OR_OR_Expression.java

/*******************************************************************************
 * Copyright (c) 2000, 2004 IBM Corporation and others.
 * All rights reserved. This program and the accompanying materials 
 * are made available under the terms of the Common Public License v1.0
 * which accompanies this distribution, and is available at
 * http://www.eclipse.org/legal/cpl-v10.html
 * 
 * Contributors:
 *     IBM Corporation - initial API and implementation
 *******************************************************************************/
package org.eclipse.jdt.internal.compiler.ast;

import org.eclipse.jdt.internal.compiler.ASTVisitor;
import org.eclipse.jdt.internal.compiler.impl.*;
import org.eclipse.jdt.internal.compiler.codegen.*;
import org.eclipse.jdt.internal.compiler.flow.*;
import org.eclipse.jdt.internal.compiler.lookup.*;

//dedicated treatment for the ||
public class OR_OR_Expression extends BinaryExpression {

	int rightInitStateIndex = -1;
	int mergedInitStateIndex = -1;

	public OR_OR_Expression(Expression left, Expression right, int operator) {
		super(left, right, operator);
	}

	public FlowInfo analyseCode(
		BlockScope currentScope,
		FlowContext flowContext,
		FlowInfo flowInfo) {

		Constant cst = this.left.optimizedBooleanConstant();
		boolean isLeftOptimizedTrue = cst != NotAConstant && cst.booleanValue() == true;
		boolean isLeftOptimizedFalse = cst != NotAConstant && cst.booleanValue() == false;

		if (isLeftOptimizedFalse) {
			// FALSE || anything
			 // need to be careful of scenario:
			//		(x || y) || !z, if passing the left info to the right, it would be swapped by the !
			FlowInfo mergedInfo = left.analyseCode(currentScope, flowContext, flowInfo).unconditionalInits();
			mergedInfo = right.analyseCode(currentScope, flowContext, mergedInfo);
			mergedInitStateIndex =
				currentScope.methodScope().recordInitializationStates(mergedInfo);
			return mergedInfo;
		}

		FlowInfo leftInfo = left.analyseCode(currentScope, flowContext, flowInfo);
	
		 // need to be careful of scenario:
		//		(x || y) || !z, if passing the left info to the right, it would be swapped by the !
		FlowInfo rightInfo = leftInfo.initsWhenFalse().unconditionalInits().copy();
		rightInitStateIndex =
			currentScope.methodScope().recordInitializationStates(rightInfo);

		int previousMode = rightInfo.reachMode();
		if (isLeftOptimizedTrue){
			rightInfo.setReachMode(FlowInfo.UNREACHABLE); 
		}
		rightInfo = right.analyseCode(currentScope, flowContext, rightInfo);
		FlowInfo falseMergedInfo = rightInfo.initsWhenFalse().copy();
		rightInfo.setReachMode(previousMode); // reset after falseMergedInfo got extracted

		FlowInfo mergedInfo = FlowInfo.conditional(
					// merging two true initInfos for such a negative case: if ((t && (b = t)) || f) r = b; // b may not have been initialized
					leftInfo.initsWhenTrue().copy().unconditionalInits().mergedWith(
						rightInfo.initsWhenTrue().copy().unconditionalInits()),
					falseMergedInfo);
		mergedInitStateIndex =
			currentScope.methodScope().recordInitializationStates(mergedInfo);
		return mergedInfo;
	}

	/**
	 * Code generation for a binary operation
	 */
	public void generateCode(BlockScope currentScope, CodeStream codeStream, boolean valueRequired) {

		int pc = codeStream.position;
		if (constant != Constant.NotAConstant) {
			// inlined value
			if (valueRequired)
				codeStream.generateConstant(constant, implicitConversion);
			codeStream.recordPositionsFrom(pc, this.sourceStart);
			return;
		}
		Constant cst = right.constant;
		if (cst != NotAConstant) {
			// <expr> || true --> true
			if (cst.booleanValue() == true) {
				this.left.generateCode(currentScope, codeStream, false);
				if (valueRequired) codeStream.iconst_1();
			} else {
				// <expr>|| false --> <expr>
				this.left.generateCode(currentScope, codeStream, valueRequired);
			}
			if (mergedInitStateIndex != -1) {
				codeStream.removeNotDefinitelyAssignedVariables(currentScope, mergedInitStateIndex);
			}			
			codeStream.generateImplicitConversion(implicitConversion);
			codeStream.updateLastRecordedEndPC(codeStream.position);
			codeStream.recordPositionsFrom(pc, this.sourceStart);
			return;
		}
		
		Label trueLabel = new Label(codeStream), endLabel;
		cst = left.optimizedBooleanConstant();
		boolean leftIsConst = cst != NotAConstant;
		boolean leftIsTrue = leftIsConst && cst.booleanValue() == true;

		cst = right.optimizedBooleanConstant();
		boolean rightIsConst = cst != NotAConstant;
		boolean rightIsTrue = rightIsConst && cst.booleanValue() == true;

		generateOperands : {
			if (leftIsConst) {
				left.generateCode(currentScope, codeStream, false);
				if (leftIsTrue) {
					break generateOperands; // no need to generate right operand
				}
			} else {
				left.generateOptimizedBoolean(currentScope, codeStream, trueLabel, null, true); 
				// need value, e.g. if (a == 1 || ((b = 2) > 0)) {} -> shouldn't initialize 'b' if a==1 
			}
			if (rightInitStateIndex != -1) {
				codeStream.addDefinitelyAssignedVariables(currentScope, rightInitStateIndex);
			}
			if (rightIsConst) {
				right.generateCode(currentScope, codeStream, false);
			} else {
				right.generateOptimizedBoolean(currentScope, codeStream, trueLabel, null, valueRequired);
			}
		}
		if (mergedInitStateIndex != -1) {
			codeStream.removeNotDefinitelyAssignedVariables(currentScope, mergedInitStateIndex);
		}
		/*
		 * improving code gen for such a case: boolean b = i < 0 || true since
		 * the label has never been used, we have the inlined value on the
		 * stack.
		 */
		if (valueRequired) {
			if (leftIsConst && leftIsTrue) {
				codeStream.iconst_1();
				codeStream.updateLastRecordedEndPC(codeStream.position);
			} else {
				if (rightIsConst && rightIsTrue) {
					codeStream.iconst_1();
					codeStream.updateLastRecordedEndPC(codeStream.position);
				} else {
					codeStream.iconst_0();
				}
				if (trueLabel.hasForwardReferences()) {
					if ((bits & ValueForReturnMASK) != 0) {
						codeStream.ireturn();
						trueLabel.place();
						codeStream.iconst_1();
					} else {
						codeStream.goto_(endLabel = new Label(codeStream));
						codeStream.decrStackSize(1);
						trueLabel.place();
						codeStream.iconst_1();
						endLabel.place();
					}
				} else {
					trueLabel.place();
				}
			}
			codeStream.generateImplicitConversion(implicitConversion);
			codeStream.updateLastRecordedEndPC(codeStream.position);
		} else {
			trueLabel.place();
		}
	}

	/**
	 * Boolean operator code generation Optimized operations are: ||
	 */
	public void generateOptimizedBoolean(BlockScope currentScope, CodeStream codeStream, Label trueLabel, Label falseLabel, boolean valueRequired) {

		if (constant != Constant.NotAConstant) {
			super.generateOptimizedBoolean(currentScope, codeStream, trueLabel, falseLabel, valueRequired);
			return;
		}

		// <expr> || false --> <expr>
		Constant cst = right.constant;
		if (cst != NotAConstant && cst.booleanValue() == false) {
			int pc = codeStream.position;
			this.left.generateOptimizedBoolean(currentScope, codeStream, trueLabel, falseLabel, valueRequired);
			if (mergedInitStateIndex != -1) {
				codeStream.removeNotDefinitelyAssignedVariables(currentScope, mergedInitStateIndex);
			}			
			codeStream.recordPositionsFrom(pc, this.sourceStart);
			return;
		}
	
		cst = left.optimizedBooleanConstant();
		boolean leftIsConst = cst != NotAConstant;
		boolean leftIsTrue = leftIsConst && cst.booleanValue() == true;

		cst = right.optimizedBooleanConstant();
		boolean rightIsConst = cst != NotAConstant;
		boolean rightIsTrue = rightIsConst && cst.booleanValue() == true;

		// default case
		generateOperands : {
			if (falseLabel == null) {
				if (trueLabel != null) {
					// implicit falling through the FALSE case
					left.generateOptimizedBoolean(currentScope, codeStream, trueLabel, null, !leftIsConst); 
					// need value, e.g. if (a == 1 || ((b = 2) > 0)) {} -> shouldn't initialize 'b' if a==1
					if (leftIsConst && leftIsTrue) {
						codeStream.goto_(trueLabel);
						codeStream.updateLastRecordedEndPC(codeStream.position);
						break generateOperands; // no need to generate right operand
					}
					if (rightInitStateIndex != -1) {
						codeStream
								.addDefinitelyAssignedVariables(currentScope, rightInitStateIndex);
					}
					right.generateOptimizedBoolean(currentScope, codeStream, trueLabel, null, valueRequired && !rightIsConst);
					if (valueRequired && rightIsConst && rightIsTrue) {
						codeStream.goto_(trueLabel);
						codeStream.updateLastRecordedEndPC(codeStream.position);
					}
				}
			} else {
				// implicit falling through the TRUE case
				if (trueLabel == null) {
					Label internalTrueLabel = new Label(codeStream);
					left.generateOptimizedBoolean(currentScope, codeStream, internalTrueLabel, null, !leftIsConst); 
					// need value, e.g. if (a == 1 || ((b = 2) > 0)) {} -> shouldn't initialize 'b' if a==1
					if (leftIsConst && leftIsTrue) {
						internalTrueLabel.place();
						break generateOperands; // no need to generate right operand
					}
					if (rightInitStateIndex != -1) {
						codeStream
								.addDefinitelyAssignedVariables(currentScope, rightInitStateIndex);
					}
					right.generateOptimizedBoolean(currentScope, codeStream, null, falseLabel, valueRequired && !rightIsConst);
					if (valueRequired && rightIsConst) {
						if (!rightIsTrue) {
							codeStream.goto_(falseLabel);
							codeStream.updateLastRecordedEndPC(codeStream.position);
						}
					}
					internalTrueLabel.place();
				} else {
					// no implicit fall through TRUE/FALSE --> should never occur
				}
			}
		}
		if (mergedInitStateIndex != -1) {
			codeStream.removeNotDefinitelyAssignedVariables(currentScope, mergedInitStateIndex);
		}
	}
	
	public boolean isCompactableOperation() {
		return false;
	}

	public void traverse(ASTVisitor visitor, BlockScope scope) {
		if (visitor.visit(this, scope)) {
			left.traverse(visitor, scope);
			right.traverse(visitor, scope);
		}
		visitor.endVisit(this, scope);
	}
}