Pickle quoted constants to ValueExpr

* Avoid const of unpickling
* Smaller bytecode

Author: nicolasstucki

compiler/src/dotty/tools/dotc/core/Definitions.scala

@@ -639,6 +639,7 @@ class Definitions {
     def QuotedType_apply(implicit ctx: Context) = QuotedType_applyR.symbol
 
   def Unpickler_unpickleExpr = ctx.requiredMethod("scala.runtime.quoted.Unpickler.unpickleExpr")
+  def Unpickler_unpickleValueExpr = ctx.requiredMethod("scala.runtime.quoted.Unpickler.unpickleValueExpr")
   def Unpickler_unpickleType = ctx.requiredMethod("scala.runtime.quoted.Unpickler.unpickleType")
 
   lazy val EqType = ctx.requiredClassRef("scala.Eq")

compiler/src/dotty/tools/dotc/quoted/Toolbox.scala

@@ -4,6 +4,7 @@ import dotty.tools.dotc.ast.Trees._
 import dotty.tools.dotc.ast.tpd
 import dotty.tools.dotc.core.Constants._
 import dotty.tools.dotc.printing.RefinedPrinter
+import dotty.tools.dotc.transform.ReifyQuotes
 
 import scala.quoted.Expr
 import scala.runtime.BoxedUnit

compiler/src/dotty/tools/dotc/transform/ReifyQuotes.scala

@@ -12,6 +12,7 @@ import tasty.TreePickler.Hole
 import MegaPhase.MiniPhase
 import SymUtils._
 import NameKinds._
+import dotty.tools.dotc.ast.tpd.Tree
 import typer.Implicits.SearchFailureType
 
 import scala.collection.mutable
@@ -290,12 +291,28 @@ class ReifyQuotes extends MacroTransformWithImplicits {
       }
       else {
         val (body1, splices) = nested(isQuote = true).split(body)
+        pickledQuote(body1, splices, isType).withPos(quote.pos)
+      }
+    }
+
+    private def pickledQuote(body: Tree, splices: List[Tree], isType: Boolean)(implicit ctx: Context) = {
+      def pickleAsValue[T](value: T) = {
+        ref(defn.Unpickler_unpickleValueExpr)
+          .appliedToType(body.tpe.widen)
+          .appliedTo(Literal(Constant(value)))
+      }
+      def pickleAsTasty() = {
         val meth =
-          if (isType) ref(defn.Unpickler_unpickleType).appliedToType(body1.tpe)
-          else ref(defn.Unpickler_unpickleExpr).appliedToType(body1.tpe.widen)
+          if (isType) ref(defn.Unpickler_unpickleType).appliedToType(body.tpe)
+          else ref(defn.Unpickler_unpickleExpr).appliedToType(body.tpe.widen)
         meth.appliedTo(
-            liftList(PickledQuotes.pickleQuote(body1).map(x => Literal(Constant(x))), defn.StringType),
-            liftList(splices, defn.AnyType)).withPos(quote.pos)
+          liftList(PickledQuotes.pickleQuote(body).map(x => Literal(Constant(x))), defn.StringType),
+          liftList(splices, defn.AnyType))
+      }
+      if (splices.nonEmpty) pickleAsTasty()
+      else ReifyQuotes.toValue(body) match {
+        case Some(value) => pickleAsValue(value)
+        case _ => pickleAsTasty()
       }
     }
 
@@ -473,4 +490,13 @@ class ReifyQuotes extends MacroTransformWithImplicits {
       }
     }
   }
-}
+}
+
+object ReifyQuotes {
+  def toValue(tree: Tree): Option[Any] = tree match {
+    case Literal(Constant(c)) => Some(c)
+    case Block(Nil, e) => toValue(e)
+    case Inlined(_, Nil, e) => toValue(e)
+    case _ => None
+  }
+}

library/src/scala/runtime/quoted/Unpickler.scala

@@ -1,7 +1,7 @@
 package scala.runtime.quoted
 
 import scala.quoted.Types.TastyType
-import scala.quoted.Exprs.TastyExpr
+import scala.quoted.Exprs.{TastyExpr, ValueExpr}
 import scala.quoted.{Expr, Type}
 
 /** Provides methods to unpickle `Expr` and `Type` trees. */
@@ -17,6 +17,9 @@ object Unpickler {
    */
   def unpickleExpr[T](repr: Pickled, args: Seq[Any]): Expr[T] = new TastyExpr[T](repr, args)
 
+  /** Unpickle `value` which represents a pickled `Expr` tree for `value` itself */
+  def unpickleValueExpr[T](value: T): Expr[T] = new ValueExpr[T](value)
+
   /** Unpickle `repr` which represents a pickled `Type` tree,
    *  replacing splice nodes with `args`
    */

tests/run/quote-compile-constants.check

@@ -0,0 +1,12 @@
+class scala.quoted.Exprs$ValueExpr
+class scala.quoted.Exprs$ValueExpr
+class scala.quoted.Exprs$ValueExpr
+class scala.quoted.Exprs$ValueExpr
+class scala.quoted.Exprs$ValueExpr
+class scala.quoted.Exprs$ValueExpr
+class scala.quoted.Exprs$ValueExpr
+class scala.quoted.Exprs$ValueExpr
+class scala.quoted.Exprs$ValueExpr
+class scala.quoted.Exprs$ValueExpr
+class scala.quoted.Exprs$ValueExpr
+class scala.quoted.Exprs$ValueExpr

tests/run/quote-compile-constants.scala

@@ -0,0 +1,18 @@
+import scala.quoted._
+
+object Test {
+  def main(args: Array[String]): Unit = {
+    println(('(true)).getClass)
+    println(('{ 'a' }).getClass)
+    println(('{ '\n' }).getClass)
+    println(('{ '"' }).getClass)
+    println(('{ '\'' }).getClass)
+    println(('{ '\\' }).getClass)
+    println(('(1)).getClass)
+    println(('( { { 2 } } )).getClass)
+    println(('(3L)).getClass)
+    println(('(4.0f)).getClass)
+    println(('(5.0d)).getClass)
+    println(('("xyz")).getClass)
+  }
+}