Linter Demo

Errors: 1

Warnings: 12

File: /home/fstrocco/Dart/dart/benchmark/compiler/lib/src/ssa/variable_allocator.dart

// Copyright (c) 2012, the Dart project authors. Please see the AUTHORS file // for details. All rights reserved. Use of this source code is governed by a // BSD-style license that can be found in the LICENSE file. part of ssa; /** * The [LiveRange] class covers a range where an instruction is live. */ class LiveRange { final int start; // [end] is not final because it can be updated due to loops. int end; LiveRange(this.start, this.end) { assert(start <= end); } String toString() => '[$start $end['; } /** * The [LiveInterval] class contains the list of ranges where an * instruction is live. */ class LiveInterval { /** * The id where the instruction is defined. */ int start; final List<LiveRange> ranges; LiveInterval() : ranges = <LiveRange>[]; // We want [HCheck] instructions to have the same name as the // instruction it checks, so both instructions should share the same // live ranges. LiveInterval.forCheck(this.start, LiveInterval checkedInterval) : ranges = checkedInterval.ranges; /** * Update all ranges that are contained in [from, to[ to * die at [to]. */ void loopUpdate(int from, int to) { for (LiveRange range in ranges) { if (from <= range.start && range.end < to) { range.end = to; } } } /** * Add a new range to this interval. */ void add(LiveRange interval) { ranges.add(interval); } /** * Returns true if one of the ranges of this interval dies at [at]. */ bool diesAt(int at) { for (LiveRange range in ranges) { if (range.end == at) return true; } return false; } String toString() { List<String> res = new List<String>(); for (final interval in ranges) res.add(interval.toString()); return '(${res.join(", ")})'; } } /** * The [LiveEnvironment] class contains the liveIn set of a basic * block. A liveIn set of a block contains the instructions that are * live when entering that block. */ class LiveEnvironment { /** * The instruction id where the basic block starts. See * [SsaLiveIntervalBuilder.instructionId]. */ int startId; /** * The instruction id where the basic block ends. */ final int endId; /** * Loop markers that will be updated once the loop header is * visited. The liveIn set of the loop header will be merged into this * environment. [loopMarkers] is a mapping from block header to the * end instruction id of the loop exit block. */ final Map<HBasicBlock, int> loopMarkers; /** * The instructions that are live in this basic block. The values of * the map contain the instruction ids where the instructions die. * It will be used when adding a range to the live interval of an * instruction. */ final Map<HInstruction, int> liveInstructions; /** * Map containing the live intervals of instructions. */ final Map<HInstruction, LiveInterval> liveIntervals; LiveEnvironment(this.liveIntervals, this.endId) : liveInstructions = new Map<HInstruction, int>(), loopMarkers = new Map<HBasicBlock, int>(); /** * Remove an instruction from the liveIn set. This method also * updates the live interval of [instruction] to contain the new * range: [id, / id contained in [liveInstructions] /]. */ void remove(HInstruction instruction, int id) { LiveInterval interval = liveIntervals.putIfAbsent( instruction, () => new LiveInterval()); int lastId = liveInstructions[instruction]; // If [lastId] is null, then this instruction is not being used. interval.add(new LiveRange(id, lastId == null ? id : lastId)); // The instruction is defined at [id]. interval.start = id; liveInstructions.remove(instruction); } /** * Add [instruction] to the liveIn set. If the instruction is not * already in the set, we save the id where it dies. */ void add(HInstruction instruction, int userId) { // Note that we are visiting the graph in post-dominator order, so // the first time we see a variable is when it dies. liveInstructions.putIfAbsent(instruction, () => userId); } /** * Merge this environment with [other]. Update the end id of * instructions in case they are different between this and [other]. */ void mergeWith(LiveEnvironment other) { other.liveInstructions.forEach((HInstruction instruction, int existingId) { // If both environments have the same instruction id of where // [instruction] dies, there is no need to update the live // interval of [instruction]. For example the if block and the // else block have the same end id for an instruction that is // being used in the join block and defined before the if/else. if (existingId == endId) return; LiveInterval range = liveIntervals.putIfAbsent( instruction, () => new LiveInterval()); range.add(new LiveRange(other.startId, existingId)); liveInstructions[instruction] = endId; }); other.loopMarkers.forEach((k, v) { loopMarkers[k] = v; }); } void addLoopMarker(HBasicBlock header, int id) { assert(!loopMarkers.containsKey(header)); loopMarkers[header] = id; } void removeLoopMarker(HBasicBlock header) { assert(loopMarkers.containsKey(header)); loopMarkers.remove(header); } bool get isEmpty => liveInstructions.isEmpty && loopMarkers.isEmpty; bool contains(HInstruction instruction) => liveInstructions.containsKey(instruction); String toString() => liveInstructions.toString(); } /** * Builds the live intervals of each instruction. The algorithm visits * the graph post-dominator tree to find the last uses of an * instruction, and computes the liveIns of each basic block. */ class SsaLiveIntervalBuilder extends HBaseVisitor { final Compiler compiler; final Set<HInstruction> generateAtUseSite; final Set<HInstruction> controlFlowOperators; /** * A counter to assign start and end ids to live ranges. The initial * value is not relevant. Note that instructionId goes downward to ease * reasoning about live ranges (the first instruction of a graph has * the lowest id). */ int instructionId = 0; /** * The liveIns of basic blocks. */ final Map<HBasicBlock, LiveEnvironment> liveInstructions; /** * The live intervals of instructions. */ final Map<HInstruction, LiveInterval> liveIntervals; SsaLiveIntervalBuilder( this.compiler, this.generateAtUseSite, this.controlFlowOperators) : liveInstructions = new Map<HBasicBlock, LiveEnvironment>(), liveIntervals = new Map<HInstruction, LiveInterval>(); void visitGraph(HGraph graph) { visitPostDominatorTree(graph); if (!liveInstructions[graph.entry].isEmpty) { compiler.internalError(CURRENT_ELEMENT_SPANNABLE, 'LiveIntervalBuilder.'); } } void markInputsAsLiveInEnvironment(HInstruction instruction, LiveEnvironment environment) { for (int i = 0, len = instruction.inputs.length; i < len; i++) { markAsLiveInEnvironment(instruction.inputs[i], environment); } } // Returns the non-HCheck instruction, or the last [HCheck] in the // check chain that is not generate at use site. // // For example: // // t1 = GeneratedAtUseSite instruction // t2 = check(t1) // t3 = check(t2) // t4 = use(t3) // t5 = use(t3) // t6 = use(t2) // // The t1 is generate-at-use site, and the live-range must thus be on t2 and // not on the checked instruction t1. // When looking for the checkedInstructionOrNonGenerateAtUseSite of t3 we must // return t2. HInstruction checkedInstructionOrNonGenerateAtUseSite(HCheck check) { var checked = check.checkedInput; while (checked is HCheck) { HInstruction next = checked.checkedInput; if (generateAtUseSite.contains(next)) break; checked = next; } return checked; } void markAsLiveInEnvironment(HInstruction instruction, LiveEnvironment environment) { if (generateAtUseSite.contains(instruction)) { markInputsAsLiveInEnvironment(instruction, environment); } else { environment.add(instruction, instructionId); // Special case the HCheck instruction to mark the actual // checked instruction live. The checked instruction and the // [HCheck] will share the same live ranges. if (instruction is HCheck) { HCheck check = instruction; HInstruction checked = checkedInstructionOrNonGenerateAtUseSite(check); if (!generateAtUseSite.contains(checked)) { environment.add(checked, instructionId); } } } } void removeFromEnvironment(HInstruction instruction, LiveEnvironment environment) { environment.remove(instruction, instructionId); // Special case the HCheck instruction to have the same live // interval as the instruction it is checking. if (instruction is HCheck) { HCheck check = instruction; HInstruction checked = checkedInstructionOrNonGenerateAtUseSite(check); if (!generateAtUseSite.contains(checked)) { liveIntervals.putIfAbsent(checked, () => new LiveInterval()); // Unconditionally force the live ranges of the HCheck to // be the live ranges of the instruction it is checking. liveIntervals[instruction] = new LiveInterval.forCheck(instructionId, liveIntervals[checked]); } } } void visitBasicBlock(HBasicBlock block) { LiveEnvironment environment = new LiveEnvironment(liveIntervals, instructionId); // If the control flow instruction in this block will actually be // inlined in the codegen in the join block, we need to make // whatever is used by that control flow instruction as live in // the join block. if (controlFlowOperators.contains(block.last)) { HIf ifInstruction = block.last; HBasicBlock joinBlock = ifInstruction.joinBlock; if (generateAtUseSite.contains(joinBlock.phis.first)) { markInputsAsLiveInEnvironment( ifInstruction, liveInstructions[joinBlock]); } } // Add to the environment the liveIn of its successor, as well as // the inputs of the phis of the successor that flow from this block. for (int i = 0; i < block.successors.length; i++) { HBasicBlock successor = block.successors[i]; LiveEnvironment successorEnv = liveInstructions[successor]; if (successorEnv != null) { environment.mergeWith(successorEnv); } else { environment.addLoopMarker(successor, instructionId); } int index = successor.predecessors.indexOf(block); for (HPhi phi = successor.phis.first; phi != null; phi = phi.next) { markAsLiveInEnvironment(phi.inputs[index], environment); } } // Iterate over all instructions to remove an instruction from the // environment and add its inputs. HInstruction instruction = block.last; while (instruction != null) { if (!generateAtUseSite.contains(instruction)) { removeFromEnvironment(instruction, environment); markInputsAsLiveInEnvironment(instruction, environment); } instructionId--; instruction = instruction.previous; } // We just remove the phis from the environment. The inputs of the // phis will be put in the environment of the predecessors. for (HPhi phi = block.phis.first; phi != null; phi = phi.next) { if (!generateAtUseSite.contains(phi)) { environment.remove(phi, instructionId); } } // Save the liveInstructions of that block. environment.startId = instructionId + 1; liveInstructions[block] = environment; // If the block is a loop header, we can remove the loop marker, // because it will just recompute the loop phis. // We also check if this loop header has any back edges. If not, // we know there is no loop marker for it. if (block.isLoopHeader() && block.predecessors.length > 1) { updateLoopMarker(block); } } void updateLoopMarker(HBasicBlock header) { LiveEnvironment env = liveInstructions[header]; int lastId = env.loopMarkers[header]; // Update all instructions that are liveIns in [header] to have a // range that covers the loop. env.liveInstructions.forEach((HInstruction instruction, int id) { LiveInterval range = env.liveIntervals.putIfAbsent( instruction, () => new LiveInterval()); range.loopUpdate(env.startId, lastId); env.liveInstructions[instruction] = lastId; }); env.removeLoopMarker(header); // Update all liveIns set to contain the liveIns of [header]. liveInstructions.forEach((HBasicBlock block, LiveEnvironment other) { if (other.loopMarkers.containsKey(header)) { env.liveInstructions.forEach((HInstruction instruction, int id) { other.liveInstructions[instruction] = id; }); other.removeLoopMarker(header); env.loopMarkers.forEach((k, v) { other.loopMarkers[k] = v; }); } }); } } /** * Represents a copy from one instruction to another. The codegen * also uses this class to represent a copy from one variable to * another. */ class Copy { final source; final destination; Copy(this.source, this.destination); String toString() => '$destination <- $source'; } /** * A copy handler contains the copies that a basic block needs to do * after executing all its instructions. */ class CopyHandler { /** * The copies from an instruction to a phi of the successor. */ final List<Copy> copies; /** * Assignments from an instruction that does not need a name (e.g. a * constant) to the phi of a successor. */ final List<Copy> assignments; CopyHandler() : copies = new List<Copy>(), assignments = new List<Copy>(); void addCopy(HInstruction source, HInstruction destination) { copies.add(new Copy(source, destination)); } void addAssignment(HInstruction source, HInstruction destination) { assignments.add(new Copy(source, destination)); } String toString() => 'Copies: $copies, assignments: $assignments'; bool get isEmpty => copies.isEmpty && assignments.isEmpty; } /** * Contains the mapping between instructions and their names for code * generation, as well as the [CopyHandler] for each basic block. */ class VariableNames { final Map<HInstruction, String> ownName; final Map<HBasicBlock, CopyHandler> copyHandlers; // Used to control heuristic that determines how local variables are declared. final Set<String> allUsedNames; /** * Name that is used as a temporary to break cycles in * parallel copies. We make sure this name is not being used * anywhere by reserving it when we allocate names for instructions. */ final String swapTemp; String getSwapTemp() { allUsedNames.add(swapTemp); return swapTemp; } VariableNames() : ownName = new Map<HInstruction, String>(), copyHandlers = new Map<HBasicBlock, CopyHandler>(), allUsedNames = new Set<String>(), swapTemp = 't0'; int get numberOfVariables => allUsedNames.length; String getName(HInstruction instruction) { return ownName[instruction]; } CopyHandler getCopyHandler(HBasicBlock block) { return copyHandlers[block]; } void addNameUsed(String name) { allUsedNames.add(name); } bool hasName(HInstruction instruction) => ownName.containsKey(instruction); void addCopy(HBasicBlock block, HInstruction source, HPhi destination) { CopyHandler handler = copyHandlers.putIfAbsent(block, () => new CopyHandler()); handler.addCopy(source, destination); } void addAssignment(HBasicBlock block, HInstruction source, HPhi destination) { CopyHandler handler = copyHandlers.putIfAbsent(block, () => new CopyHandler()); handler.addAssignment(source, destination); } } /** * Allocates variable names for instructions, making sure they don't collide. */ class VariableNamer { final VariableNames names; final Compiler compiler; final Set<String> usedNames; final List<String> freeTemporaryNames; int temporaryIndex = 0; static final RegExp regexp = new RegExp('t[0-9]+'); VariableNamer(LiveEnvironment environment, this.names, this.compiler) : usedNames = new Set<String>(), freeTemporaryNames = new List<String>() { // [VariableNames.swapTemp] is used when there is a cycle in a copy handler. // Therefore we make sure no one uses it. usedNames.add(names.swapTemp); // All liveIns instructions must have a name at this point, so we // add them to the list of used names. environment.liveInstructions.forEach((HInstruction instruction, int index) { String name = names.getName(instruction); if (name != null) { usedNames.add(name); names.addNameUsed(name); } }); } String allocateWithHint(String originalName) { int i = 0; JavaScriptBackend backend = compiler.backend; String name = backend.namer.safeVariableName(originalName); while (usedNames.contains(name)) { name = backend.namer.safeVariableName('$originalName${i++}'); } return name; } String allocateTemporary() { while (!freeTemporaryNames.isEmpty) { String name = freeTemporaryNames.removeLast(); if (!usedNames.contains(name)) return name; } String name = 't${temporaryIndex++}'; while (usedNames.contains(name)) name = 't${temporaryIndex++}'; return name; } HPhi firstPhiUserWithElement(HInstruction instruction) { for (HInstruction user in instruction.usedBy) { if (user is HPhi && user.sourceElement != null) { return user; } } return null; } String allocateName(HInstruction instruction) { String name; if (instruction is HCheck) { // Special case this instruction to use the name of its // input if it has one. var temp = instruction; do { temp = temp.checkedInput; name = names.ownName[temp]; } while (name == null && temp is HCheck); if (name != null) return addAllocatedName(instruction, name); } if (instruction.sourceElement != null) { name = allocateWithHint(instruction.sourceElement.name); } else { // We could not find an element for the instruction. If the // instruction is used by a phi, try to use the name of the phi. // Otherwise, just allocate a temporary name. HPhi phi = firstPhiUserWithElement(instruction); if (phi != null) { name = allocateWithHint(phi.sourceElement.name); } else { name = allocateTemporary(); } } return addAllocatedName(instruction, name); } String addAllocatedName(HInstruction instruction, String name) { usedNames.add(name); names.addNameUsed(name); names.ownName[instruction] = name; return name; } /** * Frees [instruction]'s name so it can be used for other instructions. */ void freeName(HInstruction instruction) { String ownName = names.ownName[instruction]; if (ownName != null) { // We check if we have already looked for temporary names // because if we haven't, chances are the temporary we allocate // in this block can match a phi with the same name in the // successor block. if (temporaryIndex != 0 && regexp.hasMatch(ownName)) { freeTemporaryNames.add(ownName); } usedNames.remove(ownName); } } } /** * Visits all blocks in the graph, sets names to instructions, and * creates the [CopyHandler] for each block. This class needs to have * the liveIns set as well as all the live intervals of instructions. * It visits the graph in dominator order, so that at each entry of a * block, the instructions in its liveIns set have names. * * When visiting a block, it goes through all instructions. For each * instruction, it frees the names of the inputs that die at that * instruction, and allocates a name to the instruction. For each phi, * it adds a copy to the CopyHandler of the corresponding predecessor. */ class SsaVariableAllocator extends HBaseVisitor { final Compiler compiler; final Map<HBasicBlock, LiveEnvironment> liveInstructions; final Map<HInstruction, LiveInterval> liveIntervals; final Set<HInstruction> generateAtUseSite; final VariableNames names; SsaVariableAllocator(this.compiler, this.liveInstructions, this.liveIntervals, this.generateAtUseSite) : this.names = new VariableNames(); void visitGraph(HGraph graph) { visitDominatorTree(graph); } void visitBasicBlock(HBasicBlock block) { VariableNamer namer = new VariableNamer( liveInstructions[block], names, compiler); block.forEachPhi((HPhi phi) { handlePhi(phi, namer); }); block.forEachInstruction((HInstruction instruction) { handleInstruction(instruction, namer); }); } /** * Returns whether [instruction] needs a name. Instructions that * have no users or that are generated at use site do not need a name. */ bool needsName(instruction) { if (instruction is HThis) return false; if (instruction is HParameterValue) return true; if (instruction.usedBy.isEmpty) return false; if (generateAtUseSite.contains(instruction)) return false; return !instruction.nonCheck().isCodeMotionInvariant(); } /** * Returns whether [instruction] dies at the instruction [at]. */ bool diesAt(HInstruction instruction, HInstruction at) { LiveInterval atInterval = liveIntervals[at]; LiveInterval instructionInterval = liveIntervals[instruction]; int start = atInterval.start; return instructionInterval.diesAt(start); } void freeUsedNamesAt(HInstruction instruction, HInstruction at, VariableNamer namer) { if (needsName(instruction)) { if (diesAt(instruction, at)) { namer.freeName(instruction); } } else if (generateAtUseSite.contains(instruction)) { // If the instruction is generated at use site, then all its // inputs may also die at [at]. for (int i = 0, len = instruction.inputs.length; i < len; i++) { HInstruction input = instruction.inputs[i]; freeUsedNamesAt(input, at, namer); } } } void handleInstruction(HInstruction instruction, VariableNamer namer) { if (generateAtUseSite.contains(instruction)) { assert(!liveIntervals.containsKey(instruction)); return; } for (int i = 0, len = instruction.inputs.length; i < len; i++) { HInstruction input = instruction.inputs[i]; freeUsedNamesAt(input, instruction, namer); } if (needsName(instruction)) { namer.allocateName(instruction); } } void handlePhi(HPhi phi, VariableNamer namer) { if (!needsName(phi)) return; for (int i = 0; i < phi.inputs.length; i++) { HInstruction input = phi.inputs[i]; HBasicBlock predecessor = phi.block.predecessors[i]; // A [HTypeKnown] instruction never has a name, but its checked // input might, therefore we need to do a copy instead of an // assignment. while (input is HTypeKnown) input = input.inputs[0]; if (!needsName(input)) { names.addAssignment(predecessor, input, phi); } else { names.addCopy(predecessor, input, phi); } } namer.allocateName(phi); } }