public abstract class ConditionProfile extends Profile
ConditionProfiles are useful to profile the outcome of conditions.
Usage example:
class AbsoluteNode extends Node { final ConditionProfile greaterZeroProfile = ConditionProfile.create{Binary,Counting}Profile(); void execute(int value) { if (greaterZeroProfile.profile(value >= 0)) { return value; } else { return -value; } } }
A profile is a Truffle utility class that uses the Truffle compiler
directives
to guard for and/or forward runtime information to the compiler.
Usage: Profiles should be stored in final
or compilation final
fields of node classes to ensure that they can get optimized properly.
Profiles must not be shared between ASTs. Using the same profile multiple times in a single
node
or in multiple nodes
which link
to the
same root
is allowed. Never store profiles inside runtime values that
leave the scope of the originating AST. This limitation exists because the used mechanism to
invalidate compiled code performs local invalidations only. For global speculations use
assumptions
instead.
Compilation: Some profiles like branch
profiles do not induce
additional overhead in compiled code. Others like value
profiles might
require a runtime check to verify their assumptions which are forwarded to the compiler. Even if
profiles do not induce direct overhead in compiled code it still might get invalidated as a
result of using profiles. Invalidating profiles will result in the invalidation of compiled code.
It is therefore essential to place these profiles in way that is neither too aggressive nor too
conservative.
Footprint: Whether profiling information can be forwarded to the compiler depends on the
capabilities of the runtime system
. If the runtime returns
true
in TruffleRuntime.isProfilingEnabled()
then runtime information will
get collected. This comes at at the cost of additional overhead and footprint in interpreted
mode. Thats why the factory methods of profiles can return implementations where profiling is
disabled. Using disabled profiles makes sense for runtimes that are unable to use the collected
profiling information. Even runtime implementations that are able to use this information might
decide to turn off profiling for benchmarking purposes.
Profile subclasses:
BranchProfile
to profile on unlikely branches like errors.ConditionProfile
to profile on conditionals or boolean values.LoopConditionProfile
to profile on conditionals of loops with special support for
counted loops.ValueProfile
to profile on properties like type and identity of values.ByteValueProfile
to profile on byte
values.IntValueProfile
to profile on int
values.LongValueProfile
to profile on long
values.FloatValueProfile
to profile on float
values.DoubleValueProfile
to profile on double
values.PrimitiveValueProfile
to profile on objects by identity and on primitives by value.
ConditionProfile.createBinaryProfile()
,
ConditionProfile.createCountingProfile()
,
LoopConditionProfile
Modifier and Type | Method and Description |
---|---|
static ConditionProfile |
create()
Creates a binary ConditionProfile using
ConditionProfile.createBinaryProfile() . |
static ConditionProfile |
createBinaryProfile()
|
static ConditionProfile |
createCountingProfile()
|
static ConditionProfile |
getUncached()
Returns the uncached version of the profile.
|
abstract boolean |
profile(boolean value) |
clone
public abstract boolean profile(boolean value)
public static ConditionProfile createCountingProfile()
ConditionProfile
that speculates on conditions to be never
true
or to be never false
. Additionally to a binary profile this
method returns a condition profile that also counts the number of times the condition was
true and false. This information is reported to the underlying optimization system using
CompilerDirectives.injectBranchProbability(double, boolean)
. Condition profiles are
intended to be used as part of if conditions.ConditionProfile
,
ConditionProfile.createBinaryProfile()
public static ConditionProfile createBinaryProfile()
ConditionProfile
that speculates on conditions to be never
true
or to be never false
. Condition profiles are intended to be
used as part of if conditions.ConditionProfile
,
ConditionProfile.createCountingProfile()
public static ConditionProfile create()
ConditionProfile.createBinaryProfile()
. This is a convenience
method so it can be used as @Cached ConditionProfile myProfile
instead of the much
longer @Cached("createBinaryProfile()") ConditionProfile myProfile
.public static ConditionProfile getUncached()