js/src/doc/JITOptimizations/Outcomes.md
author Kannan Vijayan <kvijayan@mozilla.com>
Tue, 04 Aug 2015 09:58:00 -0400
changeset 287823 b06bebbf0ed771a98924cfb3656ef3fc228c1b7e
child 293540 429b04491fe19a231d60b3b8cda2b6d5754d2767
permissions -rw-r--r--
Bug 1145442 - Add documentation for JIT strategies. r=shu

# JIT Optimization Outcomes

SpiderMonkey's optimizing JIT, IonMonkey, uses a number of different
optimization strategies to speed up various operations. The most commonplace
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

### NoTypeInfo

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

### NoAnalysisInfo
### NoShapeInfo
### UnknownObject
### UnknownProperties

### 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
### NotSingleton

### 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
### InconsistentFixedSlot

### 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
### UnboxedConvertedToNative

### StructNoField

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

### InconsistentFieldType
### InconsistentFieldOffset

### 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
### NoProtoFound
### MultiProtoPaths
### NonWritableProperty
### ProtoIndexedProps
### ArrayBadFlags
### ArrayDoubleConversion
### ArrayRange
### ArraySeenNegativeIndex
### TypedObjectNeutered
### TypedObjectArrayRange
### AccessNotDense

### AccessNotSimdObject

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

### 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)