[llvm-bugs] [Bug 31322] New: crash in FlattenCFG: MergeIfRegion

[via llvm-bugs]

https://llvm.org/bugs/show_bug.cgi?id=31322

            Bug ID: 31322
           Summary: crash in FlattenCFG: MergeIfRegion
           Product: libraries
           Version: trunk
          Hardware: PC
                OS: Windows NT
            Status: NEW
          Severity: normal
          Priority: P
         Component: Backend: AMDGPU
          Assignee: unassignedbugs at nondot.org
          Reporter: pichet2000 at gmail.com
                CC: llvm-bugs at lists.llvm.org
    Classification: Unclassified

Created attachment 17742
  --> https://llvm.org/bugs/attachment.cgi?id=17742&action=edit
reduced test case

FlattenCFG seem to be used only by AMDGPU.
I found this bug by using FlattenCFG pass for another out of tree target but I
can reproduce it with AMDGPU too.


Seem like MergeIfRegion is removing a BB still referenced by a PHI node.

reduction in test.ll 

opt -flattencfg -disable-output test.ll

opt will crash

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