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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 org.snapscript.dx.ssa.back;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.BitSet;
import java.util.Comparator;
import org.snapscript.dx.rop.code.BasicBlock;
import org.snapscript.dx.rop.code.BasicBlockList;
import org.snapscript.dx.rop.code.InsnList;
import org.snapscript.dx.rop.code.RegisterSpec;
import org.snapscript.dx.rop.code.RegisterSpecList;
import org.snapscript.dx.rop.code.Rop;
import org.snapscript.dx.rop.code.RopMethod;
import org.snapscript.dx.rop.code.Rops;
import org.snapscript.dx.ssa.BasicRegisterMapper;
import org.snapscript.dx.ssa.PhiInsn;
import org.snapscript.dx.ssa.RegisterMapper;
import org.snapscript.dx.ssa.SsaBasicBlock;
import org.snapscript.dx.ssa.SsaInsn;
import org.snapscript.dx.ssa.SsaMethod;
import org.snapscript.dx.util.Hex;
import org.snapscript.dx.util.IntList;
/**
* Converts a method in SSA form to ROP form.
*/
public class SsaToRop {
/** local debug flag */
private static final boolean DEBUG = false;
/** {@code non-null;} method to process */
private final SsaMethod ssaMeth;
/**
* {@code true} if the converter should attempt to minimize
* the rop-form register count
*/
private final boolean minimizeRegisters;
/** {@code non-null;} interference graph */
private final InterferenceGraph interference;
/**
* Converts a method in SSA form to ROP form.
*
* @param ssaMeth {@code non-null;} method to process
* @param minimizeRegisters {@code true} if the converter should
* attempt to minimize the rop-form register count
* @return {@code non-null;} rop-form output
*/
public static RopMethod convertToRopMethod(SsaMethod ssaMeth,
boolean minimizeRegisters) {
return new SsaToRop(ssaMeth, minimizeRegisters).convert();
}
/**
* Constructs an instance.
*
* @param ssaMeth {@code non-null;} method to process
* @param minimizeRegisters {@code true} if the converter should
* attempt to minimize the rop-form register count
*/
private SsaToRop(SsaMethod ssaMethod, boolean minimizeRegisters) {
this.minimizeRegisters = minimizeRegisters;
this.ssaMeth = ssaMethod;
this.interference =
LivenessAnalyzer.constructInterferenceGraph(ssaMethod);
}
/**
* Performs the conversion.
*
* @return {@code non-null;} rop-form output
*/
private RopMethod convert() {
if (DEBUG) {
interference.dumpToStdout();
}
// These are other allocators for debugging or historical comparison:
// allocator = new NullRegisterAllocator(ssaMeth, interference);
// allocator = new FirstFitAllocator(ssaMeth, interference);
RegisterAllocator allocator =
new FirstFitLocalCombiningAllocator(ssaMeth, interference,
minimizeRegisters);
RegisterMapper mapper = allocator.allocateRegisters();
if (DEBUG) {
System.out.println("Printing reg map");
System.out.println(((BasicRegisterMapper)mapper).toHuman());
}
ssaMeth.setBackMode();
ssaMeth.mapRegisters(mapper);
removePhiFunctions();
if (allocator.wantsParamsMovedHigh()) {
moveParametersToHighRegisters();
}
removeEmptyGotos();
RopMethod ropMethod = new RopMethod(convertBasicBlocks(),
ssaMeth.blockIndexToRopLabel(ssaMeth.getEntryBlockIndex()));
ropMethod = new IdenticalBlockCombiner(ropMethod).process();
return ropMethod;
}
/**
* Removes all blocks containing only GOTOs from the control flow.
* Although much of this work will be done later when converting
* from rop to dex, not all simplification cases can be handled
* there. Furthermore, any no-op block between the exit block and
* blocks containing the real return or throw statements must be
* removed.
*/
private void removeEmptyGotos() {
final ArrayList blocks = ssaMeth.getBlocks();
ssaMeth.forEachBlockDepthFirst(false, new SsaBasicBlock.Visitor() {
public void visitBlock(SsaBasicBlock b, SsaBasicBlock parent) {
ArrayList insns = b.getInsns();
if ((insns.size() == 1)
&& (insns.get(0).getOpcode() == Rops.GOTO)) {
BitSet preds = (BitSet) b.getPredecessors().clone();
for (int i = preds.nextSetBit(0); i >= 0;
i = preds.nextSetBit(i + 1)) {
SsaBasicBlock pb = blocks.get(i);
pb.replaceSuccessor(b.getIndex(),
b.getPrimarySuccessorIndex());
}
}
}
});
}
/**
* See Appel 19.6. To remove the phi instructions in an edge-split
* SSA representation we know we can always insert a move in a
* predecessor block.
*/
private void removePhiFunctions() {
ArrayList blocks = ssaMeth.getBlocks();
for (SsaBasicBlock block : blocks) {
// Add moves in all the pred blocks for each phi insn.
block.forEachPhiInsn(new PhiVisitor(blocks));
// Delete the phi insns.
block.removeAllPhiInsns();
}
/*
* After all move insns have been added, sort them so they don't
* destructively interfere.
*/
for (SsaBasicBlock block : blocks) {
block.scheduleMovesFromPhis();
}
}
/**
* Helper for {@link #removePhiFunctions}: PhiSuccessorUpdater for
* adding move instructions to predecessors based on phi insns.
*/
private static class PhiVisitor implements PhiInsn.Visitor {
private final ArrayList blocks;
public PhiVisitor(ArrayList blocks) {
this.blocks = blocks;
}
public void visitPhiInsn(PhiInsn insn) {
RegisterSpecList sources = insn.getSources();
RegisterSpec result = insn.getResult();
int sz = sources.size();
for (int i = 0; i < sz; i++) {
RegisterSpec source = sources.get(i);
SsaBasicBlock predBlock = blocks.get(
insn.predBlockIndexForSourcesIndex(i));
predBlock.addMoveToEnd(result, source);
}
}
}
/**
* Moves the parameter registers, which allocateRegisters() places
* at the bottom of the frame, up to the top of the frame to match
* Dalvik calling convention.
*/
private void moveParametersToHighRegisters() {
int paramWidth = ssaMeth.getParamWidth();
BasicRegisterMapper mapper
= new BasicRegisterMapper(ssaMeth.getRegCount());
int regCount = ssaMeth.getRegCount();
for (int i = 0; i < regCount; i++) {
if (i < paramWidth) {
mapper.addMapping(i, regCount - paramWidth + i, 1);
} else {
mapper.addMapping(i, i - paramWidth, 1);
}
}
if (DEBUG) {
System.out.printf("Moving %d registers from 0 to %d\n",
paramWidth, regCount - paramWidth);
}
ssaMeth.mapRegisters(mapper);
}
/**
* @return rop-form basic block list
*/
private BasicBlockList convertBasicBlocks() {
ArrayList blocks = ssaMeth.getBlocks();
// Exit block may be null.
SsaBasicBlock exitBlock = ssaMeth.getExitBlock();
ssaMeth.computeReachability();
int ropBlockCount = ssaMeth.getCountReachableBlocks();
// Don't count the exit block, if it exists and is reachable.
ropBlockCount -= (exitBlock != null && exitBlock.isReachable()) ? 1 : 0;
BasicBlockList result = new BasicBlockList(ropBlockCount);
// Convert all the reachable blocks except the exit block.
int ropBlockIndex = 0;
for (SsaBasicBlock b : blocks) {
if (b.isReachable() && b != exitBlock) {
result.set(ropBlockIndex++, convertBasicBlock(b));
}
}
// The exit block, which is discarded, must do nothing.
if (exitBlock != null && exitBlock.getInsns().size() != 0) {
throw new RuntimeException(
"Exit block must have no insns when leaving SSA form");
}
return result;
}
/**
* Validates that a basic block is a valid end predecessor. It must
* end in a RETURN or a THROW. Throws a runtime exception on error.
*
* @param b {@code non-null;} block to validate
* @throws RuntimeException on error
*/
private void verifyValidExitPredecessor(SsaBasicBlock b) {
ArrayList insns = b.getInsns();
SsaInsn lastInsn = insns.get(insns.size() - 1);
Rop opcode = lastInsn.getOpcode();
if (opcode.getBranchingness() != Rop.BRANCH_RETURN
&& opcode != Rops.THROW) {
throw new RuntimeException("Exit predecessor must end"
+ " in valid exit statement.");
}
}
/**
* Converts a single basic block to rop form.
*
* @param block SSA block to process
* @return {@code non-null;} ROP block
*/
private BasicBlock convertBasicBlock(SsaBasicBlock block) {
IntList successorList = block.getRopLabelSuccessorList();
int primarySuccessorLabel = block.getPrimarySuccessorRopLabel();
// Filter out any reference to the SSA form's exit block.
// Exit block may be null.
SsaBasicBlock exitBlock = ssaMeth.getExitBlock();
int exitRopLabel = (exitBlock == null) ? -1 : exitBlock.getRopLabel();
if (successorList.contains(exitRopLabel)) {
if (successorList.size() > 1) {
throw new RuntimeException(
"Exit predecessor must have no other successors"
+ Hex.u2(block.getRopLabel()));
} else {
successorList = IntList.EMPTY;
primarySuccessorLabel = -1;
verifyValidExitPredecessor(block);
}
}
successorList.setImmutable();
BasicBlock result = new BasicBlock(
block.getRopLabel(), convertInsns(block.getInsns()),
successorList,
primarySuccessorLabel);
return result;
}
/**
* Converts an insn list to rop form.
*
* @param ssaInsns {@code non-null;} old instructions
* @return {@code non-null;} immutable instruction list
*/
private InsnList convertInsns(ArrayList ssaInsns) {
int insnCount = ssaInsns.size();
InsnList result = new InsnList(insnCount);
for (int i = 0; i < insnCount; i++) {
result.set(i, ssaInsns.get(i).toRopInsn());
}
result.setImmutable();
return result;
}
/**
* Note: This method is not presently used.
*
* @return a list of registers ordered by most-frequently-used to
* least-frequently-used. Each register is listed once and only
* once.
*/
public int[] getRegistersByFrequency() {
int regCount = ssaMeth.getRegCount();
Integer[] ret = new Integer[regCount];
for (int i = 0; i < regCount; i++) {
ret[i] = i;
}
Arrays.sort(ret, new Comparator() {
public int compare(Integer o1, Integer o2) {
return ssaMeth.getUseListForRegister(o2).size()
- ssaMeth.getUseListForRegister(o1).size();
}
});
int result[] = new int[regCount];
for (int i = 0; i < regCount; i++) {
result[i] = ret[i];
}
return result;
}
}
