dotty.tools.backend.jvm

This trait contains code shared between GenBCode and GenASM that depends on types defined in the compiler cake (Global).

The BTypes component defines The BType class hierarchy. BTypes encapsulates all type information that is required after building the ASM nodes. This includes optimizations, geneartion of InnerClass attributes and generation of stack map frames.

This representation is immutable and independent of the compiler data structures, hence it can be queried by concurrent threads.

This class mainly contains the method classBTypeFromSymbol, which extracts the necessary information from a symbol and its type to create the corresponding ClassBType. It requires access to the compiler (global parameter).

The mixin CoreBTypes defines core BTypes that are used in the backend. Building these BTypes uses classBTypeFromSymbol, hence requires access to the compiler (global).

BTypesFromSymbols extends BTypes because the implementation of BTypes requires access to some of the core btypes. They are declared in BTypes as abstract members. Note that BTypes does not have access to the compiler instance.

For the last mile: turning generated bytecode in memory into something you can use. Has implementations for writing to class files, jars, and disassembled/javap output.

Collect all super calls to trait members.

For each super reference to trait member, register a call from the current class to the owner of the referenced member.

This information is used to know if it is safe to remove a redundant mixin class. A redundant mixin class is one that is implemented by another mixin class. As the methods in a redundant mixin class could be implemented with a default abstract method, the redundant mixin class could be required as a parent by the JVM.

Core BTypes and some other definitions. The initialization of these definitions requies access to symbols / types (global).

The symbols used to initialize the ClassBTypes may change from one compiler run to the next. To make sure the definitions are consistent with the symbols in the current run, the intializeCoreBTypes method in BTypesFromSymbols creates a new instance of CoreBTypes in each compiler run.

The class BTypesFromSymbols does not directly reference CoreBTypes, but CoreBTypesProxy. The reason is that having a var bTypes: CoreBTypes would not allow import bTypes._. Instead, the proxy class holds a CoreBTypes in a variable field and forwards to this instance.

The definitions in CoreBTypes need to be lazy vals to break an initialization cycle. When creating a new instance to assign to the proxy, the classBTypeFromSymbol invoked in the constructor will actucally go through the proxy. The lazy vals make sure the instance is assigned in the proxy before the fields are initialized.

Note: if we did not re-create the core BTypes on each compiler run, BType.classBTypeFromInternalNameMap could not be a perRunCache anymore: the classes defeined here need to be in that map, they are added when the ClassBTypes are created. The per run cache removes them, so they would be missing in the second run.

See comment in class CoreBTypes.

This trait make some core BTypes availalbe that don't depend on a Global instance. Some core BTypes are required to be accessible in the BTypes trait, which does not have access to Global.

BTypes cannot refer to CoreBTypesProxy because some of its members depend on global, for example the type Symbol in def primitiveTypeMap: Map[Symbol, PrimitiveBType]

Scala primitive operations are represented as methods in Any and AnyVal subclasses. Here we demultiplex them by providing a mapping from their symbols to integers. Different methods exist for different value types, but with the same meaning (like plus, minus, etc.). They will all be mapped to the same int.

Note: The three equal methods have the following semantics:

• "==" checks for null, and if non-null, calls java.lang.Object.equals (class: Any; modifier: final). Primitive: EQ
• "eq" usual reference comparison (class: AnyRef; modifier: final). Primitive: ID
• "equals" user-defined equality (Java semantics) (class: Object; modifier: none). Primitive: EQUALS

Inspired from the scalac compiler.

Can't output a file due to the state of the file system.