[Mono-bugs] [Bug 78314][Maj] New - Register allocation bug when compiling shift-left operator in very simple loop

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Changed by bbjamey at gmail.com.

http://bugzilla.ximian.com/show_bug.cgi?id=78314

--- shadow/78314	2006-05-06 11:26:14.000000000 -0400
+++ shadow/78314.tmp.32413	2006-05-06 11:26:14.000000000 -0400
@@ -0,0 +1,121 @@
+Bug#: 78314
+Product: Mono: Runtime
+Version: 1.1
+OS: 
+OS Details: 
+Status: NEW   
+Resolution: 
+Severity: 
+Priority: Major
+Component: JIT
+AssignedTo: lupus at ximian.com                            
+ReportedBy: bbjamey at gmail.com               
+QAContact: mono-bugs at ximian.com
+TargetMilestone: ---
+URL: 
+Cc: 
+Summary: Register allocation bug when compiling shift-left operator in very simple loop
+
+Please fill in this template when reporting a bug, unless you know what 
+you are doing.
+Description of Problem:
+
+
+Steps to reproduce the problem:
+1. Take the IL code
+
+
+.class public auto ansi beforefieldinit Foo
+       extends [mscorlib]System.Object
+{
+  .method public static void  _main() cil managed
+  {
+    .entrypoint
+    // Code size       68 (0x44)
+    .maxstack  6
+    .locals init (int32 V_0)
+    IL_0000:  ldc.i4.0
+    IL_0001:  stloc.0
+    IL_0002:  br.s       IL_003b
+
+    IL_0004:  ldstr      "j = {0}"
+    IL_0009:  ldloc.0
+    IL_000a:  box        [mscorlib]System.Int32
+    IL_0014:  call       void [mscorlib]System.Console::WriteLine(string,
+                                                                  object)
+    IL_0019:  ldstr      "res = {0}"
+    IL_001e:  ldc.i4.s   10
+    IL_0020:  ldloc.0
+    IL_0021:  shl
+    IL_0022:  ldc.i4.s   10
+    IL_0024:  ldloc.0
+    IL_0025:  shl
+    IL_0026:  ceq
+    IL_0028:  box        [mscorlib]System.Boolean
+    IL_0032:  call       void [mscorlib]System.Console::WriteLine(string,
+                                                                  object)
+    IL_0037:  ldloc.0
+    IL_0038:  ldc.i4.1
+    IL_0039:  add
+    IL_003a:  stloc.0
+    IL_003b:  ldloc.0
+    IL_003c:  ldc.i4.1
+    IL_003d:  ldc.i4.7
+    IL_003e:  add
+    IL_003f:  blt.s      IL_0004
+
+    IL_0041:  ldnull
+    IL_0042:  pop
+    IL_0043:  ret
+  } // end of method Foo::_main
+
+2. Compile and run using ILASM of the Mono IL assembler.  You will see
+
+j = 0
+res = True
+
+Now run it using .NET 2.0 on Windows.  You should see 
+
+j = 0
+res = True
+j = 1
+res = True
+j = 2
+res = True
+j = 3
+res = True
+j = 4
+res = True
+j = 5
+res = True
+j = 6
+res = True
+j = 7
+res = True
+
+
+Actual Results:
+
+See above
+
+Expected Results:
+
+See above
+
+How often does this happen? 
+
+Always.  The Microsoft C# compiler inserts an "ldc.i4 31 and" in the 
+instruction sequence, which seems to make the bug go away.  However for 
+the range of numbers considered above this should not be a problem.
+
+
+Additional Information:
+
+This code came from the following simple loop when using the F# 
+compiler.  It seems likely to be a fairly catastrophic register 
+allocation error when compiling "<<<".  
+
+    for j = 0 to 7 do 
+      System.Console.WriteLine("j = {0}",j);
+      System.Console.WriteLine("res = {0}",(10 <<< j) = (10 <<< j))
+    done