccessor(jump);
}
}
if (getNextAddr() < instr.length) {
nextByAddr = instr[getNextAddr()];
nextByAddr.prevByAddr = this;
}
}
/**
@ -1261,6 +1380,45 @@ public class FlowBlock {
block.makeDeclaration(param);
}
/**
* Mark this block and all successing blocks as reachable.
*/
public void markReachable() {
if (reachable) {
// This block was already checked. This prevents infinite
// recursion.
return;
}
reachable = true;
Enumeration succs = successors.keys();
while (succs.hasMoreElements())
((FlowBlock) succs.nextElement()).markReachable();
}
/**
* Removes dead code, i.e. merges the dead flow block with there
* prevByAddr and removing their code completely. <br>
*
* Why is it necessary? Because jikes actually generates a lot
* of dead code in try, catch and finally blocks. This will break
* a lot of other code, e.g. checking that a catch handler has no
* entries or merging only adjacent blocks.
*
* @param flow The first flow block in this method.
*/
public static void removeDeadCode(FlowBlock flow) {
while (flow.nextByAddr != null) {
if (!flow.nextByAddr.reachable) {
Enumeration succs = flow.nextByAddr.successors.keys();
while (succs.hasMoreElements())
((FlowBlock) succs.nextElement()).predecessors
.removeElement(flow.nextByAddr);
flow.mergeAddr(flow.nextByAddr);
} else
flow = flow.nextByAddr;
}
}
/**
* Print the source code for this structured block. This handles
* everything that is unique for all structured blocks and calls
@ -1272,7 +1430,7 @@ public class FlowBlock {
{
if (predecessors.size() != 0) {
writer.untab();
writer.println(label+":");
writer.println(getLabel()+":");
writer.tab();
}
@ -1281,6 +1439,9 @@ public class FlowBlock {
}
block.dumpSource(writer);
if (nextByAddr != null)
nextByAddr.dumpSource(writer);
}
/**
@ -1313,10 +1474,10 @@ public class FlowBlock {
public String toString() {
try {
java.io.StringWriter strw = new java.io.StringWriter();
TabbedPrintWriter writer = new TabbedPrintWriter(strw, " ");
TabbedPrintWriter writer = new TabbedPrintWriter(strw);
writer.println(super.toString());
writer.tab();
dumpSource(writer);
block.dumpSource(writer);
return strw.toString();
} catch (java.io.IOException ex) {
return super.toString();

Write Preview
Loading…
Cancel
Save