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>> behaves like >>> when inlined #10037

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scabug opened this issue Nov 9, 2016 · 4 comments
Closed

>> behaves like >>> when inlined #10037

scabug opened this issue Nov 9, 2016 · 4 comments
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@som-snytt
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help wanted optimizer
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2.11.11

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@scabug
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scabug commented Nov 9, 2016

Hey all,

It looks like >> is acting like >>> when inlined.

This bug showed up in an sbt 0.13.12 project running Scala 2.11.8. I compiled a file containing this object, with -optimize enabled:

object Bug {
  @inline def inlineShift(x: Int): Int = x >> 1
  def shift(x: Int): Int = x >> 1
}

Then started a console with sbt console, and found the following discrepancy between the behavior of the two functions:

scala> Bug.inlineShift(Int.MinValue)
res0: Int = 1073741824

scala> Bug.shift(Int.MinValue)
res1: Int = -1073741824

scala> Int.MinValue
res2: Int = -2147483648

The functions both returned Int.MinValue when I removed the -optimize flag.
@scabug
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scabug commented Nov 9, 2016

Imported From: https://issues.scala-lang.org/browse/SI-10037?orig=1
Reporter: Sam Ritchie (sritchie)
Affected Versions: 2.11.8

@scabug
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scabug commented Nov 9, 2016

Sam Ritchie (sritchie) said:
Sorry for all the edits. I can't figure out how to format the first block of code.

@scabug
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scabug commented Nov 9, 2016

@som-snytt said:

GenASM and separate compilation:

$ ~/scala-2.11.8/bin/scalac -optimize -Ybackend:GenBCode shifted.scala && ~/scala-2.11.8/bin/scala -optimize -Ybackend:GenBCode
Welcome to Scala 2.11.8 (Java HotSpot(TM) 64-Bit Server VM, Java 1.8.0_101).
Type in expressions for evaluation. Or try :help.

scala> shifted.Bug.inlineShift(Int.MinValue)
res0: Int = -1073741824

scala> :quit
$ rm shifted/*.class
$ ~/scala-2.11.8/bin/scalac -optimize -Ybackend:GenASM shifted.scala && ~/scala-2.11.8/bin/scala -optimize -Ybackend:GenASM
Welcome to Scala 2.11.8 (Java HotSpot(TM) 64-Bit Server VM, Java 1.8.0_101).
Type in expressions for evaluation. Or try :help.

scala> shifted.Bug.inlineShift(Int.MinValue)
res0: Int = 1073741824

scala> :quit
amarki@amarki-462836:~/tmp$ ~/scala-2.11.8/bin/scalac -optimize shifted.scala && ~/scala-2.11.8/bin/scala shifted.Test
-1073741824
-1073741824
amarki@amarki-462836:~/tmp$ cat shifted.scala

package shifted

object Bug {
  @inline def inlineShift(x: Int): Int = x >> 1
  def shift(x: Int): Int = x >> 1
  def f(x: Int): Int = inlineShift(x)    // ok
}

object Test extends App {
  println(Bug.inlineShift(Int.MinValue))   // ok
  println(Bug.shift(Int.MinValue))
}

@scabug
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scabug commented Nov 10, 2016

@som-snytt said:
scala/scala#5518

@scabug scabug closed this as completed Nov 11, 2016
@scabug scabug added this to the 2.11.9 milestone Apr 7, 2017
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