[LLVMbugs] [Bug 774] NEW: SwitchInst default block doesn't get optimized away

[bugzilla-daemon at cs.uiuc.edu]

http://llvm.org/bugs/show_bug.cgi?id=774

           Summary: SwitchInst default block doesn't get optimized away
           Product: libraries
           Version: trunk
          Platform: PC
        OS/Version: Linux
            Status: NEW
          Severity: normal
          Priority: P2
         Component: Scalar Optimizations
        AssignedTo: unassignedbugs at nondot.org
        ReportedBy: nicholas at mxc.ca


LLVM doesn't seem to do a good job of removing the default block of a switch
statement. Given the C++ code:

  int test1(bool b)
  {
    switch (b) {
      case true:
        return 1;
      case false:
        return 2;
      default:
        return 3;
    }
    return 4;
  }

The return 4 is removed, but return 3 is kept. By contrast, the same logic with
if statements:

  int test1if(bool b)
  {
    if (b == true)
      return 1;
    else if (b == false)
      return 2;
    else
      return 3;
  
    return 4;
  }

becomes:

  int %_Z7test1ifb(bool %b) {
  entry:
          %retval = select bool %b, int 1, int 2          ; <int> [#uses=1]
          ret int %retval
  }

so it's clear that LLVM should know what's going on.



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