FunctionMetrics

classFunctionMetrics

Cheap structural metrics collected in one walk over the original HIR.

All counters are structural — they depend only on the shape of the HIR tree, not on liveness or dataflow. The "bonus" fields (constLoads, moves) drive the hasOptimizationSurface gate: they let the heuristic predict whether ConstPropagationPass and MoveCoalescingPass can pay for their compile-time cost on this function.

Constructors

FunctionMetrics()

FunctionMetrics()

Properties

arithBitwise read / write

intarithBitwise

Implementation

int arithBitwise = 0;

backEdges read / write

intbackEdges

Implementation

int backEdges = 0;

blocks read / write

intblocks

Implementation

int blocks = 0;

branches read / write

intbranches

Implementation

int branches = 0;

calls read / write

intcalls

Implementation

int calls = 0;

constLoads read / write

intconstLoads

getter:

Number of LoadConst, LoadBool, and LoadNil instructions.

Functions with very few const-loads cannot benefit from ConstPropagationPass — there is nothing to fold and few RK-position operands to rewrite.

setter:

Number of LoadConst, LoadBool, and LoadNil instructions.

Functions with very few const-loads cannot benefit from ConstPropagationPass — there is nothing to fold and few RK-position operands to rewrite.

Implementation

int constLoads = 0;

hashCode no setter inherited

intgethashCode

The hash code for this object.

A hash code is a single integer which represents the state of the object that affects operator == comparisons.

All objects have hash codes. The default hash code implemented by Object represents only the identity of the object, the same way as the default operator == implementation only considers objects equal if they are identical (see identityHashCode).

If operator == is overridden to use the object state instead, the hash code must also be changed to represent that state, otherwise the object cannot be used in hash based data structures like the default Set and Map implementations.

Hash codes must be the same for objects that are equal to each other according to operator ==. The hash code of an object should only change if the object changes in a way that affects equality. There are no further requirements for the hash codes. They need not be consistent between executions of the same program and there are no distribution guarantees.

Objects that are not equal are allowed to have the same hash code. It is even technically allowed that all instances have the same hash code, but if clashes happen too often, it may reduce the efficiency of hash-based data structures like HashSet or HashMap.

If a subclass overrides hashCode, it should override the operator == operator as well to maintain consistency.

Inherited from Object.

Implementation

external int get hashCode;

hasOptimizationSurface no setter

boolgethasOptimizationSurface

Cheap "is this function likely to benefit from the v1 passes?" test.

ConstPropagationPass and MoveCoalescingPass are no-ops on functions with very few const-loads and very few Moves. Without this gate, the auto policy would spend the pass-list cost on functions whose score is driven purely by call count or back edges (e.g. one-shot initialisers and dispatch closures). The threshold values were chosen against the calibration corpus; see test/perf/compiler_opt_calibration_test.dart.

Implementation

bool get hasOptimizationSurface =>
    constLoads >= 2 || moves >= 2 || arithBitwise >= 2;

instructions read / write

intinstructions

Implementation

int instructions = 0;

moves read / write

intmoves

getter:

Number of Move instructions.

Functions with very few Moves cannot benefit from MoveCoalescingPass.

setter:

Number of Move instructions.

Functions with very few Moves cannot benefit from MoveCoalescingPass.

Implementation

int moves = 0;

runtimeType no setter inherited

TypegetruntimeType

A representation of the runtime type of the object.

Inherited from Object.

Implementation

external Type get runtimeType;

Methods

noSuchMethod() inherited

dynamicnoSuchMethod(Invocationinvocation)

Invoked when a nonexistent method or property is accessed.

A dynamic member invocation can attempt to call a member which doesn't exist on the receiving object. Example:

dynamic object = 1;
object.add(42); // Statically allowed, run-time error

This invalid code will invoke the noSuchMethod method of the integer 1 with an Invocation representing the .add(42) call and arguments (which then throws).

Classes can override noSuchMethod to provide custom behavior for such invalid dynamic invocations.

A class with a non-default noSuchMethod invocation can also omit implementations for members of its interface. Example:

class MockList<T> implements List<T> {
  noSuchMethod(Invocation invocation) {
    log(invocation);
    super.noSuchMethod(invocation); // Will throw.
  }
}
void main() {
  MockList().add(42);
}

This code has no compile-time warnings or errors even though the MockList class has no concrete implementation of any of the List interface methods. Calls to List methods are forwarded to noSuchMethod, so this code will log an invocation similar to Invocation.method(#add, [42]) and then throw.

If a value is returned from noSuchMethod, it becomes the result of the original invocation. If the value is not of a type that can be returned by the original invocation, a type error occurs at the invocation.

The default behavior is to throw a NoSuchMethodError.

Inherited from Object.

Implementation

@pragma("vm:entry-point")
@pragma("wasm:entry-point")
external dynamic noSuchMethod(Invocation invocation);

score()

intscore(HeuristicWeightsweights)

Implementation

int score(HeuristicWeights weights) {
  return instructions * weights.instructions +
      blocks * weights.blocks +
      backEdges * weights.backEdges +
      calls * weights.calls +
      branches * weights.branches +
      arithBitwise * weights.arithBitwise;
}

toString() inherited

StringtoString()

A string representation of this object.

Some classes have a default textual representation, often paired with a static parse function (like int.parse). These classes will provide the textual representation as their string representation.

Other classes have no meaningful textual representation that a program will care about. Such classes will typically override toString to provide useful information when inspecting the object, mainly for debugging or logging.

Inherited from Object.

Implementation

external String toString();

Operators

operator ==() inherited

booloperator ==(Objectother)

The equality operator.

The default behavior for all Objects is to return true if and only if this object and other are the same object.

Override this method to specify a different equality relation on a class. The overriding method must still be an equivalence relation. That is, it must be:

• Total: It must return a boolean for all arguments. It should never throw.

• Reflexive: For all objects o, o == o must be true.

• Symmetric: For all objects o1 and o2, o1 == o2 and o2 == o1 must either both be true, or both be false.

• Transitive: For all objects o1, o2, and o3, if o1 == o2 and o2 == o3 are true, then o1 == o3 must be true.

The method should also be consistent over time, so whether two objects are equal should only change if at least one of the objects was modified.

If a subclass overrides the equality operator, it should override the hashCode method as well to maintain consistency.

Inherited from Object.

Implementation

external bool operator ==(Object other);

Static Methods

collect()

FunctionMetricscollect(IrFunctionfn)

Implementation

static FunctionMetrics collect(IrFunction fn) {
  final m = FunctionMetrics();
  m.blocks = fn.blocks.length;
  for (final block in fn.blocks) {
    m.instructions += block.insts.length;
    for (final inst in block.insts) {
      if (inst is Call || inst is TailCall || inst is TForCall) {
        m.calls++;
      } else if (inst is Branch) {
        m.branches++;
        if (_isBackEdge(inst.trueBlockId, block.id)) m.backEdges++;
        if (_isBackEdge(inst.falseBlockId, block.id)) m.backEdges++;
      } else if (inst is Jump) {
        if (_isBackEdge(inst.targetBlockId, block.id)) m.backEdges++;
      } else if (inst is Goto) {
        if (_isBackEdge(inst.targetBlockId, block.id)) m.backEdges++;
      } else if (inst is LoopBack) {
        // Numeric-for back edge: always jumps to the matching FORPREP.
        m.backEdges++;
      } else if (inst is IterFor) {
        if (_isBackEdge(inst.blockId, block.id)) m.backEdges++;
      } else if (inst is BinOp && _isArithBitwise(inst.kind)) {
        m.arithBitwise++;
      } else if (inst is LoadConst || inst is LoadBool || inst is LoadNil) {
        m.constLoads++;
      } else if (inst is Move) {
        m.moves++;
      }
    }
  }
  return m;
}