Remove stack values from aliasing set when being dropped

When entering an exception handler, all values are dropped from the
stack (and the exception value is pushed). The ASM analyzer handles
this by invoking `firstHandlerInstructionFrame.clearStack()`. To
ensure consistent aliasing sets, we need to remove the dropped
values from aliasing sets.

1 files changed, 15 insertions, 0 deletions

diff --git a/src/compiler/scala/tools/nsc/backend/jvm/analysis/AliasingFrame.scala b/src/compiler/scala/tools/nsc/backend/jvm/analysis/AliasingFrame.scala
index 7bbe1e2a49..6ae6eddfef 100644
--- a/src/compiler/scala/tools/nsc/backend/jvm/analysis/AliasingFrame.scala
+++ b/src/compiler/scala/tools/nsc/backend/jvm/analysis/AliasingFrame.scala
@@ -205,6 +205,21 @@ class AliasingFrame[V <: Value](nLocals: Int, nStack: Int) extends Frame[V](nLoc
   }
 
   /**
+   * When entering an exception handler, all values are dropped from the stack (and the exception
+   * value is pushed). The ASM analyzer invokes `firstHandlerInstructionFrame.clearStack()`. To
+   * ensure consistent aliasing sets, we need to remove the dropped values from aliasing sets.
+   */
+  override def clearStack(): Unit = {
+    var i = getLocals
+    val end = i + getStackSize
+    while (i < end) {
+      removeAlias(i)
+      i += 1
+    }
+    super.clearStack()
+  }
+
+  /**
    * Merge the AliasingFrame `other` into this AliasingFrame.
    *
    * Aliases that are common in both frames are kept. Example: