[LLVMbugs] [Bug 2806] New: assertion failure in DCE. cpp when executed in debug mode on win32

[bugzilla-daemon at cs.uiuc.edu]

http://llvm.org/bugs/show_bug.cgi?id=2806

           Summary: assertion failure in DCE.cpp when executed in debug mode
                    on win32
           Product: libraries
           Version: trunk
          Platform: PC
        OS/Version: Windows NT
            Status: NEW
          Severity: minor
          Priority: P2
         Component: Scalar Optimizations
        AssignedTo: unassignedbugs at nondot.org
        ReportedBy: asitgoes at gmail.com
                CC: llvmbugs at cs.uiuc.edu


Hi,

  The following code in DCE.cpp(line 113 to 118) causes an assertion failure in
'std::vector' operator--(). 

      for (std::vector<Instruction*>::iterator WI = WorkList.begin();
           WI != WorkList.end(); ++WI)
        if (*WI == I) {
          WI = WorkList.erase(WI);
          --WI;
        }

  When 'WorkList' becomes empty after WorkList.erase, 'WI' will point to the
beginning of the internal buffer of the std::vector. Thus, '--WI' will make
'WI' point to an invalid address. I believe that this will function correctly
since 'WI' will be then incremented by '++WI' of the for loop, however, the
'std::vector' implementation of the visual studio detects that 'WI' will points
to an invalid address after '--' operation, and raises an assertion failure.
  I'd suggest to change this code into 

      for (std::vector<Instruction*>::iterator WI = WorkList.begin();
           WI != WorkList.end(); )
        if (*WI == I) {
          WI = WorkList.erase(WI);
        }
        else {
          ++WI;
        }

  Please let me know if you don't think this need to be fixed. 
  Thanks.


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