Prevent infinite recursion in ProdConsAnalyzer

When an instruction is its own producer or consumer, the
`initialProducer` / `ultimateConsumer` methods would loop.
While loops or @tailrec annotated methods can generate such bytecode.

1 files changed, 42 insertions, 0 deletions

diff --git a/test/junit/scala/tools/nsc/backend/jvm/analysis/ProdConsAnalyzerTest.scala b/test/junit/scala/tools/nsc/backend/jvm/analysis/ProdConsAnalyzerTest.scala
index 9af9ef54fc..a5b3faced8 100644
--- a/test/junit/scala/tools/nsc/backend/jvm/analysis/ProdConsAnalyzerTest.scala
+++ b/test/junit/scala/tools/nsc/backend/jvm/analysis/ProdConsAnalyzerTest.scala
@@ -246,4 +246,46 @@ class ProdConsAnalyzerTest extends ClearAfterClass {
     testSingleInsn(a.consumersOfOutputsFrom(l2i), "IRETURN")
     testSingleInsn(a.producersForInputsOf(ret), "L2I")
   }
+
+  @Test
+  def cyclicProdCons(): Unit = {
+    import Opcodes._
+    val m = genMethod(descriptor = "(I)I")(
+      Label(1),
+      VarOp(ILOAD, 1),
+      IntOp(BIPUSH, 10),
+      Op(IADD),          // consumer of the above ILOAD
+
+      Op(ICONST_0),
+      Jump(IF_ICMPNE, Label(2)),
+
+      VarOp(ILOAD, 1),
+      VarOp(ISTORE, 1),
+      Jump(GOTO, Label(1)),
+
+      Label(2),
+      IntOp(BIPUSH, 9),
+      Op(IRETURN)
+    )
+    m.maxLocals = 2
+    m.maxStack = 2
+    val a = new ProdConsAnalyzer(m, "C")
+
+    val List(iadd) = findInstr(m, "IADD")
+    val firstLoad = iadd.getPrevious.getPrevious
+    assert(firstLoad.getOpcode == ILOAD)
+    val secondLoad = findInstr(m, "ISTORE").head.getPrevious
+    assert(secondLoad.getOpcode == ILOAD)
+
+    testSingleInsn(a.producersForValueAt(iadd, 2), "ILOAD")
+    testSingleInsn(a.initialProducersForValueAt(iadd, 2), "ParameterProducer(1)")
+    testMultiInsns(a.producersForInputsOf(firstLoad), List("ParameterProducer", "ISTORE"))
+    testMultiInsns(a.producersForInputsOf(secondLoad), List("ParameterProducer", "ISTORE"))
+
+    testSingleInsn(a.ultimateConsumersOfOutputsFrom(firstLoad), "IADD")
+    testSingleInsn(a.ultimateConsumersOfOutputsFrom(secondLoad), "IADD")
+
+    testSingleInsn(a.consumersOfOutputsFrom(firstLoad), "IADD")
+    testSingleInsn(a.consumersOfOutputsFrom(secondLoad), "ISTORE")
+  }
 }