[LLVMbugs] [Bug 2232] New: empty MBB results in incorrect MBB2IdxMap and Idx2MBBMap

[bugzilla-daemon at cs.uiuc.edu]

http://llvm.org/bugs/show_bug.cgi?id=2232

           Summary: empty MBB results in incorrect MBB2IdxMap and Idx2MBBMap
           Product: new-bugs
           Version: unspecified
          Platform: PC
        OS/Version: Windows NT
            Status: NEW
          Severity: normal
          Priority: P2
         Component: new bugs
        AssignedTo: unassignedbugs at nondot.org
        ReportedBy: scott.llvm at h4ck3r.net
                CC: llvmbugs at cs.uiuc.edu


In the LiveIntervalAnalysis::runOnMachineFunction, there is a code to
compute the MBB2IdxMap and Idx2MBBMap, by remembering for each MBB its start
and end instruction numbers.

If an MBB is empty, the end index will be larger than the start in MBB2IdxMap,
and multiple entries of .first Idx2MBBMap will identical. On some platforms
this causes an assert later (in e.g. LiveIntervals::findLiveinMBBs
std::lower_bound), and possibly incorrect search behaviour.


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