src/main/java/com/android/tools/r8/ir/code/Phi.java - r8 - Git at Google

 // Copyright (c) 2016, the R8 project authors. Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 package com.android.tools.r8.ir.code;

 import com.android.tools.r8.errors.CompilationError;
 import com.android.tools.r8.graph.DebugLocalInfo;
 import com.android.tools.r8.ir.code.BasicBlock.EdgeType;
 import com.android.tools.r8.ir.conversion.IRBuilder;
 import com.android.tools.r8.utils.CfgPrinter;
 import com.android.tools.r8.utils.ListUtils;
 import com.android.tools.r8.utils.StringUtils;
 import java.util.ArrayList;
 import java.util.HashSet;
 import java.util.List;
 import java.util.Map;
 import java.util.Set;

 public class Phi extends Value {

   private final BasicBlock block;
   private final List<Value> operands = new ArrayList<>();

   // Trivial phis are eliminated during IR construction. When a trivial phi is eliminated
   // we need to update all references to it. A phi can be referenced from phis, instructions
   // and current definition mappings. This list contains the current definitions mappings that
   // contain this phi.
   private List<Map<Integer, Value>> definitionUsers = new ArrayList<>();

   // The computed out type is not always the same as 'this.type' because of the type
   // confusion around null and constant zero. The null object can be used in a single
   // context (if tests) and the single 0 can be used as null. A phi can therefore
   // have either of the creation types 'single' and 'object' depending on the use that
   // triggered the creation of the phi. We therefore have to delay the output type
   // computation of the phi until all operands are known.
   private MoveType outType = null;

   public Phi(int number, BasicBlock block, MoveType type, DebugLocalInfo local) {
     super(number, type, local == null ? null : new DebugInfo(local, null));
     this.block = block;
     block.addPhi(this);
   }

   @Override
   public boolean isPhi() {
     return true;
   }

   @Override
   public Phi asPhi() {
     return this;
   }

   public BasicBlock getBlock() {
     return block;
   }

   public void addOperands(IRBuilder builder, int register) {
     // Phi operands are only filled in once to complete the phi. Some phis are incomplete for a
     // period of time to break cycles. When the cycle has been resolved they are completed
     // exactly once by adding the operands.
     assert operands.isEmpty();
     boolean canBeNull = false;
     if (block.getPredecessors().size() == 0) {
       throwUndefinedValueError();
     }
     for (BasicBlock pred : block.getPredecessors()) {
       EdgeType edgeType = pred.getEdgeType(block);
       // Since this read has been delayed we must provide the local info for the value.
       Value operand = builder.readRegister(register, pred, edgeType, type, getLocalInfo());
       canBeNull |= operand.canBeNull();
       appendOperand(operand);
     }
     if (!canBeNull) {
       markNeverNull();
     }
     removeTrivialPhi();
   }

   public void addOperands(List<Value> operands) {
     // Phi operands are only filled in once to complete the phi. Some phis are incomplete for a
     // period of time to break cycles. When the cycle has been resolved they are completed
     // exactly once by adding the operands.
     assert this.operands.isEmpty();
     boolean canBeNull = false;
     if (operands.size() == 0) {
       throwUndefinedValueError();
     }
     for (Value operand : operands) {
       canBeNull |= operand.canBeNull();
       appendOperand(operand);
     }
     if (!canBeNull) {
       markNeverNull();
     }
     removeTrivialPhi();
   }

   private void throwUndefinedValueError() {
     throw new CompilationError(
         "Undefined value encountered during compilation. "
             + "This is typically caused by invalid dex input that uses a register "
             + "that is not define on all control-flow paths leading to the use.");
   }

   private void appendOperand(Value operand) {
     operands.add(operand);
     operand.addPhiUser(this);
   }

   public Value getOperand(int predIndex) {
     return operands.get(predIndex);
   }

   public List<Value> getOperands() {
     return operands;
   }

   public void removeOperand(int index) {
     operands.get(index).removePhiUser(this);
     operands.remove(index);
   }

   public void removeOperandsByIndex(List<Integer> operandsToRemove) {
     if (operandsToRemove.isEmpty()) {
       return;
     }
     List<Value> copy = new ArrayList<>(operands);
     operands.clear();
     int current = 0;
     for (int i : operandsToRemove) {
       operands.addAll(copy.subList(current, i));
       copy.get(i).removePhiUser(this);
       current = i + 1;
     }
     operands.addAll(copy.subList(current, copy.size()));
   }

   public void replace(int predIndex, Value newValue) {
     Value current = operands.get(predIndex);
     operands.set(predIndex, newValue);
     newValue.addPhiUser(this);
     current.removePhiUser(this);
   }

   // Removing the phi user from the current value leads to concurrent modification errors
   // during trivial phi elimination. It is safe to not remove the phi user from current
   // since current will be unreachable after trivial phi elimination.
   // TODO(ager): can we unify the these replace methods and avoid the concurrent modification
   // issue?
   private void replaceTrivialPhi(Value current, Value newValue) {
     for (int i = 0; i < operands.size(); i++) {
       if (operands.get(i) == current) {
         operands.set(i, newValue);
         newValue.addPhiUser(this);
       }
     }
   }

   public boolean isTrivialPhi() {
     Value same = null;
     for (Value op : operands) {
       if (op == same || op == this) {
         // Have only seen one value other than this.
         continue;
       }
       if (same != null) {
         // Merged at least two values and is therefore not trivial.
         return false;
       }
       same = op;
     }
     return true;
   }

   public void removeTrivialPhi() {
     Value same = null;
     for (Value op : operands) {
       if (op == same || op == this) {
         // Have only seen one value other than this.
         continue;
       }
       if (same != null) {
         // Merged at least two values and is therefore not trivial.
         assert !isTrivialPhi();
         return;
       }
       same = op;
     }
     assert isTrivialPhi();
     // Removing this phi, so get rid of it as a phi user from all of the operands to avoid
     // recursively getting back here with the same phi. If the phi has itself as an operand
     // that also removes the self-reference.
     for (Value op : operands) {
       op.removePhiUser(this);
     }
     // Replace this phi with the unique value in all users.
     for (Instruction user : uniqueUsers()) {
       user.replaceValue(this, same);
     }
     for (Phi user : uniquePhiUsers()) {
       user.replaceTrivialPhi(this, same);
     }
     if (debugUsers() != null) {
       for (Instruction user : debugUsers()) {
         user.replaceDebugPhi(this, same);
       }
     }
     // If IR construction is taking place, update the definition users.
     if (definitionUsers != null) {
       for (Map<Integer, Value> user : definitionUsers) {
         for (Map.Entry<Integer, Value> entry : user.entrySet()) {
           if (entry.getValue() == this) {
             entry.setValue(same);
             if (same.isPhi()) {
               same.asPhi().addDefinitionsUser(user);
             }
           }
         }
       }
     }
     // Try to simplify phi users that might now have become trivial.
     for (Phi user : uniquePhiUsers()) {
       user.removeTrivialPhi();
     }
     // Get rid of the phi itself.
     block.removePhi(this);
   }

   public String printPhi() {
     StringBuilder builder = new StringBuilder();
     builder.append("v");
     builder.append(number);
     if (getLocalInfo() != null) {
       builder.append("(").append(getLocalInfo()).append(")");
     }
     builder.append(" <- phi");
     StringUtils.append(builder, ListUtils.map(operands, Value::toString));
     return builder.toString();
   }

   public void print(CfgPrinter printer) {
     int uses = numberOfPhiUsers() + numberOfUsers();
     printer
         .print("0 ")                 // bci
         .append(uses)                // use
         .append(" v").append(number) // tid
         .append(" Phi");
     for (Value operand : operands) {
       printer.append(" v").append(operand.number);
     }
   }

   public void addDefinitionsUser(Map<Integer, Value> currentDefinitions) {
     definitionUsers.add(currentDefinitions);
   }

   public void removeDefinitionsUser(Map<Integer, Value> currentDefinitions) {
     definitionUsers.remove(currentDefinitions);
   }

   public void clearDefinitionsUsers() {
     definitionUsers = null;
   }

   private boolean isSingleConstZero(Value value) {
     return value.definition != null && value.definition.isConstNumber() &&
         value.definition.asConstNumber().isZero() &&
         value.outType() == MoveType.SINGLE;
   }

   private MoveType computeOutType(Set<Phi> active) {
     if (outType != null) {
       return outType;
     }
     active.add(this);
     // Go through non-phi operands first to determine if we have an operand that dictates the type.
     for (Value operand : operands) {
       // Since a constant zero can be either an integer or an Object (null) we skip them
       // when computing types and rely on other operands to specify the actual type.
       if (!operand.isPhi() && !isSingleConstZero(operand)) {
         return operand.outType();
       }
     }
     // We did not find a non-phi operand that dictates the type. Recurse on phi arguments.
     for (Value operand : operands) {
       if (operand.isPhi() && !active.contains(operand)) {
         MoveType phiType = operand.asPhi().computeOutType(active);
         // TODO(zerny): If we had a CONST_ZERO type element, we could often avoid going through
         // all phis. We would only have to recurse until we got a non CONST_ZERO out type.
         if (phiType != MoveType.SINGLE) {
           return phiType;
         }
       }
     }
     // All operands were the constant zero or phis with out type SINGLE and the out type is either
     // object or single depending on the use. Since all inputs have out type SINGLE it is safe to
     // return MoveType.SINGLE here.
     assert type == MoveType.SINGLE || type == MoveType.OBJECT;
     return MoveType.SINGLE;
   }

   @Override
   public MoveType outType() {
     if (outType != null) {
       return outType;
     }
     return computeOutType(new HashSet<>());
   }

   @Override
   public boolean isConstant() {
     return false;
   }

   public boolean needsRegister() {
     return true;
   }
 }
	// Copyright (c) 2016, the R8 project authors. Please see the AUTHORS file
	// for details. All rights reserved. Use of this source code is governed by a
	// BSD-style license that can be found in the LICENSE file.
	package com.android.tools.r8.ir.code;

	import com.android.tools.r8.errors.CompilationError;
	import com.android.tools.r8.graph.DebugLocalInfo;
	import com.android.tools.r8.ir.code.BasicBlock.EdgeType;
	import com.android.tools.r8.ir.conversion.IRBuilder;
	import com.android.tools.r8.utils.CfgPrinter;
	import com.android.tools.r8.utils.ListUtils;
	import com.android.tools.r8.utils.StringUtils;
	import java.util.ArrayList;
	import java.util.HashSet;
	import java.util.List;
	import java.util.Map;
	import java.util.Set;

	public class Phi extends Value {

	private final BasicBlock block;
	private final List<Value> operands = new ArrayList<>();

	// Trivial phis are eliminated during IR construction. When a trivial phi is eliminated
	// we need to update all references to it. A phi can be referenced from phis, instructions
	// and current definition mappings. This list contains the current definitions mappings that
	// contain this phi.
	private List<Map<Integer, Value>> definitionUsers = new ArrayList<>();

	// The computed out type is not always the same as 'this.type' because of the type
	// confusion around null and constant zero. The null object can be used in a single
	// context (if tests) and the single 0 can be used as null. A phi can therefore
	// have either of the creation types 'single' and 'object' depending on the use that
	// triggered the creation of the phi. We therefore have to delay the output type
	// computation of the phi until all operands are known.
	private MoveType outType = null;

	public Phi(int number, BasicBlock block, MoveType type, DebugLocalInfo local) {
	super(number, type, local == null ? null : new DebugInfo(local, null));
	this.block = block;
	block.addPhi(this);
	}

	@Override
	public boolean isPhi() {
	return true;
	}

	@Override
	public Phi asPhi() {
	return this;
	}

	public BasicBlock getBlock() {
	return block;
	}

	public void addOperands(IRBuilder builder, int register) {
	// Phi operands are only filled in once to complete the phi. Some phis are incomplete for a
	// period of time to break cycles. When the cycle has been resolved they are completed
	// exactly once by adding the operands.
	assert operands.isEmpty();
	boolean canBeNull = false;
	if (block.getPredecessors().size() == 0) {
	throwUndefinedValueError();
	}
	for (BasicBlock pred : block.getPredecessors()) {
	EdgeType edgeType = pred.getEdgeType(block);
	// Since this read has been delayed we must provide the local info for the value.
	Value operand = builder.readRegister(register, pred, edgeType, type, getLocalInfo());
	canBeNull \|= operand.canBeNull();
	appendOperand(operand);
	}
	if (!canBeNull) {
	markNeverNull();
	}
	removeTrivialPhi();
	}

	public void addOperands(List<Value> operands) {
	// Phi operands are only filled in once to complete the phi. Some phis are incomplete for a
	// period of time to break cycles. When the cycle has been resolved they are completed
	// exactly once by adding the operands.
	assert this.operands.isEmpty();
	boolean canBeNull = false;
	if (operands.size() == 0) {
	throwUndefinedValueError();
	}
	for (Value operand : operands) {
	canBeNull \|= operand.canBeNull();
	appendOperand(operand);
	}
	if (!canBeNull) {
	markNeverNull();
	}
	removeTrivialPhi();
	}

	private void throwUndefinedValueError() {
	throw new CompilationError(
	"Undefined value encountered during compilation. "
	+ "This is typically caused by invalid dex input that uses a register "
	+ "that is not define on all control-flow paths leading to the use.");
	}

	private void appendOperand(Value operand) {
	operands.add(operand);
	operand.addPhiUser(this);
	}

	public Value getOperand(int predIndex) {
	return operands.get(predIndex);
	}

	public List<Value> getOperands() {
	return operands;
	}

	public void removeOperand(int index) {
	operands.get(index).removePhiUser(this);
	operands.remove(index);
	}

	public void removeOperandsByIndex(List<Integer> operandsToRemove) {
	if (operandsToRemove.isEmpty()) {
	return;
	}
	List<Value> copy = new ArrayList<>(operands);
	operands.clear();
	int current = 0;
	for (int i : operandsToRemove) {
	operands.addAll(copy.subList(current, i));
	copy.get(i).removePhiUser(this);
	current = i + 1;
	}
	operands.addAll(copy.subList(current, copy.size()));
	}

	public void replace(int predIndex, Value newValue) {
	Value current = operands.get(predIndex);
	operands.set(predIndex, newValue);
	newValue.addPhiUser(this);
	current.removePhiUser(this);
	}

	// Removing the phi user from the current value leads to concurrent modification errors
	// during trivial phi elimination. It is safe to not remove the phi user from current
	// since current will be unreachable after trivial phi elimination.
	// TODO(ager): can we unify the these replace methods and avoid the concurrent modification
	// issue?
	private void replaceTrivialPhi(Value current, Value newValue) {
	for (int i = 0; i < operands.size(); i++) {
	if (operands.get(i) == current) {
	operands.set(i, newValue);
	newValue.addPhiUser(this);
	}
	}
	}

	public boolean isTrivialPhi() {
	Value same = null;
	for (Value op : operands) {
	if (op == same \|\| op == this) {
	// Have only seen one value other than this.
	continue;
	}
	if (same != null) {
	// Merged at least two values and is therefore not trivial.
	return false;
	}
	same = op;
	}
	return true;
	}

	public void removeTrivialPhi() {
	Value same = null;
	for (Value op : operands) {
	if (op == same \|\| op == this) {
	// Have only seen one value other than this.
	continue;
	}
	if (same != null) {
	// Merged at least two values and is therefore not trivial.
	assert !isTrivialPhi();
	return;
	}
	same = op;
	}
	assert isTrivialPhi();
	// Removing this phi, so get rid of it as a phi user from all of the operands to avoid
	// recursively getting back here with the same phi. If the phi has itself as an operand
	// that also removes the self-reference.
	for (Value op : operands) {
	op.removePhiUser(this);
	}
	// Replace this phi with the unique value in all users.
	for (Instruction user : uniqueUsers()) {
	user.replaceValue(this, same);
	}
	for (Phi user : uniquePhiUsers()) {
	user.replaceTrivialPhi(this, same);
	}
	if (debugUsers() != null) {
	for (Instruction user : debugUsers()) {
	user.replaceDebugPhi(this, same);
	}
	}
	// If IR construction is taking place, update the definition users.
	if (definitionUsers != null) {
	for (Map<Integer, Value> user : definitionUsers) {
	for (Map.Entry<Integer, Value> entry : user.entrySet()) {
	if (entry.getValue() == this) {
	entry.setValue(same);
	if (same.isPhi()) {
	same.asPhi().addDefinitionsUser(user);
	}
	}
	}
	}
	}
	// Try to simplify phi users that might now have become trivial.
	for (Phi user : uniquePhiUsers()) {
	user.removeTrivialPhi();
	}
	// Get rid of the phi itself.
	block.removePhi(this);
	}

	public String printPhi() {
	StringBuilder builder = new StringBuilder();
	builder.append("v");
	builder.append(number);
	if (getLocalInfo() != null) {
	builder.append("(").append(getLocalInfo()).append(")");
	}
	builder.append(" <- phi");
	StringUtils.append(builder, ListUtils.map(operands, Value::toString));
	return builder.toString();
	}

	public void print(CfgPrinter printer) {
	int uses = numberOfPhiUsers() + numberOfUsers();
	printer
	.print("0 ") // bci
	.append(uses) // use
	.append(" v").append(number) // tid
	.append(" Phi");
	for (Value operand : operands) {
	printer.append(" v").append(operand.number);
	}
	}

	public void addDefinitionsUser(Map<Integer, Value> currentDefinitions) {
	definitionUsers.add(currentDefinitions);
	}

	public void removeDefinitionsUser(Map<Integer, Value> currentDefinitions) {
	definitionUsers.remove(currentDefinitions);
	}

	public void clearDefinitionsUsers() {
	definitionUsers = null;
	}

	private boolean isSingleConstZero(Value value) {
	return value.definition != null && value.definition.isConstNumber() &&
	value.definition.asConstNumber().isZero() &&
	value.outType() == MoveType.SINGLE;
	}

	private MoveType computeOutType(Set<Phi> active) {
	if (outType != null) {
	return outType;
	}
	active.add(this);
	// Go through non-phi operands first to determine if we have an operand that dictates the type.
	for (Value operand : operands) {
	// Since a constant zero can be either an integer or an Object (null) we skip them
	// when computing types and rely on other operands to specify the actual type.
	if (!operand.isPhi() && !isSingleConstZero(operand)) {
	return operand.outType();
	}
	}
	// We did not find a non-phi operand that dictates the type. Recurse on phi arguments.
	for (Value operand : operands) {
	if (operand.isPhi() && !active.contains(operand)) {
	MoveType phiType = operand.asPhi().computeOutType(active);
	// TODO(zerny): If we had a CONST_ZERO type element, we could often avoid going through
	// all phis. We would only have to recurse until we got a non CONST_ZERO out type.
	if (phiType != MoveType.SINGLE) {
	return phiType;
	}
	}
	}
	// All operands were the constant zero or phis with out type SINGLE and the out type is either
	// object or single depending on the use. Since all inputs have out type SINGLE it is safe to
	// return MoveType.SINGLE here.
	assert type == MoveType.SINGLE \|\| type == MoveType.OBJECT;
	return MoveType.SINGLE;
	}

	@Override
	public MoveType outType() {
	if (outType != null) {
	return outType;
	}
	return computeOutType(new HashSet<>());
	}

	@Override
	public boolean isConstant() {
	return false;
	}

	public boolean needsRegister() {
	return true;
	}
	}