[llvm-bugs] [Bug 27693] New: phi node arguments oscillate with passes loop-rotate and simplifycfg

[via llvm-bugs]

https://llvm.org/bugs/show_bug.cgi?id=27693

            Bug ID: 27693
           Summary: phi node arguments oscillate with passes loop-rotate
                    and simplifycfg
           Product: libraries
           Version: trunk
          Hardware: PC
                OS: Linux
            Status: NEW
          Severity: normal
          Priority: P
         Component: Scalar Optimizations
          Assignee: unassignedbugs at nondot.org
          Reporter: nwilson20 at gmail.com
                CC: llvm-bugs at lists.llvm.org
    Classification: Unclassified

Created attachment 16342
  --> https://llvm.org/bugs/attachment.cgi?id=16342&action=edit
loop-rotate_simplifycfg.ll

When using the flags -loop-rotate and -simplifycfg on the attached IR
(loop-rotate_simplifycfg.ll) the phi node arguments will keep flipping. This
was produced by using the attached IR and using the output as input back to
opt.

For example:
$ ./opt -S -loop-rotate -simplifycfg loop-rotate_simplifycfg.ll > out1.ll
$ ./opt -S -loop-rotate -simplifycfg out1.ll > out2.ll
$ ./opt -S -loop-rotate -simplifycfg out2.ll > out3.ll

$ diff out1.ll loop-rotate_simplifycfg.ll
1c1
< ; ModuleID = 'loop-rotate_simplifycfg.ll'
---
> ; ModuleID = 'bugpoint-reduced-simplified.bc'
23,24c23,24
< while.cond:                                       ; preds = %cond.true.i57,
%entry, %while.cond
<   %1 = phi %class.CBlockIndex.16.242.1142* [ null, %while.cond ], [ null,
%entry ], [ %0, %cond.true.i57 ]
---
> while.cond:                                       ; preds = %while.cond, %cond.true.i57, %entry
>   %1 = phi %class.CBlockIndex.16.242.1142* [ %0, %cond.true.i57 ], [ null, %entry ], [ null, %while.cond ]



$ diff out2.ll out1.ll
1c1
< ; ModuleID = 'out1.ll'
---
> ; ModuleID = 'loop-rotate_simplifycfg.ll'
24c24
<   %1 = phi %class.CBlockIndex.16.242.1142* [ null, %while.cond ], [ %0,
%cond.true.i57 ], [ null, %entry ]
---
>   %1 = phi %class.CBlockIndex.16.242.1142* [ null, %while.cond ], [ null, %entry ], [ %0, %cond.true.i57 ]



$ diff out3.ll out2.ll
1c1
< ; ModuleID = 'out2.ll'
---
> ; ModuleID = 'out1.ll'
24c24
<   %1 = phi %class.CBlockIndex.16.242.1142* [ null, %while.cond ], [ null,
%entry ], [ %0, %cond.true.i57 ]
---
>   %1 = phi %class.CBlockIndex.16.242.1142* [ null, %while.cond ], [ %0, %cond.true.i57 ], [ null, %entry ]

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