[llvm-bugs] [Bug 27065] New: BasicBlock::removePredecessor generates self-referencing instructions

[via llvm-bugs]

https://llvm.org/bugs/show_bug.cgi?id=27065

            Bug ID: 27065
           Summary: BasicBlock::removePredecessor generates
                    self-referencing instructions
           Product: libraries
           Version: trunk
          Hardware: PC
                OS: Linux
            Status: NEW
          Severity: normal
          Priority: P
         Component: Transformation Utilities
          Assignee: unassignedbugs at nondot.org
          Reporter: tobias at grosser.es
                CC: llvm-bugs at lists.llvm.org
    Classification: Unclassified

Created attachment 16088
  --> https://llvm.org/bugs/attachment.cgi?id=16088&action=edit
Infinitely running test case

BasicBlock::removePredecessor will eliminate PHI nodes entirely if they always
evaluate to a single constant value and instead replace all uses of the PHINode
with this constant.

This is only correct if we know that the actual constant actually dominates the
PHI node, which is not verified in this code. As a result, we may generate self
referencing instructions which is not only incorrect but also causes an
infinite loop in -load-combine, which does not expect such IR.

This command does not terminate for me, as jump-treading uses removePredecessor
and introduces the incorrect IR that load-combine can not handle:

opt /tmp/infinite.ll -jump-threading -load-combine

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