Mercurial > hg > graal-jvmci-8
view graal/com.oracle.graal.lir/src/com/oracle/graal/lir/EdgeMoveOptimizer.java @ 19274:ae17c7a2f7b1
Rename LowLevel{High,Mid,Low}TierPhase LIR{High,Mid,Low}TierPhase.
author | Josef Eisl <josef.eisl@jku.at> |
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date | Wed, 11 Feb 2015 15:43:23 +0100 |
parents | 6340d851894b |
children | cb7e8c0da978 |
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/* * Copyright (c) 2009, 2012, 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.lir; import java.util.*; import com.oracle.graal.api.code.*; import com.oracle.graal.compiler.common.cfg.*; import com.oracle.graal.lir.StandardOp.MoveOp; import com.oracle.graal.lir.gen.*; import com.oracle.graal.lir.phases.*; /** * This class optimizes moves, particularly those that result from eliminating SSA form. * <p> * When a block has more than one predecessor, and all predecessors end with the * {@linkplain Optimizer#same(LIRInstruction, LIRInstruction) same} sequence of {@linkplain MoveOp * move} instructions, then these sequences can be replaced with a single copy of the sequence at * the beginning of the block. * <p> * 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). * <p> * 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. */ public final class EdgeMoveOptimizer extends LIRLowTierPhase { @Override protected <B extends AbstractBlock<B>> void run(TargetDescription target, LIRGenerationResult lirGenRes, List<B> codeEmittingOrder, List<B> linearScanOrder) { LIR ir = lirGenRes.getLIR(); Optimizer optimizer = new Optimizer(ir); List<? extends AbstractBlock<?>> blockList = ir.linearScanOrder(); // ignore the first block in the list (index 0 is not processed) for (int i = blockList.size() - 1; i >= 1; i--) { AbstractBlock<?> block = blockList.get(i); if (block.getPredecessorCount() > 1) { optimizer.optimizeMovesAtBlockEnd(block); } if (block.getSuccessorCount() == 2) { optimizer.optimizeMovesAtBlockBegin(block); } } } private static final class Optimizer { private final List<List<LIRInstruction>> edgeInstructionSeqences; private LIR ir; public Optimizer(LIR ir) { this.ir = ir; edgeInstructionSeqences = new ArrayList<>(4); } /** * Determines if two operations are both {@linkplain MoveOp moves} that have the same * {@linkplain MoveOp#getInput() source} and {@linkplain MoveOp#getResult() destination} * operands. * * @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 static boolean same(LIRInstruction op1, LIRInstruction op2) { assert op1 != null; assert op2 != null; if (op1 instanceof MoveOp && op2 instanceof MoveOp) { MoveOp move1 = (MoveOp) op1; MoveOp move2 = (MoveOp) op2; if (move1.getInput().equals(move2.getInput()) && move1.getResult().equals(move2.getResult())) { // 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(AbstractBlock<?> block) { for (AbstractBlock<?> pred : block.getPredecessors()) { if (pred == block) { // currently we can't handle this correctly. return; } } // clear all internal data structures edgeInstructionSeqences.clear(); int numPreds = block.getPredecessorCount(); assert numPreds > 1 : "do not call otherwise"; // setup a list with the LIR instructions of all predecessors for (AbstractBlock<?> pred : block.getPredecessors()) { assert pred != null; assert ir.getLIRforBlock(pred) != null; List<LIRInstruction> predInstructions = ir.getLIRforBlock(pred); if (pred.getSuccessorCount() != 1) { // this can happen with switch-statements where multiple edges are between // the same blocks. return; } assert pred.getSuccessors().iterator().next() == block : "invalid control flow"; assert predInstructions.get(predInstructions.size() - 1) instanceof StandardOp.JumpOp : "block must end with unconditional jump"; if (predInstructions.get(predInstructions.size() - 1).hasState()) { // 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 ir.getLIRforBlock(block).add(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(AbstractBlock<?> block) { edgeInstructionSeqences.clear(); int numSux = block.getSuccessorCount(); List<LIRInstruction> instructions = ir.getLIRforBlock(block); assert numSux == 2 : "method should not be called otherwise"; LIRInstruction lastInstruction = instructions.get(instructions.size() - 1); if (lastInstruction.hasState()) { // cannot optimize instructions when debug info is needed return; } LIRInstruction branch = lastInstruction; if (!(branch instanceof StandardOp.BranchOp) || branch.hasOperands()) { // Only blocks that end with a conditional branch are optimized. // In addition, a conditional branch with operands (including state) cannot // be optimized. Moving a successor instruction before such a branch may // interfere with the operands of the branch. For example, a successive move // instruction may redefine an input operand of the branch. return; } // Now it is guaranteed that the block ends with a conditional branch. // The instructions are inserted at the end of the block before the branch. int insertIdx = instructions.size() - 1; // setup a list with the lir-instructions of all successors for (AbstractBlock<?> sux : block.getSuccessors()) { List<LIRInstruction> suxInstructions = ir.getLIRforBlock(sux); assert suxInstructions.get(0) instanceof StandardOp.LabelOp : "block must start with label"; if (sux.getPredecessorCount() != 1) { // this can happen with switch-statements where multiple edges are between // the same blocks. return; } assert sux.getPredecessors().iterator().next() == block : "invalid control flow"; // 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 ir.getLIRforBlock(block).add(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); } } }