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allow tree of ConstantType as pattern in switch #6956

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scabug opened this Issue Jan 10, 2013 · 7 comments

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scabug commented Jan 10, 2013

This one is trickier, as it requires the pattern matcher and the backend to agree that tableswitches can be generated for something other than literals:

$ cat testTableSwitch.scala 
package test.switch

object Test {
  private[this] final val ONE = 1

  def switchBad(i: Byte): Int = i match {
    case ONE => 1
    case 2 => 2
    case 3 => 3
    case _ => 0
  }

  def switchOkay(i: Byte): Int = i match {
    case 1 => 1
    case 2 => 2
    case 3 => 3
    case _ => 0
  }
}

$ ../build/quick/bin/scalac testTableSwitch.scala

$ javap -classpath . -c 'test.switch.Test$'
Compiled from "testTableSwitch.scala"
public final class test.switch.Test$ {
  public static final test.switch.Test$ MODULE$;

  public static {};
    Code:
       0: new           #2                  // class test/switch/Test$
       3: invokespecial #12                 // Method "<init>":()V
       6: return        

  public int switchBad(byte);
    Code:
       0: iload_1       
       1: istore_2      
       2: iconst_1      
       3: iload_2       
       4: if_icmpne     15
     ... comparing with each constant ...
      43: iconst_0      
      44: istore        4
      46: iload         4
      48: ireturn       

  public int switchOkay(byte);
    Code:
       0: iload_1       
       1: istore_2      
       2: iload_2       
       3: tableswitch   { // 1 to 3
                     1: 40
                     2: 36
                     3: 32
               default: 28
          }
      28: iconst_0      
      29: goto          41
      32: iconst_3      
      33: goto          41
      36: iconst_2      
      37: goto          41
      40: iconst_1      
      41: ireturn       
}
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scabug commented Jan 10, 2013

Imported From: https://issues.scala-lang.org/browse/SI-6956?orig=1
Reporter: @VladUreche
Affected Versions: 2.10.0

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scabug commented Jan 10, 2013

@paulp said:
What? I can't believe this doesn't work already. The constant folder is supposed to do some folding. This isn't tricky, we just have to expose pattern trees to the constant folder.

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scabug commented Jan 10, 2013

@paulp said:
OH, IT'S ANOTHER REGRESSION. Moors! Life doesn't end after typer!

  public int switchBad(byte);
    flags: ACC_PUBLIC
    Code:
      stack=2, locals=3, args_size=2
         0: iload_1       
         1: istore_2      
         2: iconst_1      
         3: iload_2       
         4: if_icmpne     11
         7: iconst_1      
         8: goto          45
        11: iload_2       
        12: tableswitch   { // 2 to 3
                       2: 40
                       3: 44
                 default: 36
            }
        36: iconst_0      
        37: goto          45
        40: iconst_2      
        41: goto          45
        44: iconst_3      
        45: ireturn       
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scabug commented Jan 15, 2013

@adriaanm said:
which version of scalac produced this bytecode?

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scabug commented Jan 15, 2013

@adriaanm said:
nevermind, 2.10.0 -Xoldpatmat will do fine

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scabug commented Jan 16, 2013

@VladUreche said:
I was using the virtualized pattern matcher and a build of 2.10.0-wip.

@scabug scabug closed this Jan 17, 2013

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scabug commented Jan 17, 2013

@VladUreche said:
Thank you Adriaan and Paul!

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