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/*
* Copyright (C) 2008 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;
import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;
import java.util.HashMap;
import java.util.HashSet;
import java.util.Map;
import org.snapscript.dx.rop.code.LocalItem;
import org.snapscript.dx.rop.code.PlainCstInsn;
import org.snapscript.dx.rop.code.PlainInsn;
import org.snapscript.dx.rop.code.RegOps;
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.Rops;
import org.snapscript.dx.rop.code.SourcePosition;
import org.snapscript.dx.rop.code.ThrowingCstInsn;
import org.snapscript.dx.rop.cst.Constant;
import org.snapscript.dx.rop.cst.CstString;
import org.snapscript.dx.rop.cst.TypedConstant;
import org.snapscript.dx.rop.type.StdTypeList;
import org.snapscript.dx.rop.type.TypeBearer;
/**
* Collects constants that are used more than once at the top of the
* method block. This increases register usage by about 5% but decreases
* insn size by about 3%.
*/
public class ConstCollector {
/** Maximum constants to collect per method. Puts cap on reg use */
private static final int MAX_COLLECTED_CONSTANTS = 5;
/**
* Also collect string consts, although they can throw exceptions.
* This is off now because it just doesn't seem to gain a whole lot.
* TODO if you turn this on, you must change SsaInsn.hasSideEffect()
* to return false for const-string insns whose exceptions are not
* caught in the current method.
*/
private static boolean COLLECT_STRINGS = false;
/**
* If true, allow one local var to be involved with a collected const.
* Turned off because it mostly just inserts more moves.
*/
private static boolean COLLECT_ONE_LOCAL = false;
/** method we're processing */
private final SsaMethod ssaMeth;
/**
* Processes a method.
*
* @param ssaMethod {@code non-null;} method to process
*/
public static void process(SsaMethod ssaMethod) {
ConstCollector cc = new ConstCollector(ssaMethod);
cc.run();
}
/**
* Constructs an instance.
*
* @param ssaMethod {@code non-null;} method to process
*/
private ConstCollector(SsaMethod ssaMethod) {
this.ssaMeth = ssaMethod;
}
/**
* Applies the optimization.
*/
private void run() {
int regSz = ssaMeth.getRegCount();
ArrayList constantList
= getConstsSortedByCountUse();
int toCollect = Math.min(constantList.size(), MAX_COLLECTED_CONSTANTS);
SsaBasicBlock start = ssaMeth.getEntryBlock();
// Constant to new register containing the constant
HashMap newRegs
= new HashMap (toCollect);
for (int i = 0; i < toCollect; i++) {
TypedConstant cst = constantList.get(i);
RegisterSpec result
= RegisterSpec.make(ssaMeth.makeNewSsaReg(), cst);
Rop constRop = Rops.opConst(cst);
if (constRop.getBranchingness() == Rop.BRANCH_NONE) {
start.addInsnToHead(
new PlainCstInsn(Rops.opConst(cst),
SourcePosition.NO_INFO, result,
RegisterSpecList.EMPTY, cst));
} else {
// We need two new basic blocks along with the new insn
SsaBasicBlock entryBlock = ssaMeth.getEntryBlock();
SsaBasicBlock successorBlock
= entryBlock.getPrimarySuccessor();
// Insert a block containing the const insn.
SsaBasicBlock constBlock
= entryBlock.insertNewSuccessor(successorBlock);
constBlock.replaceLastInsn(
new ThrowingCstInsn(constRop, SourcePosition.NO_INFO,
RegisterSpecList.EMPTY,
StdTypeList.EMPTY, cst));
// Insert a block containing the move-result-pseudo insn.
SsaBasicBlock resultBlock
= constBlock.insertNewSuccessor(successorBlock);
PlainInsn insn
= new PlainInsn(
Rops.opMoveResultPseudo(result.getTypeBearer()),
SourcePosition.NO_INFO,
result, RegisterSpecList.EMPTY);
resultBlock.addInsnToHead(insn);
}
newRegs.put(cst, result);
}
updateConstUses(newRegs, regSz);
}
/**
* Gets all of the collectable constant values used in this method,
* sorted by most used first. Skips non-collectable consts, such as
* non-string object constants
*
* @return {@code non-null;} list of constants in most-to-least used order
*/
private ArrayList getConstsSortedByCountUse() {
int regSz = ssaMeth.getRegCount();
final HashMap countUses
= new HashMap();
/*
* Each collected constant can be used by just one local
* (used only if COLLECT_ONE_LOCAL is true).
*/
final HashSet usedByLocal
= new HashSet();
// Count how many times each const value is used.
for (int i = 0; i < regSz; i++) {
SsaInsn insn = ssaMeth.getDefinitionForRegister(i);
if (insn == null || insn.getOpcode() == null) continue;
RegisterSpec result = insn.getResult();
TypeBearer typeBearer = result.getTypeBearer();
if (!typeBearer.isConstant()) continue;
TypedConstant cst = (TypedConstant) typeBearer;
// Find defining instruction for move-result-pseudo instructions
if (insn.getOpcode().getOpcode() == RegOps.MOVE_RESULT_PSEUDO) {
int pred = insn.getBlock().getPredecessors().nextSetBit(0);
ArrayList predInsns;
predInsns = ssaMeth.getBlocks().get(pred).getInsns();
insn = predInsns.get(predInsns.size()-1);
}
if (insn.canThrow()) {
/*
* Don't move anything other than strings -- the risk
* of changing where an exception is thrown is too high.
*/
if (!(cst instanceof CstString) || !COLLECT_STRINGS) {
continue;
}
/*
* We can't move any throwable const whose throw will be
* caught, so don't count them.
*/
if (insn.getBlock().getSuccessors().cardinality() > 1) {
continue;
}
}
/*
* TODO: Might be nice to try and figure out which local
* wins most when collected.
*/
if (ssaMeth.isRegALocal(result)) {
if (!COLLECT_ONE_LOCAL) {
continue;
} else {
if (usedByLocal.contains(cst)) {
// Count one local usage only.
continue;
} else {
usedByLocal.add(cst);
}
}
}
Integer has = countUses.get(cst);
if (has == null) {
countUses.put(cst, 1);
} else {
countUses.put(cst, has + 1);
}
}
// Collect constants that have been reused.
ArrayList constantList = new ArrayList();
for (Map.Entry entry : countUses.entrySet()) {
if (entry.getValue() > 1) {
constantList.add(entry.getKey());
}
}
// Sort by use, with most used at the beginning of the list.
Collections.sort(constantList, new Comparator() {
public int compare(Constant a, Constant b) {
int ret;
ret = countUses.get(b) - countUses.get(a);
if (ret == 0) {
/*
* Provide sorting determinisim for constants with same
* usage count.
*/
ret = a.compareTo(b);
}
return ret;
}
@Override
public boolean equals (Object obj) {
return obj == this;
}
});
return constantList;
}
/**
* Inserts mark-locals if necessary when changing a register. If
* the definition of {@code origReg} is associated with a local
* variable, then insert a mark-local for {@code newReg} just below
* it. We expect the definition of {@code origReg} to ultimately
* be removed by the dead code eliminator
*
* @param origReg {@code non-null;} original register
* @param newReg {@code non-null;} new register that will replace
* {@code origReg}
*/
private void fixLocalAssignment(RegisterSpec origReg,
RegisterSpec newReg) {
for (SsaInsn use : ssaMeth.getUseListForRegister(origReg.getReg())) {
RegisterSpec localAssignment = use.getLocalAssignment();
if (localAssignment == null) {
continue;
}
if (use.getResult() == null) {
/*
* This is a mark-local. it will be updated when all uses
* are updated.
*/
continue;
}
LocalItem local = localAssignment.getLocalItem();
// Un-associate original use.
use.setResultLocal(null);
// Now add a mark-local to the new reg immediately after.
newReg = newReg.withLocalItem(local);
SsaInsn newInsn
= SsaInsn.makeFromRop(
new PlainInsn(Rops.opMarkLocal(newReg),
SourcePosition.NO_INFO, null,
RegisterSpecList.make(newReg)),
use.getBlock());
ArrayList insns = use.getBlock().getInsns();
insns.add(insns.indexOf(use) + 1, newInsn);
}
}
/**
* Updates all uses of various consts to use the values in the newly
* assigned registers.
*
* @param newRegs {@code non-null;} mapping between constant and new reg
* @param origRegCount {@code >=0;} original SSA reg count, not including
* newly added constant regs
*/
private void updateConstUses(HashMap newRegs,
int origRegCount) {
/*
* set of constants associated with a local variable; used
* only if COLLECT_ONE_LOCAL is true.
*/
final HashSet usedByLocal
= new HashSet();
final ArrayList[] useList = ssaMeth.getUseListCopy();
for (int i = 0; i < origRegCount; i++) {
SsaInsn insn = ssaMeth.getDefinitionForRegister(i);
if (insn == null) {
continue;
}
final RegisterSpec origReg = insn.getResult();
TypeBearer typeBearer = insn.getResult().getTypeBearer();
if (!typeBearer.isConstant()) continue;
TypedConstant cst = (TypedConstant) typeBearer;
final RegisterSpec newReg = newRegs.get(cst);
if (newReg == null) {
continue;
}
if (ssaMeth.isRegALocal(origReg)) {
if (!COLLECT_ONE_LOCAL) {
continue;
} else {
/*
* TODO: If the same local gets the same cst
* multiple times, it would be nice to reuse the
* register.
*/
if (usedByLocal.contains(cst)) {
continue;
} else {
usedByLocal.add(cst);
fixLocalAssignment(origReg, newRegs.get(cst));
}
}
}
// maps an original const register to the new collected register
RegisterMapper mapper = new RegisterMapper() {
@Override
public int getNewRegisterCount() {
return ssaMeth.getRegCount();
}
@Override
public RegisterSpec map(RegisterSpec registerSpec) {
if (registerSpec.getReg() == origReg.getReg()) {
return newReg.withLocalItem(
registerSpec.getLocalItem());
}
return registerSpec;
}
};
for (SsaInsn use : useList[origReg.getReg()]) {
if (use.canThrow()
&& use.getBlock().getSuccessors().cardinality() > 1) {
continue;
}
use.mapSourceRegisters(mapper);
}
}
}
}
