Mercurial > hg > graal-compiler
view graal/GraalCompiler/src/com/sun/c1x/alloc/ControlFlowOptimizer.java @ 2805:c3f64b66fc78
Towards removing the next pointer from Constant and ArithmeticOp
author | Thomas Wuerthinger <thomas@wuerthinger.net> |
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date | Fri, 27 May 2011 19:57:56 +0200 |
parents | 2ac7b30b7290 |
children |
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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.graph.*; import com.sun.c1x.ir.*; import com.sun.c1x.lir.*; import com.sun.c1x.util.*; import com.sun.cri.ci.*; /** * This class performs basic optimizations on the control flow graph after LIR generation. */ final class ControlFlowOptimizer { /** * Performs control flow optimizations on the given IR graph. * @param ir the IR graph that should be optimized */ public static void optimize(IR ir) { ControlFlowOptimizer optimizer = new ControlFlowOptimizer(ir); List<LIRBlock> code = ir.linearScanOrder(); optimizer.reorderShortLoops(code); optimizer.deleteEmptyBlocks(code); optimizer.deleteUnnecessaryJumps(code); optimizer.deleteJumpsToReturn(code); } private final IR ir; private ControlFlowOptimizer(IR ir) { this.ir = ir; } private void reorderShortLoop(List<LIRBlock> code, LIRBlock headerBlock, int headerIdx) { int i = headerIdx + 1; int maxEnd = Math.min(headerIdx + C1XOptions.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 this successor private boolean canDeleteBlock(LIRBlock block) { if (block.numberOfSux() != 1 || block == ir.startBlock || block.suxAt(0) == block) { return false; } List<LIRInstruction> instructions = block.lir().instructionsList(); assert instructions.size() >= 2 : "block must have label and branch"; assert instructions.get(0).code == LIROpcode.Label : "first instruction must always be a label"; assert instructions.get(instructions.size() - 1) instanceof LIRBranch : "last instruction must always be a branch but is " + instructions.get(instructions.size() - 1); assert ((LIRBranch) instructions.get(instructions.size() - 1)).cond() == Condition.TRUE : "branch must be unconditional"; assert ((LIRBranch) instructions.get(instructions.size() - 1)).block() == block.suxAt(0) : "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<LIRBlock> code) { int oldPos = 0; int newPos = 0; int numBlocks = code.size(); while (oldPos < numBlocks) { LIRBlock block = code.get(oldPos); if (canDeleteBlock(block)) { LIRBlock newTarget = block.suxAt(0); // update the block references in any branching LIR instructions for (LIRBlock pred : block.blockPredecessors()) { for (LIRInstruction instr : pred.lir().instructionsList()) { if (instr instanceof LIRBranch) { ((LIRBranch) instr).substitute(block, newTarget); } else if (instr instanceof LIRTableSwitch) { ((LIRTableSwitch) instr).substitute(block, newTarget); } } } // adjust successor and predecessor lists block.replaceWith(newTarget); C1XMetrics.BlocksDeleted++; } 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 void deleteUnnecessaryJumps(List<LIRBlock> code) { // skip the last block because there a branch is always necessary for (int i = code.size() - 2; i >= 0; i--) { LIRBlock block = code.get(i); List<LIRInstruction> instructions = block.lir().instructionsList(); LIRInstruction lastOp = instructions.get(instructions.size() - 1); if (lastOp.code == LIROpcode.Branch) { assert lastOp instanceof LIRBranch : "branch must be of type LIRBranch"; LIRBranch lastBranch = (LIRBranch) lastOp; assert lastBranch.block() != null : "last branch must always have a block as target"; assert lastBranch.label() == lastBranch.block().label() : "must be equal"; if (lastBranch.info == null) { if (lastBranch.block() == code.get(i + 1)) { // delete last branch instruction Util.truncate(instructions, instructions.size() - 1); } else { LIRInstruction prevOp = instructions.get(instructions.size() - 2); if (prevOp.code == LIROpcode.Branch || prevOp.code == LIROpcode.CondFloatBranch) { assert prevOp instanceof LIRBranch : "branch must be of type LIRBranch"; LIRBranch prevBranch = (LIRBranch) prevOp; if (prevBranch.block() == code.get(i + 1) && prevBranch.info == null) { // eliminate a conditional branch to the immediate successor prevBranch.changeBlock(lastBranch.block()); prevBranch.negateCondition(); Util.truncate(instructions, instructions.size() - 1); } } } } } } assert verify(code); } private void deleteJumpsToReturn(List<LIRBlock> code) { for (int i = code.size() - 1; i >= 0; i--) { LIRBlock block = code.get(i); List<LIRInstruction> curInstructions = block.lir().instructionsList(); LIRInstruction curLastOp = curInstructions.get(curInstructions.size() - 1); assert curInstructions.get(0).code == LIROpcode.Label : "first instruction must always be a label"; if (curInstructions.size() == 2 && curLastOp.code == LIROpcode.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"; assert curLastOp instanceof LIROp1 : "return must be LIROp1"; CiValue returnOpr = ((LIROp1) curLastOp).operand(); for (int j = block.numberOfPreds() - 1; j >= 0; j--) { LIRBlock pred = block.predAt(j); List<LIRInstruction> predInstructions = pred.lir().instructionsList(); LIRInstruction predLastOp = predInstructions.get(predInstructions.size() - 1); if (predLastOp.code == LIROpcode.Branch) { assert predLastOp instanceof LIRBranch : "branch must be LIRBranch"; LIRBranch predLastBranch = (LIRBranch) predLastOp; if (predLastBranch.block() == block && predLastBranch.cond() == Condition.TRUE && 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, new LIROp1(LIROpcode.Return, returnOpr)); } } } } } } private boolean verify(List<LIRBlock> code) { for (LIRBlock block : code) { List<LIRInstruction> instructions = block.lir().instructionsList(); for (LIRInstruction instr : instructions) { if (instr instanceof LIRBranch) { LIRBranch opBranch = (LIRBranch) instr; assert opBranch.block() == null || code.contains(opBranch.block()) : "missing successor branch from: " + block + " to: " + opBranch.block(); assert opBranch.unorderedBlock() == null || code.contains(opBranch.unorderedBlock()) : "missing successor branch from: " + block + " to: " + opBranch.unorderedBlock(); } } for (LIRBlock sux : block.blockSuccessors()) { assert code.contains(sux) : "missing successor from: " + block + "to: " + sux; } for (LIRBlock pred : block.blockPredecessors()) { assert code.contains(pred) : "missing predecessor from: " + block + "to: " + pred; } } return true; } }