Merge pull request #2954 from retronym/ticket/7852

Avoid null checks when emitting "".== and SomeModule.==

3 files changed, 40 insertions, 0 deletions

diff --git a/test/files/run/t7852.check b/test/files/run/t7852.check
new file mode 100644
index 0000000000..e69de29bb2
--- /dev/null
+++ b/test/files/run/t7852.check
diff --git a/test/files/run/t7852.flags b/test/files/run/t7852.flags
new file mode 100644
index 0000000000..f6262fd3e0
--- /dev/null
+++ b/test/files/run/t7852.flags
@@ -0,0 +1 @@
+-Ynooptimise
diff --git a/test/files/run/t7852.scala b/test/files/run/t7852.scala
new file mode 100644
index 0000000000..c93db718fd
--- /dev/null
+++ b/test/files/run/t7852.scala
@@ -0,0 +1,39 @@
+import scala.tools.partest.BytecodeTest
+import scala.tools.asm
+import scala.tools.asm.util._
+import scala.tools.nsc.util.stringFromWriter
+import scala.collection.JavaConverters._
+
+object Test extends BytecodeTest {
+  val nullChecks = Set(asm.Opcodes.IFNONNULL, asm.Opcodes.IFNULL)
+
+  def show: Unit = {
+    def test(methodName: String, expected: Int) {
+      val classNode = loadClassNode("Lean")
+      val methodNode = getMethod(classNode, methodName)
+      val got = countNullChecks(methodNode.instructions)
+      assert(got == expected, s"expected $expected but got $got comparisons")
+    }
+    test("string", expected = 0)
+    test("module", expected = 0)
+    test("moduleIndirect", expected = 2)
+  }
+
+  def countNullChecks(insnList: asm.tree.InsnList): Int =
+    insnList.iterator.asScala.map(_.getOpcode).count(nullChecks)
+}
+
+class Lean {
+  def string {
+    "" == toString
+  }
+
+  def module {
+    Nil == (toString: Any)
+  }
+
+  def moduleIndirect {
+    val n: Nil.type = null
+    n == (toString: Any) // still need null checks here.
+  }
+}