Invalid "Warning: Unreachable code detected" on STOP RUN statement

[alvaro-vantis-pt]

Describe the bug Message of Unreachable code when code is on normal program flow. Using TypeCobol V1.5.11.

To Reproduce run TypeCobol.CLI.exe with "-cfg=2" or "-cfg=3" option. The error does not occurs when -cfg=1 is in effect.

Expected behavior "Warning: Unreachable code detected" should be shown only for unreachable code lines

Example of Code to reproduce the problem:

       IDENTIFICATION DIVISION.
       PROGRAM-ID. TESTP02.
       PROCEDURE DIVISION.
       MAIN-SECTION SECTION.
           PERFORM SECTION1
                  STOP RUN.

       SECTION1 SECTION.
           DISPLAY "SECTION1".
           GO TO SECTION2.
           DISPLAY "UNREACHABLE CODE".
           PERFORM SECTION3.
       A01-EXIT.
           EXIT.

       SECTION2 SECTION.
           DISPLAY "SECTION2".
           GOBACK.

       SECTION3 SECTION.
           DISPLAY "SECTION3".

       SECTION4 SECTION.
           DISPLAY "SECTION4".
           GOBACK.
       END PROGRAM TESTP02.

Test runs:

TypeCobol.CLI.exe -cfg=2 -i=c:StopRunSection1 -o=c:out.cbl 2/28/2022 3:05:03 PM start parsing of StopRunSection1

ReturnCode=Warning_ 9 errors in "c:StopRunSection1": Line 6[19,22] <37, Warning, General> - Warning: GOBACK should be used instead of STOP RUN Line 6[19,26] <37, Warning, General> - Warning: Unreachable code detected Line 11[12,37] <37, Warning, General> - Warning: Unreachable code detected Line 12[12,27] <37, Warning, General> - Warning: Unreachable code detected Line 14[12,15] <37, Warning, General> - Warning: Unreachable code detected Line 21[12,29] <37, Warning, General> - Warning: Unreachable code detected Line 24[12,29] <37, Warning, General> - Warning: Unreachable code detected Line 25[12,17] <37, Warning, General> - Warning: Unreachable code detected Line 5[12,27] <37, Warning, General> - Warning: Statement ' GO TO SECTION2' located at line 10, column 12 prevents this PERFORM statement to reach its exit. parsed in 00:00:01.1221179 ms

Code: 1 TypeCobol.CLI.exe: Operation failed Try TypeCobol.CLI.exe --help for usage information.

TypeCobol.CLI.exe -cfg=3 -i=c:StopRunSection1 -o=c:out.cbl 2/28/2022 3:05:10 PM start parsing of StopRunSection1

ReturnCode=Warning_ 9 errors in "c:StopRunSection1": Line 6[19,22] <37, Warning, General> - Warning: GOBACK should be used instead of STOP RUN Line 6[19,26] <37, Warning, General> - Warning: Unreachable code detected Line 11[12,37] <37, Warning, General> - Warning: Unreachable code detected Line 12[12,27] <37, Warning, General> - Warning: Unreachable code detected Line 14[12,15] <37, Warning, General> - Warning: Unreachable code detected Line 21[12,29] <37, Warning, General> - Warning: Unreachable code detected Line 24[12,29] <37, Warning, General> - Warning: Unreachable code detected Line 25[12,17] <37, Warning, General> - Warning: Unreachable code detected Line 5[12,27] <37, Warning, General> - Warning: Statement ' GO TO SECTION2' located at line 10, column 12 prevents this PERFORM statement to reach its exit. parsed in 00:00:01.0822997 ms

Code: 1 TypeCobol.CLI.exe: Operation failed Try TypeCobol.CLI.exe --help for usage information.

TypeCobol.CLI.exe -cfg=1 -i=c:StopRunSection1 -o=c:out.cbl 2/28/2022 3:05:18 PM start parsing of StopRunSection1

ReturnCode=Warning_ 8 errors in "c:StopRunSection1": Line 6[19,22] <37, Warning, General> - Warning: GOBACK should be used instead of STOP RUN Line 11[12,37] <37, Warning, General> - Warning: Unreachable code detected Line 12[12,27] <37, Warning, General> - Warning: Unreachable code detected Line 14[12,15] <37, Warning, General> - Warning: Unreachable code detected Line 21[12,29] <37, Warning, General> - Warning: Unreachable code detected Line 24[12,29] <37, Warning, General> - Warning: Unreachable code detected Line 25[12,17] <37, Warning, General> - Warning: Unreachable code detected Line 5[12,27] <37, Warning, General> - Warning: Statement ' GO TO SECTION2' located at line 10, column 12 prevents this PERFORM statement to reach its exit. parsed in 00:00:01.0912782 ms

Code: 1 TypeCobol.CLI.exe: Operation failed Try TypeCobol.CLI.exe --help for usage information.

[smedilol]

Hello,

Thanks for the feedback. We are currently focusing on fixing blocking bug with our parser for our Cobol developers. Maybe we'll work on this kind of issues in a few weeks.

[alvaro-vantis-pt]

Thanks for the feedback. It seems that the problem is not related to "STOP RUN" statement, but the fact that it is after a PERFORM paragraph statement, because: 1) The same thing happened with another program with ALTER statement that is after a PERFORM paragraph statement; 2) Debugging it with visual studio, I found that the problem seems to be on the following function on ControlFlowGraphBuilder.cs:

    /// <summary>
    /// Extend BasicBlockForNodeGroup instance to point to the first block and make all terminal blocks
    /// have for successor the block successor.
    /// </summary>
    /// <param name="group">The group to be continued</param>
    private void ContinueBasicBlockGroup(BasicBlockForNodeGroup group)
    {
        if (group.Group.Count > 0)
        {
            System.Diagnostics.Debug.Assert(group.SuccessorEdges.Count == 1);
            int succIndex = group.SuccessorEdges[0];
            group.SuccessorEdges.Clear();

            //Make the First block the successor of the group
            LinkedListNode<BasicBlock<Node, D>> first = group.Group.First;
            int firstIndex = this.CurrentProgramCfgBuilder.Cfg.SuccessorEdges.Count;
            group.SuccessorEdges.Add(firstIndex);
            this.CurrentProgramCfgBuilder.Cfg.SuccessorEdges.Add(first.Value);

            //Make all terminal blocks of the group have the original successor of the block.
            foreach (var termBlock in group.TerminalBlocks)
            {
                if (!termBlock.SuccessorEdges.Contains(succIndex))
                {
                    if (!termBlock.HasFlag(BasicBlock<Node, D>.Flags.Ending))
                    {
                        termBlock.SuccessorEdges.Add(succIndex);
                    }
                }
            }
            group.SetFlag(BasicBlock<Node, D>.Flags.GroupGrafted, true);
        }
    }

When running with cfg 3, it enters 3 times on this function. The variable group.SuccessorEdges[0] has the correct value before the executation of "group.SuccessorEdges.Clear();" and gets a wrong value on "termBlock.SuccessorEdges.Add(succIndex);"