don't store subpats bound to underscore

also, tweak fix in place for SI-5158 to appease SI-6941
don't store mutable fields from scala.* as we can assume
these classes are well-behaved and do not mutate their
case class fields

5 files changed, 49 insertions, 8 deletions

diff --git a/test/files/jvm/patmat_opt_ignore_underscore.check b/test/files/jvm/patmat_opt_ignore_underscore.check
new file mode 100644
index 0000000000..43f53aba12
--- /dev/null
+++ b/test/files/jvm/patmat_opt_ignore_underscore.check
@@ -0,0 +1 @@
+bytecode identical
diff --git a/test/files/jvm/patmat_opt_ignore_underscore.flags b/test/files/jvm/patmat_opt_ignore_underscore.flags
new file mode 100644
index 0000000000..1182725e86
--- /dev/null
+++ b/test/files/jvm/patmat_opt_ignore_underscore.flags
@@ -0,0 +1 @@
+-optimize
\ No newline at end of file
diff --git a/test/files/jvm/patmat_opt_ignore_underscore/Analyzed_1.scala b/test/files/jvm/patmat_opt_ignore_underscore/Analyzed_1.scala
new file mode 100644
index 0000000000..ac59e41ba7
--- /dev/null
+++ b/test/files/jvm/patmat_opt_ignore_underscore/Analyzed_1.scala
@@ -0,0 +1,30 @@
+// this class's bytecode, compiled under -optimize is analyzed by the test
+// method a's bytecode should be identical to method b's bytecode
+// this is not the best test for shielding against regressing on this particular issue,
+// but it sets the stage for checking the bytecode emitted by the pattern matcher and
+// comparing it to manually tuned code using if/then/else etc.
+class SameBytecode {
+  case class Foo(x: Any, y: String)
+
+  def a = 
+    Foo(1, "a") match {
+      case Foo(_: String, y) => y
+    }
+
+  // this method's body holds the tree that should be generated by the pattern matcher for method a (-Xprint:patmat)
+  // the test checks that bytecode for a and b is identical (modulo line numbers)
+  // we can't diff trees as they are quite different (patmat uses jumps to labels that cannot be expressed in source, for example)
+  // note that the actual tree is quite bad: we do an unnecessary null check, isInstanceOf and local val (x3)
+  // some of these will be fixed soon (the initial null check is for the scrutinee, which is harder to fix in patmat)
+  def b: String = {
+    val x1 = Foo(1, "a")
+    if (x1.ne(null)) {
+      if (x1.x.isInstanceOf[String]) {
+        val x3 = x1.x.asInstanceOf[String]
+        return x1.y
+      }
+    }
+
+    throw new MatchError(x1)
+  }
+}
\ No newline at end of file
diff --git a/test/files/jvm/patmat_opt_ignore_underscore/test.scala b/test/files/jvm/patmat_opt_ignore_underscore/test.scala
new file mode 100644
index 0000000000..6179101a7e
--- /dev/null
+++ b/test/files/jvm/patmat_opt_ignore_underscore/test.scala
@@ -0,0 +1,15 @@
+import scala.tools.partest.BytecodeTest
+
+import scala.tools.nsc.util.JavaClassPath
+import java.io.InputStream
+import scala.tools.asm
+import asm.ClassReader
+import asm.tree.{ClassNode, InsnList}
+import scala.collection.JavaConverters._
+
+object Test extends BytecodeTest {
+  def show: Unit = {
+    val classNode = loadClassNode("SameBytecode")
+    sameBytecode(getMethod(classNode, "a"), getMethod(classNode, "b"))
+  }
+}
diff --git a/test/files/run/t6288.check b/test/files/run/t6288.check
index af6bd5d269..4895c2c007 100644
--- a/test/files/run/t6288.check
+++ b/test/files/run/t6288.check
@@ -11,10 +11,7 @@
       [64]case5()[84]{
         [84]<synthetic> val o7: [84]Option[Int] = [84][84]Case3.unapply([84]x1);
         [84]if ([84]o7.isEmpty.unary_!)
-          [84]{
-            [90]val nr: [90]Int = [90]o7.get;
-            [97][97]matchEnd4([97]())
-          }
+          [97][97]matchEnd4([97]())
         else
           [84][84]case6()
       };
@@ -38,10 +35,7 @@
         [195]<synthetic> val o7: [195]Option[List[Int]] = [195][195]Case4.unapplySeq([195]x1);
         [195]if ([195]o7.isEmpty.unary_!)
           [195]if ([195][195][195][195]o7.get.!=([195]null).&&([195][195][195][195]o7.get.lengthCompare([195]1).==([195]0)))
-            [195]{
-              [201]val nr: [201]Int = [201][201]o7.get.apply([201]0);
-              [208][208]matchEnd4([208]())
-            }
+            [208][208]matchEnd4([208]())
           else
             [195][195]case6()
         else