Dotty backend fails to emit code in CSE'd if predicate

[jvican]

Code snippet:

final def sum[B](implicit num: Numeric[B]): B = {
           // arithmetic series formula  can be used for regular addition
       var cse: scala.math.Numeric.type = null.asInstanceOf[scala.math.Numeric.type]   
       if ({cse = scala.math.Numeric; num eq cse.IntIsIntegral}||
               (num eq cse.BigIntIsIntegral)||
               (num eq cse.ShortIsIntegral)||
               (num eq cse.ByteIsIntegral)||
               (num eq cse.CharIsIntegral)||
               (num eq cse.LongIsIntegral)||
               (num eq cse.FloatAsIfIntegral)||
               (num eq cse.BigDecimalIsFractional)||
               (num eq cse.DoubleAsIfIntegral)) {     
        null.asInstanceOf[B]
      } else null.asInstanceOf[B]
} 

REPL fails with:

error: Error while emitting line35$object$$iw$$iw$
1

The Linker (in the branch cse-rebase, that implements Common Subexpression Elimination) fails with a more concise error:

java.lang.ArrayIndexOutOfBoundsException: 1
    at scala.tools.asm.Frame.merge(Frame.java:1397)
    at scala.tools.asm.Frame.merge(Frame.java:1352)
    at scala.tools.asm.MethodWriter.visitMaxs(MethodWriter.java:1483)
    at scala.tools.asm.tree.MethodNode.accept(MethodNode.java:834)
    at scala.tools.asm.tree.MethodNode.accept(MethodNode.java:726)
    at scala.tools.asm.tree.ClassNode.accept(ClassNode.java:412)
    at dotty.tools.backend.jvm.GenBCodePipeline$Worker2.getByteArray$1(GenBCode.scala:272)
    at dotty.tools.backend.jvm.GenBCodePipeline$Worker2.addToQ3(GenBCode.scala:279)
    at dotty.tools.backend.jvm.GenBCodePipeline$Worker2.run(GenBCode.scala:258)
    at dotty.tools.backend.jvm.GenBCodePipeline.buildAndSendToDisk(GenBCode.scala:361)
    at dotty.tools.backend.jvm.GenBCodePipeline.run(GenBCode.scala:324)
    at dotty.tools.backend.jvm.GenBCode.run(GenBCode.scala:56)
    at dotty.tools.dotc.core.Phases$Phase$$anonfun$runOn$1.apply(Phases.scala:279)
    at dotty.tools.dotc.core.Phases$Phase$$anonfun$runOn$1.apply(Phases.scala:277)
    at scala.collection.immutable.List.map(List.scala:273)
    at dotty.tools.dotc.core.Phases$Phase$class.runOn(Phases.scala:277)
    at dotty.tools.backend.jvm.GenBCode.runOn(GenBCode.scala:40)
    at dotty.tools.dotc.Run$$anonfun$compileUnits$1$$anonfun$apply$mcV$sp$1.apply(Run.scala:62)
    at dotty.tools.dotc.Run$$anonfun$compileUnits$1$$anonfun$apply$mcV$sp$1.apply(Run.scala:59)
    at scala.collection.IndexedSeqOptimized$class.foreach(IndexedSeqOptimized.scala:33)
    at scala.collection.mutable.ArrayOps$ofRef.foreach(ArrayOps.scala:186)
    at dotty.tools.dotc.Run$$anonfun$compileUnits$1.apply$mcV$sp(Run.scala:59)
    at dotty.tools.dotc.Run$$anonfun$compileUnits$1.apply(Run.scala:54)
    at dotty.tools.dotc.Run$$anonfun$compileUnits$1.apply(Run.scala:54)
    at dotty.tools.dotc.util.Stats$.monitorHeartBeat(Stats.scala:69)
    at dotty.tools.dotc.Run.compileUnits(Run.scala:54)
    at dotty.tools.dotc.Run.compileSources(Run.scala:51)
    at dotty.tools.dotc.Run.compile(Run.scala:35)
    at dotty.tools.dotc.Driver.doCompile(Driver.scala:26)
    at dotty.tools.dotc.Driver.process(Driver.scala:124)
    at dotty.tools.dotc.Driver.process(Driver.scala:93)
    at dotty.tools.dotc.Driver.process(Driver.scala:105)
    at test.CompilerTest.compileArgs(CompilerTest.scala:237)
    at test.CompilerTest.compileFile(CompilerTest.scala:106)
    at dotc.tests.dotty(tests.scala:151)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:498)
    at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:47)
    at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:12)
    at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:44)
    at org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:17)
    at org.junit.runners.ParentRunner.runLeaf(ParentRunner.java:271)
    at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:70)
    at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:50)
    at org.junit.runners.ParentRunner$3.run(ParentRunner.java:238)
    at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:63)
    at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:236)
    at org.junit.runners.ParentRunner.access$000(ParentRunner.java:53)
    at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:229)
    at org.junit.runners.ParentRunner.run(ParentRunner.java:309)
    at org.junit.runners.Suite.runChild(Suite.java:127)
    at org.junit.runners.Suite.runChild(Suite.java:26)
    at org.junit.runners.ParentRunner$3.run(ParentRunner.java:238)
    at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:63)
    at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:236)
    at org.junit.runners.ParentRunner.access$000(ParentRunner.java:53)
    at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:229)
    at org.junit.runners.ParentRunner.run(ParentRunner.java:309)
    at org.junit.runner.JUnitCore.run(JUnitCore.java:160)
    at org.junit.runner.JUnitCore.run(JUnitCore.java:138)
    at com.novocode.junit.JUnitRunner$1.execute(JUnitRunner.java:132)
    at sbt.ForkMain$Run$2.call(ForkMain.java:296)
    at sbt.ForkMain$Run$2.call(ForkMain.java:286)
    at java.util.concurrent.FutureTask.run(FutureTask.java:266)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
    at java.lang.Thread.run(Thread.java:745)
error: Error while emitting scala/collection/immutable/NumericRange
1

It seems to me that this code should compile. Therefore, I consider this a bug. The original source code is located in the Numeric class of the Scala standard library.

[DarkDimius]

For future reference. I've introduced an undocumented environment variable printBCODE, that specifies which methods to print.
In this example:

printBCODE=sum dotc bfail.scala
Bytecode for method sum
   L0
    LINENUMBER 2 L0
   L1
    LINENUMBER 4 L1
    ACONST_NULL
    CHECKCAST scala/math/Numeric$
   L2
    ASTORE 2
   L3
    LINENUMBER 5 L3
    GETSTATIC scala/math/Numeric$.MODULE$ : Lscala/math/Numeric$;
    ASTORE 2
    ALOAD 1
    ALOAD 2
    GETSTATIC scala/math/Numeric$IntIsIntegral$.MODULE$ : Lscala/math/Numeric$IntIsIntegral$;
    IF_ACMPEQ L4
    GOTO L5
   L4
    ICONST_1
    GOTO L6
   L5
    ICONST_0
   L6
    IFNE L7
    GOTO L8
   L8
    LINENUMBER 6 L8
    ALOAD 1
    ALOAD 2
    GETSTATIC scala/math/Numeric$BigIntIsIntegral$.MODULE$ : Lscala/math/Numeric$BigIntIsIntegral$;
    IF_ACMPEQ L7
    GOTO L9
   L9
    LINENUMBER 7 L9
    ALOAD 1
    ALOAD 2
    GETSTATIC scala/math/Numeric$ShortIsIntegral$.MODULE$ : Lscala/math/Numeric$ShortIsIntegral$;
    IF_ACMPEQ L7
    GOTO L10
   L10
    LINENUMBER 8 L10
    ALOAD 1
    ALOAD 2
    GETSTATIC scala/math/Numeric$ByteIsIntegral$.MODULE$ : Lscala/math/Numeric$ByteIsIntegral$;
    IF_ACMPEQ L7
    GOTO L11
   L11
    LINENUMBER 9 L11
    ALOAD 1
    ALOAD 2
    GETSTATIC scala/math/Numeric$CharIsIntegral$.MODULE$ : Lscala/math/Numeric$CharIsIntegral$;
    IF_ACMPEQ L7
    GOTO L12
   L12
    LINENUMBER 10 L12
    ALOAD 1
    ALOAD 2
    GETSTATIC scala/math/Numeric$LongIsIntegral$.MODULE$ : Lscala/math/Numeric$LongIsIntegral$;
    IF_ACMPEQ L7
    GOTO L13
   L13
    LINENUMBER 11 L13
    ALOAD 1
    ALOAD 2 
    // HERE IS THE BUG.
    GETSTATIC scala/math/Numeric$FloatAsIfIntegral$.MODULE$ : Lscala/math/Numeric$FloatAsIfIntegral$;
    IF_ACMPEQ L7
    GOTO L14
   L14
    LINENUMBER 12 L14
    ALOAD 1
    ALOAD 2
    GETSTATIC scala/math/Numeric$BigDecimalIsFractional$.MODULE$ : Lscala/math/Numeric$BigDecimalIsFractional$;
    IF_ACMPEQ L7
    GOTO L15
   L15
    LINENUMBER 13 L15
    ALOAD 1
    ALOAD 2
    GETSTATIC scala/math/Numeric$DoubleAsIfIntegral$.MODULE$ : Lscala/math/Numeric$DoubleAsIfIntegral$;
    IF_ACMPEQ L7
    GOTO L16
   L7
    LINENUMBER 14 L7
    ACONST_NULL
    POP
    ACONST_NULL
    GOTO L17
   L16
    LINENUMBER 15 L16
    ACONST_NULL
    POP
    ACONST_NULL
   L17
    ARETURN
   L18
    LOCALVARIABLE cse Lscala/math/Numeric$; L2 L17 2
    LOCALVARIABLE this LTest$; L1 L18 0
    LOCALVARIABLE num Lscala/math/Numeric; L1 L18 1
    MAXSTACK = 0
    MAXLOCALS = 0