[Mono-bugs] [Bug 686433] New: (0 - x) == x according to dmcs. bad constant folding.

[bugzilla_noreply at novell.com]

https://bugzilla.novell.com/show_bug.cgi?id=686433

https://bugzilla.novell.com/show_bug.cgi?id=686433#c0


           Summary: (0 - x) == x according to dmcs. bad constant folding.
    Classification: Mono
           Product: Mono: Compilers
           Version: 2.10.x
          Platform: Macintosh
        OS/Version: Mac OS X 10.6
            Status: NEW
          Severity: Critical
          Priority: P5 - None
         Component: C#
        AssignedTo: msafar at novell.com
        ReportedBy: brian at sooloos.com
         QAContact: mono-bugs at lists.ximian.com
          Found By: ---
           Blocker: ---


User-Agent:       Mozilla/5.0 (Macintosh; Intel Mac OS X 10_6_7)
AppleWebKit/534.28 (KHTML, like Gecko) Chrome/12.0.725.0 Safari/534.28

I could not believe this when I saw it...

it looks like bad constant folding in the compiler. (0 - x) is being
transformed into (x) when C# is compiled to IL. This is with 2.10.1 on macos x
10.6.7.

brian at brianmbp ~ $ cat t.cs                                                     
using System;
class Foo {
    public static void Main(string[] args) {
        int foo = 32 * 1024;
        Console.WriteLine("   - foo = {0}",   - foo);
        Console.WriteLine("0 - foo = {0}", 0 - foo);
    }
}
brian at brianmbp ~ $ dmcs t.cs && mono t.exe
   - foo = -32768
0 - foo = 32768
brian at brianmbp ~ $ monodis t.exe          
assembly extern mscorlib
{
  .ver 4:0:0:0
  .publickeytoken = (B7 7A 5C 56 19 34 E0 89 ) // .z\V.4..
}
assembly 't'
{
  .custom instance void class
[mscorlib]System.Runtime.CompilerServices.RuntimeCompatibilityAttribute::'.ctor'()
=  (
        01 00 01 00 54 02 16 57 72 61 70 4E 6F 6E 45 78   // ....T..WrapNonEx
        63 65 70 74 69 6F 6E 54 68 72 6F 77 73 01       ) // ceptionThrows.

  .hash algorithm 0x00008004
  .ver  0:0:0:0
}
module t.exe // GUID = {E0608D43-1541-4796-AA7C-B49D16107C31}


  .class private auto ansi beforefieldinit Foo
      extends [mscorlib]System.Object
  {

    // method line 1
    .method public hidebysig specialname rtspecialname 
           instance default void '.ctor' ()  cil managed 
    {
        // Method begins at RVA 0x20ec
    // Code size 7 (0x7)
    .maxstack 8
    IL_0000:  ldarg.0 
    IL_0001:  call instance void object::'.ctor'()
    IL_0006:  ret 
    } // end of method Foo::.ctor

    // method line 2
    .method public static hidebysig 
           default void Main (string[] args)  cil managed 
    {
        // Method begins at RVA 0x20f4
    .entrypoint
    // Code size 40 (0x28)
    .maxstack 4
    .locals init (
        int32    V_0)
    IL_0000:  ldc.i4 32768
    IL_0005:  stloc.0 
    IL_0006:  ldstr "  - foo = {0}"
    IL_000b:  ldloc.0 
    IL_000c:  neg 
    IL_000d:  box [mscorlib]System.Int32
    IL_0012:  call void class [mscorlib]System.Console::WriteLine(string,
object)
    IL_0017:  ldstr "0 - foo = {0}"
    IL_001c:  ldloc.0 
    IL_001d:  box [mscorlib]System.Int32
    IL_0022:  call void class [mscorlib]System.Console::WriteLine(string,
object)
    IL_0027:  ret 
    } // end of method Foo::Main

  } // end of class Foo


Reproducible: Always

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