Mercurial > hg > graal-compiler
diff graal/GraalCompiler/src/com/sun/c1x/alloc/EdgeMoveOptimizer.java @ 2509:16b9a8b5ad39
Renamings Runtime=>GraalRuntime and Compiler=>GraalCompiler
author | Thomas Wuerthinger <thomas@wuerthinger.net> |
---|---|
date | Wed, 27 Apr 2011 11:50:44 +0200 |
parents | graal/Compiler/src/com/sun/c1x/alloc/EdgeMoveOptimizer.java@9ec15d6914ca |
children | 6ab73784566a |
line wrap: on
line diff
--- /dev/null Thu Jan 01 00:00:00 1970 +0000 +++ b/graal/GraalCompiler/src/com/sun/c1x/alloc/EdgeMoveOptimizer.java Wed Apr 27 11:50:44 2011 +0200 @@ -0,0 +1,298 @@ +/* + * 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); + } +}