[llvm-bugs] [Bug 33701] New: LoopRotation's DomTree update logic doesn't handle nodes with no predecessors

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=33701

            Bug ID: 33701
           Summary: LoopRotation's DomTree update logic doesn't handle
                    nodes with no predecessors
           Product: new-bugs
           Version: trunk
          Hardware: PC
                OS: Linux
            Status: NEW
          Severity: normal
          Priority: P
         Component: new bugs
          Assignee: unassignedbugs at nondot.org
          Reporter: kubakuderski at gmail.com
                CC: llvm-bugs at lists.llvm.org

Created attachment 18760
  --> https://bugs.llvm.org/attachment.cgi?id=18760&action=edit
reduced repro

LoopRotation::rotateLoop tries to manually update DomTree by iterating over all
predecessors of some basic block and computing NearestCommonDominator.

Is there's a predecessor that is unreachable, rotateLoop uses nullptr as a new
IDom for the blocks, which results in a crash.


===============================================

opt -S -loop-rotate -o - reduced9.ll

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