[llvm-bugs] [Bug 45835] New: IndVars creates an invalid phi node after r367485

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=45835

            Bug ID: 45835
           Summary: IndVars creates an invalid phi node after r367485
           Product: libraries
           Version: trunk
          Hardware: PC
                OS: Windows NT
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: Scalar Optimizations
          Assignee: unassignedbugs at nondot.org
          Reporter: dmajor at mozilla.com
                CC: efriedma at quicinc.com, florian_hahn at apple.com,
                    froydnj at gmail.com, listmail at philipreames.com,
                    llvm-bugs at lists.llvm.org
            Blocks: 45309

https://godbolt.org/z/Me95yj

After r367485/llvmorg-10-init-991-gf8e7b536571, this phi node:
  %a.mux.lcssa4 = phi i8* [ %a.mux, %switch.early.test.i ], [ %a.mux,
%switch.early.test.i ], [ %a.mux, %cond.end ]

becomes
  %a.mux.lcssa4 = phi i8* [ %a.mux, %switch.early.test.i ], [ %scevgep,
%switch.early.test.i ], [ %scevgep, %cond.end ]

which has two different values for %switch.early.test.i.

This started out as an investigation of a clang hang in LICM (full repro
available on request) but this phi node is the first place that the verifier
started complaining, so I assume the rest is GIGO from there.

The bad phi is no longer seen after llvmorg-11-init-4213-gd6f47aeb519, but as
that is a cost model patch, I assume it's not really a fix but just an
avoidance.


Referenced Bugs:

https://bugs.llvm.org/show_bug.cgi?id=45309
[Bug 45309] [meta] 10.0.1 Release Blockers
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