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[DOC] Update compiler phases in documentation #6971

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Jul 31, 2019
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[DOC] Update compiler phases in documentation #6971

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31 changes: 21 additions & 10 deletions docs/docs/internals/overall-structure.md
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Original file line number Diff line number Diff line change
Expand Up @@ -91,15 +91,18 @@ Seen from a temporal perspective, the `dotc` compiler consists of a list of
phases. The current list of phases is specified in class [Compiler] as follows:

```scala
def phases: List[List[Phase]] =
def phases: List[List[Phase]] =
frontendPhases ::: picklerPhases ::: transformPhases ::: backendPhases

/** Phases dealing with the frontend up to trees ready for TASTY pickling */
protected def frontendPhases: List[List[Phase]] =
List(new FrontEnd) :: // Compiler frontend: scanner, parser, namer, typer
List(new YCheckPositions) :: // YCheck positions
List(new Staging) :: // Check PCP, heal quoted types and expand macros
List(new sbt.ExtractDependencies) :: // Sends information on classes' dependencies to sbt via callbacks
List(new PostTyper) :: // Additional checks and cleanups after type checking
List(new sbt.ExtractAPI) :: // Sends a representation of the API of classes to sbt via callbacks
List(new SetRootTree) :: // Set the `rootTreeOrProvider` on class symbols
Nil

/** Phases dealing with TASTY tree pickling and unpickling */
Expand All @@ -113,25 +116,26 @@ phases. The current list of phases is specified in class [Compiler] as follows:
List(new FirstTransform, // Some transformations to put trees into a canonical form
new CheckReentrant, // Internal use only: Check that compiled program has no data races involving global vars
new ElimPackagePrefixes, // Eliminate references to package prefixes in Select nodes
new CookComments) :: // Cook the comments: expand variables, doc, etc.
new CookComments, // Cook the comments: expand variables, doc, etc.
new CompleteJavaEnums) :: // Fill in constructors for Java enums
List(new CheckStatic, // Check restrictions that apply to @static members
new ElimRepeated, // Rewrite vararg parameters and arguments
new ExpandSAMs, // Expand single abstract method closures to anonymous classes
new ProtectedAccessors, // Add accessors for protected members
new ExtensionMethods, // Expand methods of value classes with extension methods
new CacheAliasImplicits, // Cache RHS of parameterless alias implicits
new ShortcutImplicits, // Allow implicit functions without creating closures
new ByNameClosures, // Expand arguments to by-name parameters to closures
new LiftTry, // Put try expressions that might execute on non-empty stacks into their own methods
new HoistSuperArgs, // Hoist complex arguments of supercalls to enclosing scope
new ClassOf, // Expand `Predef.classOf` calls.
new RefChecks) :: // Various checks mostly related to abstract members and overriding
List(new TryCatchPatterns, // Compile cases in try/catch
List(new ElimOpaque, // Turn opaque into normal aliases
new TryCatchPatterns, // Compile cases in try/catch
new PatternMatcher, // Compile pattern matches
new ExplicitOuter, // Add accessors to outer classes from nested ones.
new ExplicitSelf, // Make references to non-trivial self types explicit as casts
new StringInterpolatorOpt, // Optimizes raw and s string interpolators by rewriting them to string concatentations
new CrossCastAnd, // Normalize selections involving intersection types.
new Splitter) :: // Expand selections involving union types into conditionals
new CrossCastAnd) :: // Normalize selections involving intersection types.
List(new PruneErasedDefs, // Drop erased definitions from scopes and simplify erased expressions
new VCInlineMethods, // Inlines calls to value class methods
new SeqLiterals, // Express vararg arguments as arrays
Expand All @@ -140,13 +144,16 @@ phases. The current list of phases is specified in class [Compiler] as follows:
new ElimByName, // Expand by-name parameter references
new CollectNullableFields, // Collect fields that can be nulled out after use in lazy initialization
new ElimOuterSelect, // Expand outer selections
new AugmentScala2Traits, // Expand traits defined in Scala 2.x to simulate old-style rewritings
new ResolveSuper, // Implement super accessors and add forwarders to trait methods
new AugmentScala2Traits, // Augments Scala2 traits with additional members needed for mixin composition.
new ResolveSuper, // Implement super accessors
new FunctionXXLForwarders, // Add forwarders for FunctionXXL apply method
new TupleOptimizations, // Optimize generic operations on tuples
new ArrayConstructors) :: // Intercept creation of (non-generic) arrays and intrinsify.
List(new Erasure) :: // Rewrite types to JVM model, erasing all type parameters, abstract types and refinements.
List(new ElimErasedValueType, // Expand erased value types to their underlying implmementation types
new VCElideAllocations, // Peep-hole optimization to eliminate unnecessary value class allocations
new ArrayApply, // Optimize `scala.Array.apply([....])` and `scala.Array.apply(..., [....])` into `[...]`
new ElimPolyFunction, // Rewrite PolyFunction subclasses to FunctionN subclasses
new TailRec, // Rewrite tail recursion to loops
new Mixin, // Expand trait fields and trait initializers
new LazyVals, // Expand lazy vals
Expand All @@ -156,8 +163,10 @@ phases. The current list of phases is specified in class [Compiler] as follows:
List(new Constructors, // Collect initialization code in primary constructors
// Note: constructors changes decls in transformTemplate, no InfoTransformers should be added after it
new FunctionalInterfaces, // Rewrites closures to implement @specialized types of Functions.
new GetClass) :: // Rewrites getClass calls on primitive types.
List(new LinkScala2Impls, // Redirect calls to trait methods defined by Scala 2.x, so that they now go to their implementations
new Instrumentation, // Count closure allocations under -Yinstrument-closures
new GetClass, // Rewrites getClass calls on primitive types.
new LiftTry) :: // Put try expressions that might execute on non-empty stacks into their own methods their implementations
List(new LinkScala2Impls, // Redirect calls to trait methods defined by Scala 2.x, so that they now go to
new LambdaLift, // Lifts out nested functions to class scope, storing free variables in environments
// Note: in this mini-phase block scopes are incorrect. No phases that rely on scopes should be here
new ElimStaticThis) :: // Replace `this` references to static objects by global identifiers
Expand All @@ -168,12 +177,14 @@ phases. The current list of phases is specified in class [Compiler] as follows:
new ExpandPrivate, // Widen private definitions accessed from nested classes
new RestoreScopes, // Repair scopes rendered invalid by moving definitions in prior phases of the group
new SelectStatic, // get rid of selects that would be compiled into GetStatic
new sjs.JUnitBootstrappers, // Generate JUnit-specific bootstrapper classes for Scala.js (not enabled by default)
new CollectEntryPoints, // Find classes with main methods
new CollectSuperCalls) :: // Find classes that are called with super
Nil

/** Generate the output of the compilation */
protected def backendPhases: List[List[Phase]] =
List(new sjs.GenSJSIR) :: // Generate .sjsir files for Scala.js (not enabled by default)
List(new GenBCode) :: // Generate JVM bytecode
Nil
```
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