JIT Optimization Outcomes

In This Article
  1. General Outcomes
    1. GenericFailure
    2. GenericSuccess
    3. Disabled
    4. NoTypeInfo
    5. NoAnalysisInfo
    6. NoShapeInfo
    7. UnknownObject
    8. UnknownProperties
    9. Singleton
    10. NotSingleton
    11. NotFixedSlot
    12. InconsistentFixedSlot
    13. NotObject
    14. NotStruct
    15. NotUnboxed
    16. UnboxedConvertedToNative
    17. StructNoField
    18. InconsistentFieldType
    19. InconsistentFieldOffset
    20. NeedsTypeBarrier
    21. InDictionaryMode
    22. NoProtoFound
    23. MultiProtoPaths
    24. NonWritableProperty
    25. ProtoIndexedProps
    26. ArrayBadFlags
    27. ArrayDoubleConversion
    28. ArrayRange
    29. ArraySeenNegativeIndex
    30. TypedObjectNeutered
    31. TypedObjectArrayRange
    32. AccessNotDense
    33. AccessNotSimdObject
    34. AccessNotTypedObject
    35. AccessNotTypedArray
    36. AccessNotString
    37. StaticTypedArrayUint32
    38. StaticTypedArrayCantComputeMask
    39. OutOfBounds
    40. GetElemStringNotCached
    41. NonNativeReceiver
    42. IndexType
    43. SetElemNonDenseNonTANotCached
    44. NoSimdJitSupport
    45. SimdTypeNotOptimized
    46. UnknownSimdProperty
    47. HasCommonInliningPath
    48. Inlined
    49. DOM
    50. Monomorphic
    51. Polymorphic
  2. Inline Cache Outcomes
    1. ICOptStub_GenericSuccess
    2. ICGetPropStub_ReadSlot
    3. ICGetPropStub_CallGetter
    4. ICGetPropStub_ArrayLength
    5. ICGetPropStub_UnboxedRead
    6. ICGetPropStub_UnboxedReadExpando
    7. ICGetPropStub_UnboxedArrayLength
    8. ICGetPropStub_TypedArrayLength
    9. ICGetPropStub_DOMProxyShadowed
    10. ICGetPropStub_DOMProxyUnshadowed
    11. ICGetPropStub_GenericProxy
    12. ICGetPropStub_ArgumentsLength
    13. ICSetPropStub_Slot
    14. ICSetPropStub_GenericProxy
    15. ICSetPropStub_DOMProxyShadowed
    16. ICSetPropStub_DOMProxyUnshadowed
    17. ICSetPropStub_CallSetter
    18. ICSetPropStub_AddSlot
    19. ICSetPropStub_SetUnboxed
    20. ICGetElemStub_ReadSlot
    21. ICGetElemStub_CallGetter
    22. ICGetElemStub_ReadUnboxed
    23. ICGetElemStub_Dense
    24. ICGetElemStub_DenseHole
    25. ICGetElemStub_TypedArray
    26. ICGetElemStub_ArgsElement
    27. ICGetElemStub_ArgsElementStrict
    28. ICSetElemStub_Dense
    29. ICSetElemStub_TypedArray
    30. ICNameStub_ReadSlot
    31. ICNameStub_CallGetter
  3. Call Inlining Outcomes
    1. CantInlineGeneric
    2. CantInlineClassConstructor
    3. CantInlineExceededDepth
    4. CantInlineExceededTotalBytecodeLength
    5. CantInlineBigCaller
    6. CantInlineBigCallee
    7. CantInlineBigCalleeInlinedBytecodeLength
    8. CantInlineNotHot
    9. CantInlineNotInDispatch
    10. CantInlineNativeBadType
    11. CantInlineNoTarget
    12. CantInlineNotInterpreted
    13. CantInlineNoBaseline
    14. CantInlineLazy
    15. CantInlineNotConstructor
    16. CantInlineDisableIon
    17. CantInlineTooManyArgs
    18. CantInlineRecursive
    19. CantInlineHeavyweight
    20. CantInlineNeedsArgsObj
    21. CantInlineDebuggee
    22. CantInlineUnknownProps
    23. CantInlineUnreachable
    24. CantInlineBound
    25. CantInlineNativeNoSpecialization
    26. CantInlineNativeBadForm
    27. CantInlineBadType
    28. CantInlineNativeNoTemplateObj

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SpiderMonkey's optimizing JIT, IonMonkey, uses different optimization strategies to speed up various operations. The most typical operations that are relevant for fast program execution are property accesses and function calls.

This page documents the meaning of different optimization outcomes.

General Outcomes

General outcomes shared between various optimization strategies.

GenericFailure

The optimization attempt failed, and the reason was not recorded.

GenericSuccess

Optimization succeeded.

Disabled

The optimization has been explicitly disallowed.

NoTypeInfo

Optimization failed because there was no type information associated with an object containing the property. This failure mode is unlikely and occurs if the target object is obtained in some roundabout way.

NoAnalysisInfo

TODO

NoShapeInfo

The baseline compiler recorded no usable shape information for this operation.

UnknownObject

The type of the object is not known. This can happen if the operation sees many different types of objects, and so the type of the input to the operation cannot be resolved to a single type.

UnknownProperties

Optimization failed because the object containing the property was marked as having unknown properties. This can happen if too many properties are defined on the object, or if delete is used to remove one of the object's properties.

Singleton

One of the types present in the typeset was a singleton type, preventing the optimization from being enabled.

NotSingleton

Optimization failed because the object containing the property did not have a 'singleton' type. Singleton types are assigned to objects that are "one of a kind", such as global objects, literal objects declared in the global scope, and top-level function objects.

NotFixedSlot

The property being accessed is not stored at a known location in the object. This can occur if one of the expected types of objects to be used in this operation has unknown properties, or if different instances of the object store the property at different locations (for example, some instances have the property assigned in a different order than others).

InconsistentFixedSlot

The property being accessed is not stored at a known location in the object. This can occur if the operation is polymorphic on different object types and one or more of the object types contain the property at a different slot than the others.

NotObject

Optimization failed because the stored in the property could potentially be a non-object value. Since only objects can be uniquely typed, the optimization strategy fails in this case.

NotStruct

The object holding the property is not a typed struct object.

NotUnboxed

The object whose property is being accessed is not formatted as an unboxed object.

UnboxedConvertedToNative

The object whose property is being accessed was previously unboxed but was deoptimized and converted to a native object.

StructNoField

The unboxed property being accessed does not correspond to a field on the typed object.

InconsistentFieldType

The type of an unboxed field is not consistent across all the different types of objects it could be accessed from.

InconsistentFieldOffset

The offset of an unboxed field is not consistent across all the different types of objects it could be accessed from.

NeedsTypeBarrier

Optimization failed because somehow the property was accessed in a way that returned a different type than the expected constant. This is an unlikely failure mode, and should not occur.

InDictionaryMode

The object whose property is being accessed is in dictionary mode. Objects which are used in ways that suggest they are hashtables are turned into dictionary objects and their types marked as such.

NoProtoFound

A prototype object was not found for all the object used by this operation.

MultiProtoPaths

Objects used in this operation had differing prototypes.

NonWritableProperty

The property being assigned to is not writable for some types of objects which are used in this operation.

ProtoIndexedProps

The object being accessed has indexed properties that are exotic (for example, defined as a property on a prototype object and left as a hole in the underlying object).

ArrayBadFlags

The array being accessed may have flags that the optimization strategy cannot handle. For example, if the array has sparse indexes, or has indexes that overflow the array's length, the optimization strategy may fail.

ArrayDoubleConversion

The type-system indicates that some arrays at this site should be converted to packed arrays of doubles while others should not. The optimization strategy fails for this condition.

ArrayRange

Could not accurately calculate the range attributes of an inline array creation.

ArraySeenNegativeIndex

Arrays at this element access location have seen negative indexes.

TypedObjectNeutered

The typed object being accessed at this location may have been neutered (a neutered typed object is one where the underlying byte buffer has been removed or transferred to a worker).

TypedObjectArrayRange

Failed to do range check of element access on a typed object.

AccessNotDense

AccessNotSimdObject

The observed type of the target of the property access doesn't guarantee that it is an SIMD object.

AccessNotTypedObject

The observed type of the target of the property access doesn't guarantee that it is a TypedObject.

AccessNotTypedArray

AccessNotString

StaticTypedArrayUint32

StaticTypedArrayCantComputeMask

OutOfBounds

GetElemStringNotCached

NonNativeReceiver

IndexType

SetElemNonDenseNonTANotCached

NoSimdJitSupport

Optimization failed because SIMD JIT support was not enabled.

SimdTypeNotOptimized

The type observed as being retrieved from this property access did not match an optimizable type.

UnknownSimdProperty

The property being accessed on the object is not one of the optimizable property names.

HasCommonInliningPath

Inlined

DOM

Monomorphic

Polymorphic

Inline Cache Outcomes

Outcomes describing inline cache stubs that were generated.

ICOptStub_GenericSuccess

ICGetPropStub_ReadSlot

ICGetPropStub_CallGetter

ICGetPropStub_ArrayLength

ICGetPropStub_UnboxedRead

ICGetPropStub_UnboxedReadExpando

ICGetPropStub_UnboxedArrayLength

ICGetPropStub_TypedArrayLength

ICGetPropStub_DOMProxyShadowed

ICGetPropStub_DOMProxyUnshadowed

ICGetPropStub_GenericProxy

ICGetPropStub_ArgumentsLength

ICSetPropStub_Slot

ICSetPropStub_GenericProxy

ICSetPropStub_DOMProxyShadowed

ICSetPropStub_DOMProxyUnshadowed

ICSetPropStub_CallSetter

ICSetPropStub_AddSlot

ICSetPropStub_SetUnboxed

ICGetElemStub_ReadSlot

ICGetElemStub_CallGetter

ICGetElemStub_ReadUnboxed

ICGetElemStub_Dense

ICGetElemStub_DenseHole

ICGetElemStub_TypedArray

ICGetElemStub_ArgsElement

ICGetElemStub_ArgsElementStrict

ICSetElemStub_Dense

ICSetElemStub_TypedArray

ICNameStub_ReadSlot

ICNameStub_CallGetter

Call Inlining Outcomes

Optimization outcomes of attempts to inline function calls.

CantInlineGeneric

CantInlineClassConstructor

CantInlineExceededDepth

CantInlineExceededTotalBytecodeLength

CantInlineBigCaller

CantInlineBigCallee

CantInlineBigCalleeInlinedBytecodeLength

CantInlineNotHot

CantInlineNotInDispatch

CantInlineNativeBadType

CantInlineNoTarget

Unable to inline function call. The callee (target) function, f in f(x), is not known at JIT time.

CantInlineNotInterpreted

Unable to inline function call. The callee function is not an interpreted function. For example, it could be a native function for which Ion has no built-in specialization.

CantInlineNoBaseline

Unable to inline function call. The interpreted callee function could not be compiled by the Baseline compiler.

CantInlineLazy

Unable to inline function call. The interpreted callee function has a lazy, compiled on-demand script instead of an already compiled script.

CantInlineNotConstructor

Unable to inline function call. Rare. The interpreted callee function is invoked with new but cannot be called as a constructor. Property accessors, Function.prototype, and arrow (=>) functions cannot be called as constructors.

CantInlineDisableIon

Unable to inline function call. The interpreted callee function has been explicitly blacklisted against Ion compilation.

CantInlineTooManyArgs

Unable to inline function call. The interpreted callee function either has too many parameters or is called with too many arguments. These thresholds are subject to change.

CantInlineRecursive

Unable to inline function call. The interpreted callee function recurs for more than one level. The first level of recursion is inlinable.

CantInlineHeavyweight

Unable to inline function call. The interpreted callee function contains variables bindings that are closed over. For example, function f() { var x; return function () { x++; } } closes over x in f.

CantInlineNeedsArgsObj

Unable to inline function call. The interpreted callee function requires an arguments object to be created.

CantInlineDebuggee

Unable to inline function call. The interpreted callee function is being debugged by the Debugger API.

CantInlineUnknownProps

Unable to inline function call. The engine knows nothing definite about the type of the callee function object.

CantInlineUnreachable

Unable to inline function call. The call site has not been observed to have ever been executed. It lacks observed type information for its arguments, its return value, or both.

CantInlineBound

Unable to inline function call. The interpreted callee is a bound function generated from Function.prototype.bind that failed some sub-checks. (expand)

CantInlineNativeNoSpecialization

Unable to inline function call. Ion does not have built-in specialization for the native (implemented in C++) callee function.

CantInlineNativeBadForm

Unable to inline function call. The native callee function was called with an unsupported number of arguments, or calling non-constructing functions with new.

CantInlineBadType

Unable to inline function call. The native callee function was called with arguments with types that the built-in specialization does not support. For example, calling Math functions on objects.

CantInlineNativeNoTemplateObj

Unable to inline function call. Cannot inline a native constructor (e.g., new Array) because no template object was cached by the Baseline compiler. (expand)

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 Contributors to this page: rolfedh, kvijayan
 Last updated by: rolfedh,