Mercurial > hg > graal-compiler
view graal/GraalCompiler/src/com/sun/c1x/ir/ComputeLinearScanOrder.java @ 2585:3e0e65161345
new node layout: Op2
author | Lukas Stadler <lukas.stadler@jku.at> |
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date | Thu, 05 May 2011 14:12:19 +0200 |
parents | 4a36a0bd6d18 |
children | 6d19b4f476db |
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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.ir; import java.util.*; import com.sun.c1x.*; import com.sun.c1x.debug.*; import com.sun.c1x.util.*; import com.sun.cri.ci.*; /** * @author Thomas Wuerthinger * */ public final class ComputeLinearScanOrder { private final int maxBlockId; // the highest blockId of a block private int numBlocks; // total number of blocks (smaller than maxBlockId) private int numLoops; // total number of loops private boolean iterativeDominators; // method requires iterative computation of dominators List<BlockBegin> linearScanOrder; // the resulting list of blocks in correct order final CiBitMap visitedBlocks; // used for recursive processing of blocks final CiBitMap activeBlocks; // used for recursive processing of blocks final CiBitMap dominatorBlocks; // temporary BitMap used for computation of dominator final int[] forwardBranches; // number of incoming forward branches for each block final List<BlockBegin> loopEndBlocks; // list of all loop end blocks collected during countEdges BitMap2D loopMap; // two-dimensional bit set: a bit is set if a block is contained in a loop final List<BlockBegin> workList; // temporary list (used in markLoops and computeOrder) // accessors for visitedBlocks and activeBlocks void initVisited() { activeBlocks.clearAll(); visitedBlocks.clearAll(); } boolean isVisited(BlockBegin b) { return visitedBlocks.get(b.blockID); } boolean isActive(BlockBegin b) { return activeBlocks.get(b.blockID); } void setVisited(BlockBegin b) { assert !isVisited(b) : "already set"; visitedBlocks.set(b.blockID); } void setActive(BlockBegin b) { assert !isActive(b) : "already set"; activeBlocks.set(b.blockID); } void clearActive(BlockBegin b) { assert isActive(b) : "not already"; activeBlocks.clear(b.blockID); } // accessors for forwardBranches void incForwardBranches(BlockBegin b) { forwardBranches[b.blockID]++; } int decForwardBranches(BlockBegin b) { return --forwardBranches[b.blockID]; } // accessors for loopMap boolean isBlockInLoop(int loopIdx, BlockBegin b) { return loopMap.at(loopIdx, b.blockID); } void setBlockInLoop(int loopIdx, BlockBegin b) { loopMap.setBit(loopIdx, b.blockID); } void clearBlockInLoop(int loopIdx, int blockId) { loopMap.clearBit(loopIdx, blockId); } // accessors for final result public List<BlockBegin> linearScanOrder() { return linearScanOrder; } public int numLoops() { return numLoops; } public ComputeLinearScanOrder(int maxBlockId, BlockBegin startBlock) { this.maxBlockId = maxBlockId; visitedBlocks = new CiBitMap(maxBlockId); activeBlocks = new CiBitMap(maxBlockId); dominatorBlocks = new CiBitMap(maxBlockId); forwardBranches = new int[maxBlockId]; loopEndBlocks = new ArrayList<BlockBegin>(8); workList = new ArrayList<BlockBegin>(8); splitCriticalEdges(); countEdges(startBlock, null); if (numLoops > 0) { markLoops(); clearNonNaturalLoops(startBlock); assignLoopDepth(startBlock); } computeOrder(startBlock); computeDominators(); printBlocks(); assert verify(); } void splitCriticalEdges() { // TODO: move critical edge splitting from IR to here } /** * Traverses the CFG to analyze block and edge info. The analysis performed is: * * 1. Count of total number of blocks. * 2. Count of all incoming edges and backward incoming edges. * 3. Number loop header blocks. * 4. Create a list with all loop end blocks. */ void countEdges(BlockBegin cur, BlockBegin parent) { if (C1XOptions.TraceLinearScanLevel >= 3) { TTY.println("Counting edges for block B%d%s", cur.blockID, parent == null ? "" : " coming from B" + parent.blockID); } assert cur.dominator() == null : "dominator already initialized"; if (isActive(cur)) { if (C1XOptions.TraceLinearScanLevel >= 3) { TTY.println("backward branch"); } assert isVisited(cur) : "block must be visited when block is active"; assert parent != null : "must have parent"; cur.setBlockFlag(BlockBegin.BlockFlag.LinearScanLoopHeader); cur.setBlockFlag(BlockBegin.BlockFlag.BackwardBranchTarget); parent.setBlockFlag(BlockBegin.BlockFlag.LinearScanLoopEnd); // When a loop header is also the start of an exception handler, then the backward branch is // an exception edge. Because such edges are usually critical edges which cannot be split, the // loop must be excluded here from processing. if (cur.checkBlockFlag(BlockBegin.BlockFlag.ExceptionEntry)) { // Make sure that dominators are correct in this weird situation iterativeDominators = true; return; } // assert parent.numberOfSux() == 1 && parent.suxAt(0) == cur : "loop end blocks must have one successor (critical edges are split)"; loopEndBlocks.add(parent); return; } // increment number of incoming forward branches incForwardBranches(cur); if (isVisited(cur)) { if (C1XOptions.TraceLinearScanLevel >= 3) { TTY.println("block already visited"); } return; } numBlocks++; setVisited(cur); setActive(cur); // recursive call for all successors int i; for (i = cur.numberOfSux() - 1; i >= 0; i--) { countEdges(cur.suxAt(i), cur); } for (i = cur.numberOfExceptionHandlers() - 1; i >= 0; i--) { countEdges(cur.exceptionHandlerAt(i), cur); } clearActive(cur); // Each loop has a unique number. // When multiple loops are nested, assignLoopDepth assumes that the // innermost loop has the lowest number. This is guaranteed by setting // the loop number after the recursive calls for the successors above // have returned. if (cur.checkBlockFlag(BlockBegin.BlockFlag.LinearScanLoopHeader)) { assert cur.loopIndex() == -1 : "cannot set loop-index twice"; if (C1XOptions.TraceLinearScanLevel >= 3) { TTY.println("Block B%d is loop header of loop %d", cur.blockID, numLoops); } cur.setLoopIndex(numLoops); numLoops++; } if (C1XOptions.TraceLinearScanLevel >= 3) { TTY.println("Finished counting edges for block B%d", cur.blockID); } } void markLoops() { if (C1XOptions.TraceLinearScanLevel >= 3) { TTY.println("----- marking loops"); } loopMap = new BitMap2D(numLoops, maxBlockId); for (int i = loopEndBlocks.size() - 1; i >= 0; i--) { BlockBegin loopEnd = loopEndBlocks.get(i); BlockBegin loopStart = loopEnd.suxAt(0); int loopIdx = loopStart.loopIndex(); if (C1XOptions.TraceLinearScanLevel >= 3) { TTY.println("Processing loop from B%d to B%d (loop %d):", loopStart.blockID, loopEnd.blockID, loopIdx); } assert loopEnd.checkBlockFlag(BlockBegin.BlockFlag.LinearScanLoopEnd) : "loop end flag must be set"; // assert loopEnd.numberOfSux() == 1 : "incorrect number of successors"; assert loopStart.checkBlockFlag(BlockBegin.BlockFlag.LinearScanLoopHeader) : "loop header flag must be set"; assert loopIdx >= 0 && loopIdx < numLoops : "loop index not set"; assert workList.isEmpty() : "work list must be empty before processing"; // add the end-block of the loop to the working list workList.add(loopEnd); setBlockInLoop(loopIdx, loopEnd); do { BlockBegin cur = workList.remove(workList.size() - 1); if (C1XOptions.TraceLinearScanLevel >= 3) { TTY.println(" processing B%d", cur.blockID); } assert isBlockInLoop(loopIdx, cur) : "bit in loop map must be set when block is in work list"; // recursive processing of all predecessors ends when start block of loop is reached if (cur != loopStart) { for (int j = cur.numberOfPreds() - 1; j >= 0; j--) { BlockBegin pred = cur.predAt(j); if (!isBlockInLoop(loopIdx, pred)) { // this predecessor has not been processed yet, so add it to work list if (C1XOptions.TraceLinearScanLevel >= 3) { TTY.println(" pushing B%d", pred.blockID); } workList.add(pred); setBlockInLoop(loopIdx, pred); } } } } while (!workList.isEmpty()); } } // check for non-natural loops (loops where the loop header does not dominate // all other loop blocks = loops with multiple entries). // such loops are ignored void clearNonNaturalLoops(BlockBegin startBlock) { for (int i = numLoops - 1; i >= 0; i--) { if (isBlockInLoop(i, startBlock)) { // loop i contains the entry block of the method. // this is not a natural loop, so ignore it if (C1XOptions.TraceLinearScanLevel >= 2) { TTY.println("Loop %d is non-natural, so it is ignored", i); } for (int blockId = maxBlockId - 1; blockId >= 0; blockId--) { clearBlockInLoop(i, blockId); } iterativeDominators = true; } } } void assignLoopDepth(BlockBegin startBlock) { if (C1XOptions.TraceLinearScanLevel >= 3) { TTY.println("----- computing loop-depth and weight"); } initVisited(); assert workList.isEmpty() : "work list must be empty before processing"; workList.add(startBlock); do { BlockBegin cur = workList.remove(workList.size() - 1); if (!isVisited(cur)) { setVisited(cur); if (C1XOptions.TraceLinearScanLevel >= 4) { TTY.println("Computing loop depth for block B%d", cur.blockID); } // compute loop-depth and loop-index for the block assert cur.loopDepth() == 0 : "cannot set loop-depth twice"; int i; int loopDepth = 0; int minLoopIdx = -1; for (i = numLoops - 1; i >= 0; i--) { if (isBlockInLoop(i, cur)) { loopDepth++; minLoopIdx = i; } } cur.setLoopDepth(loopDepth); cur.setLoopIndex(minLoopIdx); // append all unvisited successors to work list for (i = cur.numberOfSux() - 1; i >= 0; i--) { workList.add(cur.suxAt(i)); } for (i = cur.numberOfExceptionHandlers() - 1; i >= 0; i--) { workList.add(cur.exceptionHandlerAt(i)); } } } while (!workList.isEmpty()); } BlockBegin commonDominator(BlockBegin a, BlockBegin b) { assert a != null && b != null : "must have input blocks"; dominatorBlocks.clearAll(); while (a != null) { dominatorBlocks.set(a.blockID); assert a.dominator() != null || a == linearScanOrder.get(0) : "dominator must be initialized"; a = a.dominator(); } while (b != null && !dominatorBlocks.get(b.blockID)) { assert b.dominator() != null || b == linearScanOrder.get(0) : "dominator must be initialized"; b = b.dominator(); } assert b != null : "could not find dominator"; return b; } void computeDominator(BlockBegin cur, BlockBegin parent) { if (cur.dominator() == null) { if (C1XOptions.TraceLinearScanLevel >= 4) { TTY.println("DOM: initializing dominator of B%d to B%d", cur.blockID, parent.blockID); } if (cur.isExceptionEntry()) { assert parent.dominator() != null; cur.setDominator(parent.dominator()); } else { cur.setDominator(parent); } } else if (!(cur.checkBlockFlag(BlockBegin.BlockFlag.LinearScanLoopHeader) && parent.checkBlockFlag(BlockBegin.BlockFlag.LinearScanLoopEnd))) { if (C1XOptions.TraceLinearScanLevel >= 4) { TTY.println("DOM: computing dominator of B%d: common dominator of B%d and B%d is B%d", cur.blockID, parent.blockID, cur.dominator().blockID, commonDominator(cur.dominator(), parent).blockID); } assert cur.numberOfPreds() > 1 : ""; cur.setDominator(commonDominator(cur.dominator(), parent)); } } int computeWeight(BlockBegin cur) { BlockBegin singleSux = null; if (cur.numberOfSux() == 1) { singleSux = cur.suxAt(0); } // limit loop-depth to 15 bit (only for security reason, it will never be so big) int weight = (cur.loopDepth() & 0x7FFF) << 16; int curBit = 15; // this is necessary for the (very rare) case that two successive blocks have // the same loop depth, but a different loop index (can happen for endless loops // with exception handlers) if (!cur.checkBlockFlag(BlockBegin.BlockFlag.LinearScanLoopHeader)) { weight |= (1 << curBit); } curBit--; // loop end blocks (blocks that end with a backward branch) are added // after all other blocks of the loop. if (!cur.checkBlockFlag(BlockBegin.BlockFlag.LinearScanLoopEnd)) { weight |= (1 << curBit); } curBit--; // critical edge split blocks are preferred because then they have a greater // probability to be completely empty if (cur.isCriticalEdgeSplit()) { weight |= (1 << curBit); } curBit--; // exceptions should not be thrown in normal control flow, so these blocks // are added as late as possible if (!(cur.end() instanceof Throw) && (singleSux == null || !(singleSux.end() instanceof Throw))) { weight |= (1 << curBit); } curBit--; if (!(cur.end() instanceof Return) && (singleSux == null || !(singleSux.end() instanceof Return))) { weight |= (1 << curBit); } curBit--; // exceptions handlers are added as late as possible if (!cur.checkBlockFlag(BlockBegin.BlockFlag.ExceptionEntry)) { weight |= (1 << curBit); } curBit--; // guarantee that weight is > 0 weight |= 1; assert curBit >= 0 : "too many flags"; assert weight > 0 : "weight cannot become negative"; return weight; } boolean readyForProcessing(BlockBegin cur) { // Discount the edge just traveled. // When the number drops to zero, all forward branches were processed if (decForwardBranches(cur) != 0) { return false; } assert !linearScanOrder.contains(cur) : "block already processed (block can be ready only once)"; assert !workList.contains(cur) : "block already in work-list (block can be ready only once)"; return true; } void sortIntoWorkList(BlockBegin cur) { assert !workList.contains(cur) : "block already in work list"; int curWeight = computeWeight(cur); // the linearScanNumber is used to cache the weight of a block cur.setLinearScanNumber(curWeight); if (C1XOptions.StressLinearScan) { workList.add(0, cur); return; } workList.add(null); // provide space for new element int insertIdx = workList.size() - 1; while (insertIdx > 0 && workList.get(insertIdx - 1).linearScanNumber() > curWeight) { workList.set(insertIdx, workList.get(insertIdx - 1)); insertIdx--; } workList.set(insertIdx, cur); if (C1XOptions.TraceLinearScanLevel >= 3) { TTY.println("Sorted B%d into worklist. new worklist:", cur.blockID); for (int i = 0; i < workList.size(); i++) { TTY.println(String.format("%8d B%02d weight:%6x", i, workList.get(i).blockID, workList.get(i).linearScanNumber())); } } for (int i = 0; i < workList.size(); i++) { assert workList.get(i).linearScanNumber() > 0 : "weight not set"; assert i == 0 || workList.get(i - 1).linearScanNumber() <= workList.get(i).linearScanNumber() : "incorrect order in worklist"; } } void appendBlock(BlockBegin cur) { if (C1XOptions.TraceLinearScanLevel >= 3) { TTY.println("appending block B%d (weight 0x%06x) to linear-scan order", cur.blockID, cur.linearScanNumber()); } assert !linearScanOrder.contains(cur) : "cannot add the same block twice"; // currently, the linear scan order and code emit order are equal. // therefore the linearScanNumber and the weight of a block must also // be equal. cur.setLinearScanNumber(linearScanOrder.size()); linearScanOrder.add(cur); } void computeOrder(BlockBegin startBlock) { if (C1XOptions.TraceLinearScanLevel >= 3) { TTY.println("----- computing final block order"); } // the start block is always the first block in the linear scan order linearScanOrder = new ArrayList<BlockBegin>(numBlocks); appendBlock(startBlock); assert startBlock.end() instanceof Base : "start block must end with Base-instruction"; BlockBegin stdEntry = ((Base) startBlock.end()).standardEntry(); BlockBegin osrEntry = ((Base) startBlock.end()).osrEntry(); BlockBegin suxOfOsrEntry = null; if (osrEntry != null) { // special handling for osr entry: // ignore the edge between the osr entry and its successor for processing // the osr entry block is added manually below assert osrEntry.numberOfSux() == 1 : "osr entry must have exactly one successor"; assert osrEntry.suxAt(0).numberOfPreds() >= 2 : "sucessor of osr entry must have two predecessors (otherwise it is not present in normal control flow)"; suxOfOsrEntry = osrEntry.suxAt(0); decForwardBranches(suxOfOsrEntry); computeDominator(osrEntry, startBlock); iterativeDominators = true; } computeDominator(stdEntry, startBlock); // start processing with standard entry block assert workList.isEmpty() : "list must be empty before processing"; if (readyForProcessing(stdEntry)) { sortIntoWorkList(stdEntry); } else { throw new CiBailout("the stdEntry must be ready for processing (otherwise, the method has no start block)"); } do { BlockBegin cur = workList.remove(workList.size() - 1); if (cur == suxOfOsrEntry) { // the osr entry block is ignored in normal processing : it is never added to the // work list. Instead : it is added as late as possible manually here. appendBlock(osrEntry); computeDominator(cur, osrEntry); } appendBlock(cur); int i; int numSux = cur.numberOfSux(); // changed loop order to get "intuitive" order of if- and else-blocks for (i = 0; i < numSux; i++) { BlockBegin sux = cur.suxAt(i); computeDominator(sux, cur); if (readyForProcessing(sux)) { sortIntoWorkList(sux); } } numSux = cur.numberOfExceptionHandlers(); for (i = 0; i < numSux; i++) { BlockBegin sux = cur.exceptionHandlerAt(i); computeDominator(sux, cur); if (readyForProcessing(sux)) { sortIntoWorkList(sux); } } } while (workList.size() > 0); } boolean computeDominatorsIter() { boolean changed = false; int numBlocks = linearScanOrder.size(); assert linearScanOrder.get(0).dominator() == null : "must not have dominator"; assert linearScanOrder.get(0).numberOfPreds() == 0 : "must not have predecessors"; for (int i = 1; i < numBlocks; i++) { BlockBegin block = linearScanOrder.get(i); assert block.numberOfPreds() > 0; BlockBegin dominator = block.predAt(0); if (block.isExceptionEntry()) { dominator = dominator.dominator(); } int numPreds = block.numberOfPreds(); for (int j = 1; j < numPreds; j++) { BlockBegin curPred = block.predAt(j); if (block.isExceptionEntry()) { curPred = curPred.dominator(); } dominator = commonDominator(dominator, curPred); } if (dominator != block.dominator()) { if (C1XOptions.TraceLinearScanLevel >= 4) { TTY.println("DOM: updating dominator of B%d from B%d to B%d", block.blockID, block.dominator().blockID, dominator.blockID); } block.setDominator(dominator); changed = true; } } return changed; } void computeDominators() { if (C1XOptions.TraceLinearScanLevel >= 3) { TTY.println("----- computing dominators (iterative computation reqired: %b)", iterativeDominators); } // iterative computation of dominators is only required for methods with non-natural loops // and OSR-methods. For all other methods : the dominators computed when generating the // linear scan block order are correct. if (iterativeDominators) { do { if (C1XOptions.TraceLinearScanLevel >= 1) { TTY.println("DOM: next iteration of fix-point calculation"); } } while (computeDominatorsIter()); } // check that dominators are correct assert !computeDominatorsIter() : "fix point not reached"; } public void printBlocks() { if (C1XOptions.TraceLinearScanLevel >= 2) { TTY.println("----- loop information:"); for (BlockBegin cur : linearScanOrder) { TTY.print(String.format("%4d: B%02d: ", cur.linearScanNumber(), cur.blockID)); for (int loopIdx = 0; loopIdx < numLoops; loopIdx++) { TTY.print(String.format("%d = %b ", loopIdx, isBlockInLoop(loopIdx, cur))); } TTY.println(String.format(" . loopIndex: %2d, loopDepth: %2d", cur.loopIndex(), cur.loopDepth())); } } if (C1XOptions.TraceLinearScanLevel >= 1) { TTY.println("----- linear-scan block order:"); for (BlockBegin cur : linearScanOrder) { TTY.print(String.format("%4d: B%02d loop: %2d depth: %2d", cur.linearScanNumber(), cur.blockID, cur.loopIndex(), cur.loopDepth())); TTY.print(cur.isExceptionEntry() ? " ex" : " "); TTY.print(cur.isCriticalEdgeSplit() ? " ce" : " "); TTY.print(cur.checkBlockFlag(BlockBegin.BlockFlag.LinearScanLoopHeader) ? " lh" : " "); TTY.print(cur.checkBlockFlag(BlockBegin.BlockFlag.LinearScanLoopEnd) ? " le" : " "); if (cur.dominator() != null) { TTY.print(" dom: B%d ", cur.dominator().blockID); } else { TTY.print(" dom: null "); } if (cur.numberOfPreds() > 0) { TTY.print(" preds: "); for (int j = 0; j < cur.numberOfPreds(); j++) { BlockBegin pred = cur.predAt(j); TTY.print("B%d ", pred.blockID); } } if (cur.numberOfSux() > 0) { TTY.print(" sux: "); for (int j = 0; j < cur.numberOfSux(); j++) { BlockBegin sux = cur.suxAt(j); TTY.print("B%d ", sux.blockID); } } if (cur.numberOfExceptionHandlers() > 0) { TTY.print(" ex: "); for (int j = 0; j < cur.numberOfExceptionHandlers(); j++) { BlockBegin ex = cur.exceptionHandlerAt(j); TTY.print("B%d ", ex.blockID); } } TTY.println(); } } } boolean verify() { assert linearScanOrder.size() == numBlocks : "wrong number of blocks in list"; if (C1XOptions.StressLinearScan) { // blocks are scrambled when StressLinearScan is used return true; } // check that all successors of a block have a higher linear-scan-number // and that all predecessors of a block have a lower linear-scan-number // (only backward branches of loops are ignored) int i; for (i = 0; i < linearScanOrder.size(); i++) { BlockBegin cur = linearScanOrder.get(i); assert cur.linearScanNumber() == i : "incorrect linearScanNumber"; assert cur.linearScanNumber() >= 0 && cur.linearScanNumber() == linearScanOrder.indexOf(cur) : "incorrect linearScanNumber"; for (BlockBegin sux : cur.end().blockSuccessors()) { assert sux.linearScanNumber() >= 0 && sux.linearScanNumber() == linearScanOrder.indexOf(sux) : "incorrect linearScanNumber"; if (!cur.checkBlockFlag(BlockBegin.BlockFlag.LinearScanLoopEnd)) { assert cur.linearScanNumber() < sux.linearScanNumber() : "invalid order"; } if (cur.loopDepth() == sux.loopDepth()) { assert cur.loopIndex() == sux.loopIndex() || sux.checkBlockFlag(BlockBegin.BlockFlag.LinearScanLoopHeader) : "successing blocks with same loop depth must have same loop index"; } } for (BlockBegin pred : cur.blockPredecessors()) { assert pred.linearScanNumber() >= 0 && pred.linearScanNumber() == linearScanOrder.indexOf(pred) : "incorrect linearScanNumber"; if (!cur.checkBlockFlag(BlockBegin.BlockFlag.LinearScanLoopHeader)) { assert cur.linearScanNumber() > pred.linearScanNumber() : "invalid order"; } if (cur.loopDepth() == pred.loopDepth()) { assert cur.loopIndex() == pred.loopIndex() || cur.checkBlockFlag(BlockBegin.BlockFlag.LinearScanLoopHeader) : "successing blocks with same loop depth must have same loop index"; } assert cur.dominator().linearScanNumber() <= pred.linearScanNumber() : "dominator must be before predecessors"; } // check dominator if (i == 0) { assert cur.dominator() == null : "first block has no dominator"; } else { assert cur.dominator() != null : "all but first block must have dominator"; } assert cur.numberOfPreds() != 1 || cur.dominator() == cur.predAt(0) || cur.isExceptionEntry() : "Single predecessor must also be dominator"; } // check that all loops are continuous for (int loopIdx = 0; loopIdx < numLoops; loopIdx++) { int blockIdx = 0; assert !isBlockInLoop(loopIdx, linearScanOrder.get(blockIdx)) : "the first block must not be present in any loop"; // skip blocks before the loop while (blockIdx < numBlocks && !isBlockInLoop(loopIdx, linearScanOrder.get(blockIdx))) { blockIdx++; } // skip blocks of loop while (blockIdx < numBlocks && isBlockInLoop(loopIdx, linearScanOrder.get(blockIdx))) { blockIdx++; } // after the first non-loop block : there must not be another loop-block while (blockIdx < numBlocks) { assert !isBlockInLoop(loopIdx, linearScanOrder.get(blockIdx)) : "loop not continuous in linear-scan order"; blockIdx++; } } return true; } }