Add tests example of a partally unrolled loop

Author: nicolasstucki

tests/run/quote-unrolled-foreach.check

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+<log> start loop
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+<log> start loop
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+<log> start loop
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+<log> start loop
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+<log> start loop
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+<log> start loop
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tests/run/quote-unrolled-foreach/quoted_1.scala

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+import scala.annotation.tailrec
+import scala.quoted._
+
+object Macro {
+
+  inline def unrolledForeach(inline unrollSize: Int, seq: Array[Int])(f: => Int => Unit): Unit = // or f: Int => Unit
+    ~unrolledForeachImpl(unrollSize, '(seq), '(f))
+
+  private def unrolledForeachImpl(unrollSize: Int, seq: Expr[Array[Int]], f: Expr[Int => Unit]): Expr[Unit] = '{
+    val size = (~seq).length
+    assert(size % (~unrollSize.toExpr) == 0) // for simplicity of the implementation
+    var i = 0
+    while (i < size) {
+      println("<log> start loop")
+      ~{
+        for (j <- new UnrolledRange(0, unrollSize)) '{
+          val element = (~seq)(i + ~j.toExpr)
+          ~f('(element)) // or `(~f)(element)` if `f` should not be inlined
+        }
+      }
+      i += ~unrollSize.toExpr
+    }
+
+  }
+
+  private class UnrolledRange(start: Int, end: Int) {
+    def foreach(f: Int => Expr[Unit]): Expr[Unit] = {
+      @tailrec def loop(i: Int, acc: Expr[Unit]): Expr[Unit] =
+        if (i >= 0) loop(i - 1, '{ ~f(i); ~acc })
+        else acc
+      loop(end - 1, '())
+    }
+  }
+}

tests/run/quote-unrolled-foreach/quoted_2.scala

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+
+import scala.quoted._
+
+object Test {
+  def main(args: Array[String]): Unit = {
+    val arr = Array.tabulate[Int](21)(x => x)
+    Macro.unrolledForeach(3, arr) { (x: Int) =>
+      System.out.println(2 * x)
+    }
+
+    /* unrooled code:
+
+      val size: Int = arr.length()
+      assert(size % 3 == 0)
+      var i: Int = 0
+      while (i < size) {
+        println("<log> start loop")
+        val element$1: Int = arr(i)
+        val x$1: Int = element$1
+        System.out.println(2 * x$1)
+        val element$2: Int = arr(i + 1)
+        val x$2: Int = element$2
+        System.out.println(2 * x$2)
+        val element$3: Int = arr(i + 2)
+        val x$3: Int = element$3
+        System.out.println(2 * x$3)
+        i = i + 3
+      }
+    */
+  }
+
+}