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view graal/com.oracle.max.graal.compiler/src/com/oracle/graal/compiler/alloc/ControlFlowOptimizer.java @ 5060:4ed4295ce15f
Update import statements.
author | Thomas Wuerthinger <thomas.wuerthinger@oracle.com> |
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date | Thu, 08 Mar 2012 19:11:12 +0100 |
parents | ed559a528128 |
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/* * Copyright (c) 2009, 2011, Oracle and/or its affiliates. All rights reserved. * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. * * This code is free software; you can redistribute it and/or modify it * under the terms of the GNU General Public License version 2 only, as * published by the Free Software Foundation. * * This code is distributed in the hope that it will be useful, but WITHOUT * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License * version 2 for more details (a copy is included in the LICENSE file that * accompanied this code). * * You should have received a copy of the GNU General Public License version * 2 along with this work; if not, write to the Free Software Foundation, * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. * * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA * or visit www.oracle.com if you need additional information or have any * questions. */ package com.oracle.graal.compiler.alloc; import java.util.*; import com.oracle.graal.compiler.util.*; import com.oracle.graal.debug.*; import com.oracle.graal.lir.*; import com.oracle.graal.lir.cfg.*; /** * This class performs basic optimizations on the control flow graph after LIR generation. */ final class ControlFlowOptimizer { /** * Performs control flow optimizations on the given LIR graph. * @param ir the LIR graph that should be optimized */ public static void optimize(LIR ir) { ControlFlowOptimizer optimizer = new ControlFlowOptimizer(ir); List<Block> code = ir.codeEmittingOrder(); //optimizer.reorderShortLoops(code); optimizer.deleteEmptyBlocks(code); ControlFlowOptimizer.deleteUnnecessaryJumps(code); //ControlFlowOptimizer.deleteJumpsToReturn(code); } private final LIR ir; private ControlFlowOptimizer(LIR ir) { this.ir = ir; } /* private void reorderShortLoop(List<LIRBlock> code, LIRBlock headerBlock, int headerIdx) { int i = headerIdx + 1; int maxEnd = Math.min(headerIdx + GraalOptions.MaximumShortLoopSize, code.size()); while (i < maxEnd && code.get(i).loopDepth() >= headerBlock.loopDepth()) { i++; } if (i == code.size() || code.get(i).loopDepth() < headerBlock.loopDepth()) { int endIdx = i - 1; LIRBlock endBlock = code.get(endIdx); if (endBlock.numberOfSux() == 1 && endBlock.suxAt(0) == headerBlock) { // short loop from headerIdx to endIdx found . reorder blocks such that // the headerBlock is the last block instead of the first block of the loop for (int j = headerIdx; j < endIdx; j++) { code.set(j, code.get(j + 1)); } code.set(endIdx, headerBlock); } } }*/ /* private void reorderShortLoops(List<LIRBlock> code) { for (int i = code.size() - 1; i >= 0; i--) { LIRBlock block = code.get(i); if (block.isLinearScanLoopHeader()) { reorderShortLoop(code, block, i); } } assert verify(code); }*/ // only blocks with exactly one successor can be deleted. Such blocks // must always end with an unconditional branch to its successor private boolean canDeleteBlock(Block block) { if (block.numberOfSux() != 1 || block == ir.cfg.getStartBlock() || block.suxAt(0) == block) { return false; } List<LIRInstruction> instructions = block.lir; assert instructions.size() >= 2 : "block must have label and branch"; assert instructions.get(0) instanceof StandardOp.LabelOp : "first instruction must always be a label"; assert instructions.get(instructions.size() - 1) instanceof StandardOp.JumpOp : "last instruction must always be a branch"; assert ((StandardOp.JumpOp) instructions.get(instructions.size() - 1)).destination().label() == ((StandardOp.LabelOp) block.suxAt(0).lir.get(0)).getLabel() : "branch target must be the successor"; // block must have exactly one successor return instructions.size() == 2 && instructions.get(instructions.size() - 1).info == null; } private void deleteEmptyBlocks(List<Block> code) { int oldPos = 0; int newPos = 0; int numBlocks = code.size(); assert verify(code); while (oldPos < numBlocks) { Block block = code.get(oldPos); if (canDeleteBlock(block)) { // adjust successor and predecessor lists Block other = block.suxAt(0); for (Block pred : block.getPredecessors()) { Util.replaceAllInList(block, other, pred.getSuccessors()); } for (int i = 0; i < other.getPredecessors().size(); i++) { if (other.getPredecessors().get(i) == block) { other.getPredecessors().remove(i); other.getPredecessors().addAll(i, block.getPredecessors()); } } block.getSuccessors().clear(); block.getPredecessors().clear(); Debug.metric("BlocksDeleted").increment(); } else { // adjust position of this block in the block list if blocks before // have been deleted if (newPos != oldPos) { code.set(newPos, code.get(oldPos)); } newPos++; } oldPos++; } assert verify(code); Util.truncate(code, newPos); assert verify(code); } private static void deleteUnnecessaryJumps(List<Block> code) { // skip the last block because there a branch is always necessary for (int i = code.size() - 2; i >= 0; i--) { Block block = code.get(i); List<LIRInstruction> instructions = block.lir; LIRInstruction lastOp = instructions.get(instructions.size() - 1); if (lastOp instanceof StandardOp.JumpOp) { StandardOp.JumpOp lastJump = (StandardOp.JumpOp) lastOp; if (lastOp.info == null) { if (lastJump.destination().label() == ((StandardOp.LabelOp) code.get(i + 1).lir.get(0)).getLabel()) { // delete last branch instruction Util.truncate(instructions, instructions.size() - 1); } else { LIRInstruction prevOp = instructions.get(instructions.size() - 2); if (prevOp instanceof StandardOp.BranchOp) { StandardOp.BranchOp prevBranch = (StandardOp.BranchOp) prevOp; if (prevBranch.destination().label() == ((StandardOp.LabelOp) code.get(i + 1).lir.get(0)).getLabel() && prevOp.info == null) { // eliminate a conditional branch to the immediate successor prevBranch.negate(lastJump.destination()); Util.truncate(instructions, instructions.size() - 1); } } } } } } assert verify(code); } /* private static void deleteJumpsToReturn(List<LIRBlock> code) { for (int i = code.size() - 1; i >= 0; i--) { LIRBlock block = code.get(i); List<LIRInstruction> curInstructions = block.lir(); LIRInstruction curLastOp = curInstructions.get(curInstructions.size() - 1); assert curInstructions.get(0).code == StandardOpcode.LABEL : "first instruction must always be a label"; if (curInstructions.size() == 2 && curLastOp.code == StandardOpcode.RETURN) { // the block contains only a label and a return // if a predecessor ends with an unconditional jump to this block, then the jump // can be replaced with a return instruction // // Note: the original block with only a return statement cannot be deleted completely // because the predecessors might have other (conditional) jumps to this block. // this may lead to unnecesary return instructions in the final code assert curLastOp.info == null : "return instructions do not have debug information"; CiValue returnOpr = curLastOp.input(0); for (int j = block.numberOfPreds() - 1; j >= 0; j--) { LIRBlock pred = block.predAt(j); List<LIRInstruction> predInstructions = pred.lir(); LIRInstruction predLastOp = predInstructions.get(predInstructions.size() - 1); if (predLastOp instanceof LIRBranch) { LIRBranch predLastBranch = (LIRBranch) predLastOp; if (predLastBranch.destination().label() == block.label() && predLastBranch.code == StandardOpcode.JUMP && predLastBranch.info == null) { // replace the jump to a return with a direct return // Note: currently the edge between the blocks is not deleted predInstructions.set(predInstructions.size() - 1, StandardOpcode.RETURN.create(returnOpr)); } } } } } } */ private static boolean verify(List<Block> code) { for (Block block : code) { for (Block sux : block.getSuccessors()) { assert code.contains(sux) : "missing successor from: " + block + "to: " + sux; } for (Block pred : block.getPredecessors()) { assert code.contains(pred) : "missing predecessor from: " + block + "to: " + pred; } } return true; } }