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Crash in dead code elimination: could not find init #8334

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scabug opened this Issue Feb 24, 2014 · 4 comments

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scabug commented Feb 24, 2014

Rex ran into it while working on optimizing List operations. Minimized version looks like this:

package abc

class Bar(head: AnyRef)

class A {
  @inline
  final def mapp(f: AnyRef => AnyRef): AnyRef = {
    new Bar(f(null))
  }
  def f: Boolean = {
    mapp (_ => return false)
    true
  }
}

when compiled with -optimize we get:

error: could not find init in: abc.A.f
error: scala.reflect.internal.FatalError:
  could not find init in: abc.A.f
     while compiling: OptimizerCrash.scala
        during phase: dce
[..]

== Source file context for tree position ==

    11   }
    12   def f: Boolean = {
    13     mapp (_ => return false)
    14     true
    15   }
    16 }
	at scala.reflect.internal.SymbolTable.abort(SymbolTable.scala:57)
	at scala.tools.nsc.Global.abort(Global.scala:268)
	at scala.tools.nsc.backend.opt.DeadCodeElimination$DeadCode.scala$tools$nsc$backend$opt$DeadCodeElimination$DeadCode$$findInstruction(DeadCodeElimination.scala:432)
	at scala.tools.nsc.backend.opt.DeadCodeElimination$DeadCode.mark(DeadCodeElimination.scala:261)
	at scala.tools.nsc.backend.opt.DeadCodeElimination$DeadCode.dieCodeDie(DeadCodeElimination.scala:103)
	at scala.tools.nsc.backend.opt.DeadCodeElimination$DeadCode$$anonfun$analyzeClass$2.apply(DeadCodeElimination.scala:60)
	at scala.tools.nsc.backend.opt.DeadCodeElimination$DeadCode$$anonfun$analyzeClass$2.apply(DeadCodeElimination.scala:58)
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scabug commented Feb 24, 2014

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scabug commented Feb 24, 2014

@gkossakowski said (edited on Feb 25, 2014 12:27:07 AM UTC):
Things go south in inliner, if you check icode after inliner phase (with -Xprint-icode) you'll see:

class A extends Object {
  // fields:
  
  // methods
  def mapp(f: Function1 (REF(trait Function1))): Object {
  locals: value f
  startBlock: 1
  blocks: [1]
  
  1: 
    8	NEW REF(class Bar)
    8	DUP(REF(class Bar))
    8	LOAD_LOCAL(value f)
    8	CONSTANT(null)
    8	CALL_METHOD scala.Function1.apply (dynamic)
    8	CALL_METHOD abc.Bar.<init> (static-instance)
    8	RETURN(REF(class Object))

def f(): Boolean {

[...]
    
  9: 
    11	NEW REF(class Bar)
    11	DUP(REF(class Bar))
    11	LOAD_LOCAL(variable f1)
    11	CONSTANT(null)
// whoops, where are my two method calls that should be copied from block 1 seen above?
    11	STORE_LOCAL(variable v11)
    11	STORE_LOCAL(variable $inlThis2)
    11	JUMP 11
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scabug commented Aug 28, 2015

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scabug commented Aug 28, 2015

@lrytz said:
fixed in new optimizer, test in scala/scala#4711

@scabug scabug closed this Jan 27, 2016

@scabug scabug added the critical label Apr 7, 2017

@scabug scabug added this to the 2.12.0-M4 milestone Apr 7, 2017

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