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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 com.android.dx.cf.code;
import com.android.dex.util.ExceptionWithContext;
import com.android.dx.rop.cst.CstType;
import com.android.dx.rop.type.StdTypeList;
import com.android.dx.rop.type.Type;
import com.android.dx.util.IntList;
/**
* Representation of a Java method execution frame. A frame consists
* of a set of locals and a value stack, and it can be told to act on
* them to load and store values between them and an "arguments /
* results" area.
*/
public final class Frame {
/** {@code non-null;} the locals */
private final LocalsArray locals;
/** {@code non-null;} the stack */
private final ExecutionStack stack;
/** {@code null-ok;} stack of labels of subroutines that this block is nested in */
private final IntList subroutines;
/**
* Constructs an instance.
*
* @param locals {@code non-null;} the locals array to use
* @param stack {@code non-null;} the execution stack to use
*/
private Frame(LocalsArray locals, ExecutionStack stack) {
this(locals, stack, IntList.EMPTY);
}
/**
* Constructs an instance.
*
* @param locals {@code non-null;} the locals array to use
* @param stack {@code non-null;} the execution stack to use
* @param subroutines {@code non-null;} list of subroutine start labels for
* subroutines this frame is nested in
*/
private Frame(LocalsArray locals,
ExecutionStack stack, IntList subroutines) {
if (locals == null) {
throw new NullPointerException("locals == null");
}
if (stack == null) {
throw new NullPointerException("stack == null");
}
subroutines.throwIfMutable();
this.locals = locals;
this.stack = stack;
this.subroutines = subroutines;
}
/**
* Constructs an instance. The locals array initially consists of
* all-uninitialized values (represented as {@code null}s) and
* the stack starts out empty.
*
* @param maxLocals {@code >= 0;} the maximum number of locals this instance
* can refer to
* @param maxStack {@code >= 0;} the maximum size of the stack for this
* instance
*/
public Frame(int maxLocals, int maxStack) {
this(new OneLocalsArray(maxLocals), new ExecutionStack(maxStack));
}
/**
* Makes and returns a mutable copy of this instance. The copy
* contains copies of the locals and stack (that is, it doesn't
* share them with the original).
*
* @return {@code non-null;} the copy
*/
public Frame copy() {
return new Frame(locals.copy(), stack.copy(), subroutines);
}
/**
* Makes this instance immutable.
*/
public void setImmutable() {
locals.setImmutable();
stack.setImmutable();
// "subroutines" is always immutable
}
/**
* Replaces all the occurrences of the given uninitialized type in
* this frame with its initialized equivalent.
*
* @param type {@code non-null;} type to replace
*/
public void makeInitialized(Type type) {
locals.makeInitialized(type);
stack.makeInitialized(type);
}
/**
* Gets the locals array for this instance.
*
* @return {@code non-null;} the locals array
*/
public LocalsArray getLocals() {
return locals;
}
/**
* Gets the execution stack for this instance.
*
* @return {@code non-null;} the execution stack
*/
public ExecutionStack getStack() {
return stack;
}
/**
* Returns the largest subroutine nesting this block may be in. An
* empty list is returned if this block is not in any subroutine.
* Subroutines are identified by the label of their start block. The
* list is ordered such that the deepest nesting (the actual subroutine
* this block is in) is the last label in the list.
*
* @return {@code non-null;} list as noted above
*/
public IntList getSubroutines() {
return subroutines;
}
/**
* Initialize this frame with the method's parameters. Used for the first
* frame.
*
* @param params Type list of method parameters.
*/
public void initializeWithParameters(StdTypeList params) {
int at = 0;
int sz = params.size();
for (int i = 0; i < sz; i++) {
Type one = params.get(i);
locals.set(at, one);
at += one.getCategory();
}
}
/**
* Returns a Frame instance representing the frame state that should
* be used when returning from a subroutine. The stack state of all
* subroutine invocations is identical, but the locals state may differ.
*
* @param startLabel {@code >=0;} The label of the returning subroutine's
* start block
* @param subLabel {@code >=0;} A calling label of a subroutine
* @return {@code null-ok;} an appropriatly-constructed instance, or null
* if label is not in the set
*/
public Frame subFrameForLabel(int startLabel, int subLabel) {
LocalsArray subLocals = null;
if (locals instanceof LocalsArraySet) {
subLocals = ((LocalsArraySet)locals).subArrayForLabel(subLabel);
}
IntList newSubroutines;
try {
newSubroutines = subroutines.mutableCopy();
if (newSubroutines.pop() != startLabel) {
throw new RuntimeException("returning from invalid subroutine");
}
newSubroutines.setImmutable();
} catch (IndexOutOfBoundsException ex) {
throw new RuntimeException("returning from invalid subroutine");
} catch (NullPointerException ex) {
throw new NullPointerException("can't return from non-subroutine");
}
return (subLocals == null) ? null
: new Frame(subLocals, stack, newSubroutines);
}
/**
* Merges two frames. If the merged result is the same as this frame,
* then this instance is returned.
*
* @param other {@code non-null;} another frame
* @return {@code non-null;} the result of merging the two frames
*/
public Frame mergeWith(Frame other) {
LocalsArray resultLocals;
ExecutionStack resultStack;
IntList resultSubroutines;
resultLocals = getLocals().merge(other.getLocals());
resultStack = getStack().merge(other.getStack());
resultSubroutines = mergeSubroutineLists(other.subroutines);
resultLocals = adjustLocalsForSubroutines(
resultLocals, resultSubroutines);
if ((resultLocals == getLocals())
&& (resultStack == getStack())
&& subroutines == resultSubroutines) {
return this;
}
return new Frame(resultLocals, resultStack, resultSubroutines);
}
/**
* Merges this frame's subroutine lists with another. The result
* is the deepest common nesting (effectively, the common prefix of the
* two lists).
*
* @param otherSubroutines label list of subroutine start blocks, from
* least-nested to most-nested.
* @return {@code non-null;} merged subroutine nest list as described above
*/
private IntList mergeSubroutineLists(IntList otherSubroutines) {
if (subroutines.equals(otherSubroutines)) {
return subroutines;
}
IntList resultSubroutines = new IntList();
int szSubroutines = subroutines.size();
int szOthers = otherSubroutines.size();
for (int i = 0; i < szSubroutines && i < szOthers
&& (subroutines.get(i) == otherSubroutines.get(i)); i++) {
resultSubroutines.add(i);
}
resultSubroutines.setImmutable();
return resultSubroutines;
}
/**
* Adjusts a locals array to account for a merged subroutines list.
* If a frame merge results in, effectively, a subroutine return through
* a throw then the current locals will be a LocalsArraySet that will
* need to be trimmed of all OneLocalsArray elements that relevent to
* the subroutine that is returning.
*
* @param locals {@code non-null;} LocalsArray from before a merge
* @param subroutines {@code non-null;} a label list of subroutine start blocks
* representing the subroutine nesting of the block being merged into.
* @return {@code non-null;} locals set appropriate for merge
*/
private static LocalsArray adjustLocalsForSubroutines(
LocalsArray locals, IntList subroutines) {
if (! (locals instanceof LocalsArraySet)) {
// nothing to see here
return locals;
}
LocalsArraySet laSet = (LocalsArraySet)locals;
if (subroutines.size() == 0) {
/*
* We've merged from a subroutine context to a non-subroutine
* context, likely via a throw. Our successor will only need
* to consider the primary locals state, not the state of
* all possible subroutine paths.
*/
return laSet.getPrimary();
}
/*
* It's unclear to me if the locals set needs to be trimmed here.
* If it does, then I believe it is all of the calling blocks
* in the subroutine at the end of "subroutines" passed into
* this method that should be removed.
*/
return laSet;
}
/**
* Merges this frame with the frame of a subroutine caller at
* {@code predLabel}. Only called on the frame at the first
* block of a subroutine.
*
* @param other {@code non-null;} another frame
* @param subLabel label of subroutine start block
* @param predLabel label of calling block
* @return {@code non-null;} the result of merging the two frames
*/
public Frame mergeWithSubroutineCaller(Frame other, int subLabel,
int predLabel) {
LocalsArray resultLocals;
ExecutionStack resultStack;
resultLocals = getLocals().mergeWithSubroutineCaller(
other.getLocals(), predLabel);
resultStack = getStack().merge(other.getStack());
IntList newOtherSubroutines = other.subroutines.mutableCopy();
newOtherSubroutines.add(subLabel);
newOtherSubroutines.setImmutable();
if ((resultLocals == getLocals())
&& (resultStack == getStack())
&& subroutines.equals(newOtherSubroutines)) {
return this;
}
IntList resultSubroutines;
if (subroutines.equals(newOtherSubroutines)) {
resultSubroutines = subroutines;
} else {
/*
* The new subroutines list should be the deepest of the two
* lists being merged, but the postfix of the resultant list
* must be equal to the shorter list.
*/
IntList nonResultSubroutines;
if (subroutines.size() > newOtherSubroutines.size()) {
resultSubroutines = subroutines;
nonResultSubroutines = newOtherSubroutines;
} else {
resultSubroutines = newOtherSubroutines;
nonResultSubroutines = subroutines;
}
int szResult = resultSubroutines.size();
int szNonResult = nonResultSubroutines.size();
for (int i = szNonResult - 1; i >=0; i-- ) {
if (nonResultSubroutines.get(i)
!= resultSubroutines.get(
i + (szResult - szNonResult))) {
throw new
RuntimeException("Incompatible merged subroutines");
}
}
}
return new Frame(resultLocals, resultStack, resultSubroutines);
}
/**
* Makes a frame for a subroutine start block, given that this is the
* ending frame of one of the subroutine's calling blocks. Subroutine
* calls may be nested and thus may have nested locals state, so we
* start with an initial state as seen by the subroutine, but keep track
* of the individual locals states that will be expected when the individual
* subroutine calls return.
*
* @param subLabel label of subroutine start block
* @param callerLabel {@code >=0;} label of the caller block where this frame
* came from.
* @return a new instance to begin a called subroutine.
*/
public Frame makeNewSubroutineStartFrame(int subLabel, int callerLabel) {
IntList newSubroutines = subroutines.mutableCopy();
newSubroutines.add(subLabel);
Frame newFrame = new Frame(locals.getPrimary(), stack,
IntList.makeImmutable(subLabel));
return newFrame.mergeWithSubroutineCaller(this, subLabel, callerLabel);
}
/**
* Makes a new frame for an exception handler block invoked from this
* frame.
*
* @param exceptionClass exception that the handler block will handle
* @return new frame
*/
public Frame makeExceptionHandlerStartFrame(CstType exceptionClass) {
ExecutionStack newStack = getStack().copy();
newStack.clear();
newStack.push(exceptionClass);
return new Frame(getLocals(), newStack, subroutines);
}
/**
* Annotates (adds context to) the given exception with information
* about this frame.
*
* @param ex {@code non-null;} the exception to annotate
*/
public void annotate(ExceptionWithContext ex) {
locals.annotate(ex);
stack.annotate(ex);
}
}
