dotty.tools.backend.jvm.opt
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Type members
Classlikes
Information about invocation arguments, obtained through data flow analysis of the callsite method.
Information about invocation arguments, obtained through data flow analysis of the callsite method.
Attributes
- Supertypes
- Known subtypes
The BCodeRepository provides utilities to read the bytecode of classfiles from the compilation classpath. Parsed classes are cached in the classes map.
The BCodeRepository provides utilities to read the bytecode of classfiles from the compilation classpath. Parsed classes are cached in the classes map.
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A callee in the call graph.
A callee in the call graph.
Value parameters
- annotatedInline
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True if the callee is annotated @inline
- annotatedNoInline
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True if the callee is annotated @noinline
- callee
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The callee, as it appears in the invocation instruction. For virtual calls, an override of the callee might be invoked. Also, the callee can be abstract.
- calleeDeclarationClass
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The class in which the callee is declared
- calleeInfoWarning
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An inliner warning if some information was not available while gathering the information about this callee.
- isStaticallyResolved
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True if the callee cannot be overridden
- samParamTypes
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A map from parameter positions to SAM parameter types
Attributes
- Supertypes
Used in the CallGraph for nodes where an issue occurred determining the callee information.
Used in the CallGraph for nodes where an issue occurred determining the callee information.
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- Known subtypes
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trait Serializabletrait Producttrait Equalstrait CannotInlineWarningtrait OptimizerWarningclass Objecttrait Matchableclass AnyShow all
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class KnownCallsiteclass UnknownCallsite
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class CalleeNotFinalclass IllegalAccessCheckFailedclass NoBytecodeclass ResultingMethodTooLargeclass StrictfpMismatchclass SynchronizedMethodShow all
Used in the InlineInfo of a ClassBType, when some issue occurred obtaining the inline information.
Used in the InlineInfo of a ClassBType, when some issue occurred obtaining the inline information.
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trait Serializabletrait Producttrait Equalstrait MissingBytecodeWarningtrait OptimizerWarningclass Objecttrait Matchableclass AnyShow all
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trait Serializabletrait Producttrait Equalstrait ClassInlineInfoWarningtrait OptimizerWarningclass Objecttrait Matchableclass AnyShow all
Metadata about a closure instantiation, stored in the call graph
Metadata about a closure instantiation, stored in the call graph
Value parameters
- capturedArgInfos
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information about captured arguments. Used for updating the call graph when re-writing a closure invocation to the body method.
- lambdaMetaFactoryCall
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the InvokeDynamic instruction
- ownerClass
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the class containing the above method
- ownerMethod
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the method where the closure is allocated
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- Companion
- class
- Supertypes
- Self type
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ClosureOptimizer.type
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trait Serializabletrait Producttrait Equalstrait MissingBytecodeWarningtrait OptimizerWarningclass Objecttrait Matchableclass AnyShow all
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trait Serializabletrait Producttrait Equalstrait ArgInfoclass Objecttrait Matchableclass AnyShow all
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FunctionLiteral.type
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trait Serializabletrait Producttrait Equalstrait CannotInlineWarningtrait OptimizerWarningclass Objecttrait Matchableclass AnyShow all
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trait Serializabletrait Producttrait Equalstrait CannotInlineWarningtrait OptimizerWarningclass Objecttrait Matchableclass AnyShow all
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- class
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InlineInfo.type
Metadata about a ClassBType, used by the inliner.
Metadata about a ClassBType, used by the inliner.
More information may be added in the future to enable more elaborate inline heuristics. Note that this class should contain information that can only be obtained from the ClassSymbol. Information that can be computed from the ClassNode should be added to the call graph instead.
Value parameters
- isAccessible
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Whether this class's internals can be inlined into callsites, i.e., it is exported from a public module.
- isEffectivelyFinal
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True if the class cannot have subclasses: final classes, module classes.
- methodInfos
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The MethodInlineInfos for the methods declared in this class. The map is indexed by the string s"$name$descriptor" (to disambiguate overloads).
- sam
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If this class is a SAM type, the SAM's "$name$descriptor".
- warning
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Contains a warning message if an error occurred when building this InlineInfo, for example if some classfile could not be found on the classpath. This warning can be reported later by the inliner.
Attributes
- Companion
- object
- Supertypes
This attribute stores the InlineInfo for a ClassBType as an independent classfile attribute. The compiler does so for every class being compiled.
This attribute stores the InlineInfo for a ClassBType as an independent classfile attribute. The compiler does so for every class being compiled.
The reason is that a precise InlineInfo can only be obtained if the symbol for a class is available. For example, we need to know if a method is final in Scala's terms, or if it has the @inline annotation. Looking up a class symbol for a given class filename is brittle (name-mangling).
The attribute is also helpful for inlining mixin methods. The mixin phase only adds mixin method symbols to classes that are being compiled. For all other class symbols, there are no mixin members. However, the inliner requires an InlineInfo for inlining mixin members. That problem is solved by reading the InlineInfo from this attribute.
In principle, we could encode the InlineInfo into a Java annotation (instead of a classfile attribute). However, an attribute allows us to save many bits. In particular, note that the strings in an InlineInfo are serialized as references to constants in the constant pool, and those strings (method names, method signatures) would exist in there anyway. So the ScalaInlineAttribute remains relatively compact.
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trait Serializabletrait Producttrait Equalsclass Attributeclass Objecttrait Matchableclass AnyShow all
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object InlineInfoAttributePrototype
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InlineInfoAttribute.type
In order to instruct the ASM framework to deserialize the ScalaInlineInfo attribute, we need to pass a prototype instance when running the class reader.
In order to instruct the ASM framework to deserialize the ScalaInlineInfo attribute, we need to pass a prototype instance when running the class reader.
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class InlineInfoAttributetrait Serializabletrait Producttrait Equalsclass Attributeclass Objecttrait Matchableclass AnyShow all
- Self type
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- class
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InlinerHeuristics.type
A callsite in the call graph.
A callsite in the call graph.
Value parameters
- argInfos
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Information about the invocation receiver and arguments
- callee
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The callee, as it appears in the invocation instruction. For virtual calls, an override of the callee might be invoked. Also, the callee can be abstract. Contains a warning message if the callee MethodNode cannot be found in the bytecode repository.
- callsiteClass
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The class containing the callsite
- callsiteInstruction
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The invocation instruction
- callsiteMethod
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The method containing the callsite
- callsitePosition
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The source position of the callsite, used for inliner warnings.
- callsiteStackHeight
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The stack height at the callsite, required by the inliner
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trait Serializabletrait Producttrait Equalstrait Callsiteclass Objecttrait Matchableclass AnyShow all
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trait Serializabletrait Producttrait Equalstrait RemovePairDependencyclass Objecttrait Matchableclass AnyShow all
Optimizations within a single method. Certain optimizations enable others, for example removing unreachable code can render a try block empty and enable removeEmptyExceptionHandlers. The latter in turn enables more unreachable code to be eliminated (the catch block), so there is a cyclic dependency. Optimizations that depend on each other are therefore executed in a loop until reaching a fixpoint.
Optimizations within a single method. Certain optimizations enable others, for example removing unreachable code can render a try block empty and enable removeEmptyExceptionHandlers. The latter in turn enables more unreachable code to be eliminated (the catch block), so there is a cyclic dependency. Optimizations that depend on each other are therefore executed in a loop until reaching a fixpoint.
The optimizations marked UPSTREAM enable optimizations that were already executed, so they cause another iteration in the fixpoint loop.
nullness optimizations: rewrite null-checking branches to GOTO if nullness is known
- enables downstream
- unreachable code (null / non-null branch becomes unreachable)
- box-unbox elimination (may render an escaping consumer of a box unreachable)
- stale stores (aload x is replaced by aconst_null if it's known null)
- simplify jumps (replaces conditional jumps by goto, so may enable goto chains)
unreachable code / DCE (removes instructions of basic blocks to which there is no branch)
- enables downstream:
- stale stores (loads may be eliminated, removing consumers of a store)
- empty handlers (try blocks may become empty)
- simplify jumps (goto l; [dead code]; l: ...) => remove goto
- stale local variable descriptors
- (not box-unbox, which is implemented using prod-cons, so it doesn't consider dead code)
note that eliminating empty handlers and stale local variable descriptors is required for correctness, see the comment in the body of methodOptimizations.
box-unbox elimination (eliminates box-unbox pairs within the same method)
- enables UPSTREAM:
- nullness optimizations (a box extraction operation (unknown nullness) may be rewritten to a read of a non-null local. example in doc comment of box-unbox implementation)
- further box-unbox elimination (e.g. an Integer stored in a Tuple; eliminating the tuple may enable eliminating the Integer)
- enables downstream:
- copy propagation (new locals are introduced, may be aliases of existing)
- stale stores (multi-value boxes where not all values are used)
- redundant casts (
("a", "b")._1: the generic_1method returnsObject, a cast to String is added. The cast is redundant after eliminating the tuple.) - empty local variable descriptors (local variables that were holding the box may become unused)
- push-pop (due to artifacts of eliminating runtime type tests on primitives)
copy propagation (replaces LOAD n to the LOAD m for the smallest m that is an alias of n)
- enables downstream:
- stale stores (a stored value may not be loaded anymore)
- store-load pairs (a load n may now be right after a store n)
stale stores (replace STORE by POP), rewrites ClassTag(x).newArray, inlines array_apply/update
- enables UPSTREAM:
- nullness optimizations (newArray rewrite or inlining may turn things non-null)
- enables downstream:
- push-pop (the new pop may be the single consumer for an instruction)
- redundant casts (because rewrites
newArray, the array type gets more precise)
redundant casts and rewrite some intrinsics: eliminates casts that are statically known to succeed (uses type propagation), rewrites instanceof checks, rewrites intrinsics.
- enables UPSTREAM:
- box-unbox elimination (a removed checkcast may be a box consumer)
- copy propagation (a removed checkcast may turn an upcasted local variable into an alias)
- enables downstream:
- push-pop for closure allocation elimination (every indyLambda is followed by a checkcast, see scala/bug#9540)
- redundant casts (changing an instanceof to true/false removes branches and can make types of other values more precise)
push-pop (when a POP is the only consumer of a value, remove the POP and its producer)
- enables UPSTREAM:
- stale stores (if a LOAD is removed, a corresponding STORE may become stale)
- box-unbox elimination (push-pop may eliminate a closure allocation, rendering a captured box non-escaping)
- redundant casts (Int.unbox(x) is replaced by
x.asInstanceOf[Integer]; pop) - nullness (
x.intValueis replaced byif (x == null) throw null)
- enables downstream:
- store-load pairs (a variable may become non-live)
- stale handlers (push-pop removes code)
- simplify jumps (push-pop removes code)
store-load pairs (remove STORE x; LOAD x if x is otherwise not used in the method)
- enables downstream:
- empty handlers (code is removes, a try block may become empty)
- simplify jumps (code is removed, a goto may become redundant for example)
- stale local variable descriptors
empty handlers (removes exception handlers whose try block is empty)
- enables UPSTREAM:
- unreachable code (catch block becomes unreachable)
- box-unbox (a box may be escape in an operation in a dead handler)
- enables downstream:
- simplify jumps
simplify jumps (various, like GOTO l; l: ..., see doc comments of individual optimizations)
- enables UPSTREAM
- unreachable code (
GOTO a; a: GOTO b; b: ..., the first jump is changed toGOTO b, the second becomes unreachable) - store-load pairs (a
GOTO l; l: ...is removed between store and load) - push-pop (
IFNULL l; l: ...is replaced byPOP)
- unreachable code (
The following cleanup optimizations don't enable any upstream optimizations, so they can be executed once at the end, when the above optimizations reach a fixpoint.
empty local variable descriptors (removes unused variables from the local variable table)
empty line numbers (eliminates line number nodes that describe no executable instructions)
At this point, we used to filter out redundant label nodes (sequences of labels without any executable instructions in between). However, this operation is relatively expensive, and unnecessary: labels don't exist in the classfile, they are lowered to bytecode offsets, so redundant labels disappear by design.
Note on a method's maxLocals / maxStack: the backend only uses those values for running Analyzers. The values can be conservative approximations: if an optimization removes code and the maximal stack size is now smaller, the larger maxStack value will still work fine for running an Analyzer (just that frames allocate more space than required). The correct max values written to the bytecode are re-computed during classfile serialization. To keep things simpler, we don't update the max values in every optimization:
- we do it in
removeUnreachableCodeImpl, because it's quite straightforward - maxLocals is updated in
compactLocalVariables, which runs at the end of method optimizations
Note on updating the call graph: whenever an optimization eliminates a callsite or a closure instantiation, we eliminate the corresponding entry from the call graph.
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LocalOptImpls.type
Metadata about a method, used by the inliner.
Metadata about a method, used by the inliner.
Value parameters
- annotatedInline
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True if the method is annotated
@inline - annotatedNoInline
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True if the method is annotated
@noinline - effectivelyFinal
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True if the method cannot be overridden (in Scala)
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trait Serializabletrait Producttrait Equalstrait CalleeInfoWarningtrait OptimizerWarningclass Objecttrait Matchableclass AnyShow all
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trait Serializabletrait Producttrait Equalstrait CalleeInfoWarningtrait OptimizerWarningclass Objecttrait Matchableclass AnyShow all
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trait Serializabletrait Producttrait Equalstrait CalleeInfoWarningtrait OptimizerWarningclass Objecttrait Matchableclass AnyShow all
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trait Serializabletrait Producttrait Equalstrait MissingBytecodeWarningtrait OptimizerWarningclass Objecttrait Matchableclass AnyShow all
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trait Serializabletrait Producttrait Equalstrait CannotInlineWarningtrait OptimizerWarningclass Objecttrait Matchableclass AnyShow all
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- Known subtypes
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trait Serializabletrait Producttrait Equalstrait CannotInlineWarningtrait OptimizerWarningclass Objecttrait Matchableclass AnyShow all
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trait Serializabletrait Producttrait Equalstrait OptimizerWarningclass Objecttrait Matchableclass AnyShow all
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trait Serializabletrait Producttrait Equalstrait ClassInlineInfoWarningtrait OptimizerWarningclass Objecttrait Matchableclass AnyShow all
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OptimizerWarning.type
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trait CalleeInfoWarningclass MethodInlineInfoErrorclass MethodInlineInfoMissingtrait CannotInlineWarningclass CalleeNotFinalclass IllegalAccessCheckFailedclass NoBytecodeclass ResultingMethodTooLargeclass StrictfpMismatchclass SynchronizedMethodtrait ClassInlineInfoWarningclass NoInlineInfoAttributetrait MissingBytecodeWarningclass ClassNotFoundclass FieldNotFoundclass MethodNotFoundclass NoClassBTypeInfoShow all
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trait Serializabletrait Producttrait Equalstrait RemovePairDependencyclass Objecttrait Matchableclass AnyShow all
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class LabelNotLiveclass RemovePair
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trait Serializabletrait Producttrait Equalstrait CannotInlineWarningtrait OptimizerWarningclass Objecttrait Matchableclass AnyShow all
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trait Serializabletrait Producttrait Equalstrait OptimizerWarningclass Objecttrait Matchableclass AnyShow all
Used in rewriteClosureApplyInvocations when a closure apply callsite cannot be rewritten to the closure body method.
Used in rewriteClosureApplyInvocations when a closure apply callsite cannot be rewritten to the closure body method.
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trait Serializabletrait Producttrait Equalstrait OptimizerWarningclass Objecttrait Matchableclass AnyShow all
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StaticallyKnownArray.type
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trait Serializabletrait Producttrait Equalstrait CannotInlineWarningtrait OptimizerWarningclass Objecttrait Matchableclass AnyShow all
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trait Serializabletrait Producttrait Equalstrait CannotInlineWarningtrait OptimizerWarningclass Objecttrait Matchableclass AnyShow all
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trait Serializabletrait Producttrait Equalstrait Callsiteclass Objecttrait Matchableclass AnyShow all
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trait Singletontrait Producttrait Mirrortrait Serializabletrait Producttrait Equalstrait OptimizerWarningclass Objecttrait Matchableclass AnyShow all
- Self type
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trait Serializabletrait Producttrait Equalstrait ClassInlineInfoWarningtrait OptimizerWarningclass Objecttrait Matchableclass AnyShow all
Ordering for inline requests. Required to make the inliner deterministic:
Ordering for inline requests. Required to make the inliner deterministic:
- Always remove the same request when breaking inlining cycles
- Perform inlinings in a consistent order
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trait Ordering[KnownCallsite]trait PartialOrdering[KnownCallsite]trait Equiv[KnownCallsite]trait Serializabletrait Comparator[KnownCallsite]class Objecttrait Matchableclass AnyShow all
- Self type
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callsiteOrdering.type