Allow beta-reduction on pure inlined blocks

Author: nicolasstucki

compiler/src/dotty/tools/dotc/inlines/InlineReducer.scala

@@ -165,12 +165,6 @@ class InlineReducer(inliner: Inliner)(using Context):
     case Apply(Select(cl, nme.apply), args) if defn.isFunctionType(cl.tpe) =>
       val bindingsBuf = new DefBuffer
       def recur(cl: Tree): Option[Tree] = cl match
-        case Inlined(call, bindings, expr) if bindings.forall(isPureBinding) =>
-          recur(expr).map(cpy.Inlined(cl)(call, bindings, _))
-        case Block(Nil, expr) =>
-          recur(expr).map(cpy.Block(cl)(Nil, _))
-        case Typed(expr, tpt) =>
-          recur(expr).map(cpy.Typed(cl)(_, tpt))
         case Block((ddef : DefDef) :: Nil, closure: Closure) if ddef.symbol == closure.meth.symbol =>
           ddef.tpe.widen match
             case mt: MethodType if ddef.paramss.head.length == args.length =>
@@ -190,6 +184,12 @@ class InlineReducer(inliner: Inliner)(using Context):
                 substTo = argSyms)
               Some(expander.transform(ddef.rhs))
             case _ => None
+        case Block(stats, expr) if stats.forall(isPureBinding) =>
+          recur(expr).map(cpy.Block(cl)(stats, _))
+        case Inlined(call, bindings, expr) if bindings.forall(isPureBinding) =>
+          recur(expr).map(cpy.Inlined(cl)(call, bindings, _))
+        case Typed(expr, tpt) =>
+          recur(expr)
         case _ => None
       recur(cl) match
         case Some(reduced) =>

compiler/test/dotty/tools/backend/jvm/InlineBytecodeTests.scala

@@ -600,10 +600,12 @@ class InlineBytecodeTests extends DottyBytecodeTest {
       val instructions = instructionsFromMethod(fun)
       val expected = // TODO room for constant folding
         List(
-          Op(ICONST_1),
+          Op(ICONST_2),
           VarOp(ISTORE, 1),
+          Op(ICONST_1),
+          VarOp(ISTORE, 2),
           Op(ICONST_2),
-          VarOp(ILOAD, 1),
+          VarOp(ILOAD, 2),
           Op(IADD),
           Op(ICONST_3),
           Op(IADD),

tests/pos/i16374c.scala

@@ -0,0 +1,7 @@
+def method(using String): String = ???
+
+inline def inlineMethod(inline op: String => Unit)(using String): Unit =
+  println({ val a: Int = 1; op }.apply(method))
+
+def test(using String) =
+  inlineMethod(c => print(c))

tests/pos/i16374d.scala

@@ -0,0 +1,4 @@
+inline def inline1(inline f: Int => Int): Int => Int = i => f(1)
+inline def inline2(inline f: Int => Int): Int = f(2) + 3
+def test: Int = inline2(inline1(2.+))
+