SI-9315 Desugar string concat to java.lang.StringBuilder ...

... instead of scala.collection.mutable.StringBuilder to benefit from
JVM optimizations. Unfortunately primitives are already boxed in erasure
when they end up in this part of the backend.

1 files changed, 70 insertions, 0 deletions

diff --git a/test/junit/scala/tools/nsc/backend/jvm/StringConcatTest.scala b/test/junit/scala/tools/nsc/backend/jvm/StringConcatTest.scala
new file mode 100644
index 0000000000..80cde6c9a9
--- /dev/null
+++ b/test/junit/scala/tools/nsc/backend/jvm/StringConcatTest.scala
@@ -0,0 +1,70 @@
+package scala.tools.nsc
+package backend.jvm
+
+import org.junit.runner.RunWith
+import org.junit.runners.JUnit4
+import org.junit.Test
+import scala.tools.asm.Opcodes._
+import org.junit.Assert._
+
+import scala.tools.testing.AssertUtil._
+
+import CodeGenTools._
+import scala.tools.partest.ASMConverters
+import ASMConverters._
+import scala.tools.testing.ClearAfterClass
+
+object StringConcatTest extends ClearAfterClass.Clearable {
+  var compiler = newCompiler()
+  def clear(): Unit = { compiler = null }
+}
+
+@RunWith(classOf[JUnit4])
+class StringConcatTest extends ClearAfterClass {
+  ClearAfterClass.stateToClear = StringConcatTest
+  val compiler = StringConcatTest.compiler
+
+  val commonPreInstructions = List(Label(0), LineNumber(1, Label(0)), TypeOp(NEW, "java/lang/StringBuilder"), Op(DUP), Invoke(INVOKESPECIAL, "java/lang/StringBuilder", "<init>", "()V", false), Ldc(LDC, "abc"), Invoke(INVOKEVIRTUAL, "java/lang/StringBuilder", "append", "(Ljava/lang/String;)Ljava/lang/StringBuilder;", false), VarOp(ALOAD, 0))
+
+  val commonPostInstructions = List(Invoke(INVOKEVIRTUAL, "java/lang/StringBuilder", "toString", "()Ljava/lang/String;", false), Op(ARETURN), Label(12))
+
+  def instructionsWithCommonParts(instructions: List[Instruction]) = commonPreInstructions ++ instructions ++ commonPostInstructions
+
+  def instructionsForResultMethod(code: String): List[Instruction] = {
+    val methods = compileMethods(compiler)(code)
+    val resultMethod = methods.find(_.name == "result").get
+    instructionsFromMethod(resultMethod)
+  }
+
+  @Test
+  def concatStringToStringBuilder: Unit = {
+    val code = """ def string = "def"; def result = "abc" + string """
+    val actualInstructions = instructionsForResultMethod(code)
+    val expectedInstructions = instructionsWithCommonParts(List(Invoke(INVOKEVIRTUAL, "C", "string", "()Ljava/lang/String;", false), Invoke(INVOKEVIRTUAL, "java/lang/StringBuilder", "append", "(Ljava/lang/String;)Ljava/lang/StringBuilder;", false)))
+    assertSameCode(actualInstructions, expectedInstructions)
+  }
+
+  @Test
+  def concatStringBufferToStringBuilder: Unit = {
+    val code = """ def stringBuffer = new java.lang.StringBuffer("def"); def result = "abc" + stringBuffer """
+    val actualInstructions = instructionsForResultMethod(code)
+    val expectedInstructions = instructionsWithCommonParts(List(Invoke(INVOKEVIRTUAL, "C", "stringBuffer", "()Ljava/lang/StringBuffer;", false), Invoke(INVOKEVIRTUAL, "java/lang/StringBuilder", "append", "(Ljava/lang/StringBuffer;)Ljava/lang/StringBuilder;", false)))
+    assertSameCode(actualInstructions, expectedInstructions)
+  }
+
+  @Test
+  def concatCharSequenceToStringBuilder: Unit = {
+    val code = """ def charSequence: CharSequence = "def"; def result = "abc" + charSequence """
+    val actualInstructions = instructionsForResultMethod(code)
+    val expectedInstructions = instructionsWithCommonParts(List(Invoke(INVOKEVIRTUAL, "C", "charSequence", "()Ljava/lang/CharSequence;", false), Invoke(INVOKEVIRTUAL, "java/lang/StringBuilder", "append", "(Ljava/lang/CharSequence;)Ljava/lang/StringBuilder;", false)))
+    assertSameCode(actualInstructions, expectedInstructions)
+  }
+
+  @Test
+  def concatIntToStringBuilder: Unit = {
+    val code = """ def int = 123; def result = "abc" + int """
+    val actualInstructions = instructionsForResultMethod(code)
+    val expectedInstructions = instructionsWithCommonParts(List(Invoke(INVOKEVIRTUAL, "C", "int", "()I", false), Invoke(INVOKESTATIC, "scala/runtime/BoxesRunTime", "boxToInteger", "(I)Ljava/lang/Integer;", false), Invoke(INVOKEVIRTUAL, "java/lang/StringBuilder", "append", "(Ljava/lang/Object;)Ljava/lang/StringBuilder;", false)))
+    assertSameCode(actualInstructions, expectedInstructions)
+  }
+}