Mercurial > hg > truffle
view graal/GraalCompiler/src/com/sun/c1x/alloc/EdgeMoveOptimizer.java @ 2630:c93adece95d2
Small clean up.
author | Thomas Wuerthinger <thomas@wuerthinger.net> |
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date | Tue, 10 May 2011 16:47:49 +0200 |
parents | 16b9a8b5ad39 |
children | 6ab73784566a |
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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.sun.c1x.alloc; import java.util.*; import com.sun.c1x.*; import com.sun.c1x.ir.*; import com.sun.c1x.lir.*; /** * This class optimizes moves, particularly those that result from eliminating SSA form. * * When a block has more than one predecessor, and all predecessors end with * the {@linkplain #same(LIRInstruction, LIRInstruction) same} sequence of * {@linkplain LIROpcode#Move move} instructions, then these sequences * can be replaced with a single copy of the sequence at the beginning of the block. * * Similarly, when a block has more than one successor, then same sequences of * moves at the beginning of the successors can be placed once at the end of * the block. But because the moves must be inserted before all branch * instructions, this works only when there is exactly one conditional branch * at the end of the block (because the moves must be inserted before all * branches, but after all compares). * * This optimization affects all kind of moves (reg->reg, reg->stack and * stack->reg). Because this optimization works best when a block contains only * a few moves, it has a huge impact on the number of blocks that are totally * empty. * * @author Christian Wimmer (original HotSpot implementation) * @author Thomas Wuerthinger * @author Doug Simon */ final class EdgeMoveOptimizer { /** * Optimizes moves on block edges. * * @param blockList a list of blocks whose moves should be optimized */ public static void optimize(List<BlockBegin> blockList) { EdgeMoveOptimizer optimizer = new EdgeMoveOptimizer(); // ignore the first block in the list (index 0 is not processed) for (int i = blockList.size() - 1; i >= 1; i--) { BlockBegin block = blockList.get(i); if (block.numberOfPreds() > 1 && !block.checkBlockFlag(BlockBegin.BlockFlag.ExceptionEntry)) { optimizer.optimizeMovesAtBlockEnd(block); } if (block.numberOfSux() == 2) { optimizer.optimizeMovesAtBlockBegin(block); } } } private final List<List<LIRInstruction>> edgeInstructionSeqences; private EdgeMoveOptimizer() { edgeInstructionSeqences = new ArrayList<List<LIRInstruction>>(4); } /** * Determines if two operations are both {@linkplain LIROpcode#Move moves} * that have the same {@linkplain LIROp1#operand() source} and {@linkplain LIROp1#result() destination} * operands and they have the same {@linkplain LIRInstruction#info debug info}. * * @param op1 the first instruction to compare * @param op2 the second instruction to compare * @return {@code true} if {@code op1} and {@code op2} are the same by the above algorithm */ private boolean same(LIRInstruction op1, LIRInstruction op2) { assert op1 != null; assert op2 != null; if (op1.code == LIROpcode.Move && op2.code == LIROpcode.Move) { assert op1 instanceof LIROp1 : "move must be LIROp1"; assert op2 instanceof LIROp1 : "move must be LIROp1"; LIROp1 move1 = (LIROp1) op1; LIROp1 move2 = (LIROp1) op2; if (move1.info == move2.info && move1.operand().equals(move2.operand()) && move1.result().equals(move2.result())) { // these moves are exactly equal and can be optimized return true; } } return false; } /** * Moves the longest {@linkplain #same common} subsequence at the end all * predecessors of {@code block} to the start of {@code block}. */ private void optimizeMovesAtBlockEnd(BlockBegin block) { if (block.isPredecessor(block)) { // currently we can't handle this correctly. return; } // clear all internal data structures edgeInstructionSeqences.clear(); int numPreds = block.numberOfPreds(); assert numPreds > 1 : "do not call otherwise"; assert !block.checkBlockFlag(BlockBegin.BlockFlag.ExceptionEntry) : "exception handlers not allowed"; // setup a list with the LIR instructions of all predecessors for (int i = 0; i < numPreds; i++) { BlockBegin pred = block.predAt(i); List<LIRInstruction> predInstructions = pred.lir().instructionsList(); if (pred.numberOfSux() != 1) { // this can happen with switch-statements where multiple edges are between // the same blocks. return; } assert pred.suxAt(0) == block : "invalid control flow"; assert predInstructions.get(predInstructions.size() - 1).code == LIROpcode.Branch : "block with successor must end with branch"; assert predInstructions.get(predInstructions.size() - 1) instanceof LIRBranch : "branch must be LIROpBranch"; assert ((LIRBranch) predInstructions.get(predInstructions.size() - 1)).cond() == Condition.TRUE : "block must end with unconditional branch"; if (predInstructions.get(predInstructions.size() - 1).info != null) { // can not optimize instructions that have debug info return; } // ignore the unconditional branch at the end of the block List<LIRInstruction> seq = predInstructions.subList(0, predInstructions.size() - 1); edgeInstructionSeqences.add(seq); } // process lir-instructions while all predecessors end with the same instruction while (true) { List<LIRInstruction> seq = edgeInstructionSeqences.get(0); if (seq.isEmpty()) { return; } LIRInstruction op = last(seq); for (int i = 1; i < numPreds; ++i) { List<LIRInstruction> otherSeq = edgeInstructionSeqences.get(i); if (otherSeq.isEmpty() || !same(op, last(otherSeq))) { return; } } // insert the instruction at the beginning of the current block block.lir().insertBefore(1, op); // delete the instruction at the end of all predecessors for (int i = 0; i < numPreds; i++) { seq = edgeInstructionSeqences.get(i); removeLast(seq); } } } /** * Moves the longest {@linkplain #same common} subsequence at the start of all * successors of {@code block} to the end of {@code block} just prior to the * branch instruction ending {@code block}. */ private void optimizeMovesAtBlockBegin(BlockBegin block) { edgeInstructionSeqences.clear(); int numSux = block.numberOfSux(); List<LIRInstruction> instructions = block.lir().instructionsList(); assert numSux == 2 : "method should not be called otherwise"; assert instructions.get(instructions.size() - 1).code == LIROpcode.Branch : "block with successor must end with branch"; assert instructions.get(instructions.size() - 1) instanceof LIRBranch : "branch must be LIROpBranch"; assert ((LIRBranch) instructions.get(instructions.size() - 1)).cond() == Condition.TRUE : "block must end with unconditional branch"; if (instructions.get(instructions.size() - 1).info != null) { // cannot optimize instructions when debug info is needed return; } LIRInstruction branch = instructions.get(instructions.size() - 2); if (branch.info != null || (branch.code != LIROpcode.Branch && branch.code != LIROpcode.CondFloatBranch)) { // not a valid case for optimization // currently, only blocks that end with two branches (conditional branch followed // by unconditional branch) are optimized return; } // now it is guaranteed that the block ends with two branch instructions. // the instructions are inserted at the end of the block before these two branches int insertIdx = instructions.size() - 2; if (C1XOptions.DetailedAsserts) { for (int i = insertIdx - 1; i >= 0; i--) { LIRInstruction op = instructions.get(i); if ((op.code == LIROpcode.Branch || op.code == LIROpcode.CondFloatBranch) && ((LIRBranch) op).block() != null) { throw new Error("block with two successors can have only two branch instructions"); } } } // setup a list with the lir-instructions of all successors for (int i = 0; i < numSux; i++) { BlockBegin sux = block.suxAt(i); List<LIRInstruction> suxInstructions = sux.lir().instructionsList(); assert suxInstructions.get(0).code == LIROpcode.Label : "block must start with label"; if (sux.numberOfPreds() != 1) { // this can happen with switch-statements where multiple edges are between // the same blocks. return; } assert sux.predAt(0) == block : "invalid control flow"; assert !sux.checkBlockFlag(BlockBegin.BlockFlag.ExceptionEntry) : "exception handlers not allowed"; // ignore the label at the beginning of the block List<LIRInstruction> seq = suxInstructions.subList(1, suxInstructions.size()); edgeInstructionSeqences.add(seq); } // process LIR instructions while all successors begin with the same instruction while (true) { List<LIRInstruction> seq = edgeInstructionSeqences.get(0); if (seq.isEmpty()) { return; } LIRInstruction op = first(seq); for (int i = 1; i < numSux; i++) { List<LIRInstruction> otherSeq = edgeInstructionSeqences.get(i); if (otherSeq.isEmpty() || !same(op, first(otherSeq))) { // these instructions are different and cannot be optimized . // no further optimization possible return; } } // insert instruction at end of current block block.lir().insertBefore(insertIdx, op); insertIdx++; // delete the instructions at the beginning of all successors for (int i = 0; i < numSux; i++) { seq = edgeInstructionSeqences.get(i); removeFirst(seq); } } } /** * Gets the first element from a LIR instruction sequence. */ private static LIRInstruction first(List<LIRInstruction> seq) { return seq.get(0); } /** * Gets the last element from a LIR instruction sequence. */ private static LIRInstruction last(List<LIRInstruction> seq) { return seq.get(seq.size() - 1); } /** * Removes the first element from a LIR instruction sequence. */ private static void removeFirst(List<LIRInstruction> seq) { seq.remove(0); } /** * Removes the last element from a LIR instruction sequence. */ private static void removeLast(List<LIRInstruction> seq) { seq.remove(seq.size() - 1); } }