diff options
Diffstat (limited to 'compiler/src/dotty/tools/dotc/transform/ShortcutImplicits.scala')
-rw-r--r-- | compiler/src/dotty/tools/dotc/transform/ShortcutImplicits.scala | 165 |
1 files changed, 165 insertions, 0 deletions
diff --git a/compiler/src/dotty/tools/dotc/transform/ShortcutImplicits.scala b/compiler/src/dotty/tools/dotc/transform/ShortcutImplicits.scala new file mode 100644 index 000000000..b5469610f --- /dev/null +++ b/compiler/src/dotty/tools/dotc/transform/ShortcutImplicits.scala @@ -0,0 +1,165 @@ +package dotty.tools.dotc +package transform + +import TreeTransforms._ +import core.DenotTransformers.IdentityDenotTransformer +import core.Symbols._ +import core.Contexts._ +import core.Types._ +import core.Flags._ +import core.Decorators._ +import core.StdNames.nme +import core.Names._ +import core.NameOps._ +import ast.Trees._ +import ast.tpd +import collection.mutable + +/** This phase optimizes code using implicit function types, by applying two rewrite rules. + * Let IF be the implicit function type + * + * implicit Us => R + * + * (1) A method definition + * + * def m(xs: Ts): IF = implicit (ys: Us) => E + * + * is expanded to two methods: + * + * def m(xs: Ts): IF = implicit (ys: Us) => m$direct(xs)(ys) + * def m$direct(xs: Ts)(ys: Us): R = E + * + * (and equivalently for methods with type parameters or a different number of value parameter lists). + * An abstract method definition + * + * def m(xs: Ts): IF + * + * is expanded to: + * + * def m(xs: Ts): IF + * def m$direct(xs: Ts)(ys: Us): R + * + * (2) A reference `qual.apply` where `qual` has implicit function type and + * `qual` refers to a method `m` is rewritten to a reference to `m$direct`, + * keeping the same type and value arguments as they are found in `qual`. + */ +class ShortcutImplicits extends MiniPhase with IdentityDenotTransformer { thisTransform => + import tpd._ + + override def phaseName: String = "shortcutImplicits" + val treeTransform = new Transform + + /** If this option is true, we don't specialize symbols that are known to be only + * targets of monomorphic calls. + * The reason for this option is that benchmarks show that on the JVM for monomorphic dispatch + * scenarios inlining and escape analysis can often remove all calling overhead, so we might as + * well not duplicate the code. We need more experience to decide on the best setting of this option. + */ + final val specializeMonoTargets = true + + class Transform extends TreeTransform { + def phase = thisTransform + + override def prepareForUnit(tree: Tree)(implicit ctx: Context) = new Transform + + /** A map to cache mapping local methods to their direct counterparts. + * A fresh map is created for each unit. + */ + private val directMeth = new mutable.HashMap[Symbol, Symbol] + + /** Should `sym` get a ..$direct companion? + * This is the case if (1) `sym` is a method with an implicit function type as final result type. + * However if `specializeMonoTargets` is false, we exclude symbols that are known + * to be only targets of monomorphic calls because they are effectively + * final and don't override anything. + */ + private def shouldBeSpecialized(sym: Symbol)(implicit ctx: Context) = + sym.is(Method, butNot = Accessor) && + defn.isImplicitFunctionType(sym.info.finalResultType) && + (specializeMonoTargets || !sym.isEffectivelyFinal || sym.allOverriddenSymbols.nonEmpty) + + /** @pre The type's final result type is an implicit function type `implicit Ts => R`. + * @return The type of the `apply` member of `implicit Ts => R`. + */ + private def directInfo(info: Type)(implicit ctx: Context): Type = info match { + case info: PolyType => info.derivedPolyType(resType = directInfo(info.resultType)) + case info: MethodType => info.derivedMethodType(resType = directInfo(info.resultType)) + case info: ExprType => directInfo(info.resultType) + case info => info.member(nme.apply).info + } + + /** A new `m$direct` method to accompany the given method `m` */ + private def newDirectMethod(sym: Symbol)(implicit ctx: Context): Symbol = { + val direct = sym.copy( + name = sym.name.directName, + flags = sym.flags | Synthetic, + info = directInfo(sym.info)) + if (direct.allOverriddenSymbols.isEmpty) direct.resetFlag(Override) + direct + } + + /** The direct method `m$direct` that accompanies the given method `m`. + * Create one if it does not exist already. + */ + private def directMethod(sym: Symbol)(implicit ctx: Context): Symbol = + if (sym.owner.isClass) { + val direct = sym.owner.info.member(sym.name.directName) + .suchThat(_.info matches directInfo(sym.info)).symbol + if (direct.maybeOwner == sym.owner) direct + else newDirectMethod(sym).enteredAfter(thisTransform) + } + else directMeth.getOrElseUpdate(sym, newDirectMethod(sym)) + + + /** Transform `qual.apply` occurrences according to rewrite rule (2) above */ + override def transformSelect(tree: Select)(implicit ctx: Context, info: TransformerInfo) = + if (tree.name == nme.apply && + defn.isImplicitFunctionType(tree.qualifier.tpe.widen) && + shouldBeSpecialized(tree.qualifier.symbol)) { + def directQual(tree: Tree): Tree = tree match { + case Apply(fn, args) => cpy.Apply(tree)(directQual(fn), args) + case TypeApply(fn, args) => cpy.TypeApply(tree)(directQual(fn), args) + case Block(stats, expr) => cpy.Block(tree)(stats, directQual(expr)) + case tree: RefTree => + cpy.Ref(tree)(tree.name.directName) + .withType(directMethod(tree.symbol).termRef) + } + directQual(tree.qualifier) + } else tree + + /** Transform methods with implicit function type result according to rewrite rule (1) above */ + override def transformDefDef(mdef: DefDef)(implicit ctx: Context, info: TransformerInfo): Tree = { + val original = mdef.symbol + if (shouldBeSpecialized(original)) { + val direct = directMethod(original) + + def splitClosure(tree: Tree): (List[Type] => List[List[Tree]] => Tree, Tree) = tree match { + case Block(Nil, expr) => splitClosure(expr) + case Block((meth @ DefDef(nme.ANON_FUN, Nil, clparams :: Nil, _, _)) :: Nil, cl: Closure) => + val tparamSyms = mdef.tparams.map(_.symbol) + val vparamSymss = mdef.vparamss.map(_.map(_.symbol)) + val clparamSyms = clparams.map(_.symbol) + val remappedCore = (ts: List[Type]) => (prefss: List[List[Tree]]) => + meth.rhs + .subst(tparamSyms ::: (vparamSymss.flatten ++ clparamSyms), + ts.map(_.typeSymbol) ::: prefss.flatten.map(_.symbol)) + .changeOwnerAfter(original, direct, thisTransform) + .changeOwnerAfter(meth.symbol, direct, thisTransform) + val forwarder = ref(direct) + .appliedToTypeTrees(tparamSyms.map(ref(_))) + .appliedToArgss(vparamSymss.map(_.map(ref(_))) :+ clparamSyms.map(ref(_))) + val fwdClosure = cpy.Block(tree)(cpy.DefDef(meth)(rhs = forwarder) :: Nil, cl) + (remappedCore, fwdClosure) + case EmptyTree => + (_ => _ => EmptyTree, EmptyTree) + } + + val (remappedCore, fwdClosure) = splitClosure(mdef.rhs) + val originalDef = cpy.DefDef(mdef)(rhs = fwdClosure) + val directDef = polyDefDef(direct.asTerm, remappedCore) + Thicket(originalDef, directDef) + } + else mdef + } + } +} |