[llvm-bugs] [Bug 30292] New: infinite loop (?) in -simplifycfg

[via llvm-bugs]

https://llvm.org/bugs/show_bug.cgi?id=30292

            Bug ID: 30292
           Summary: infinite loop (?) in -simplifycfg
           Product: new-bugs
           Version: trunk
          Hardware: PC
                OS: Linux
            Status: NEW
          Severity: normal
          Priority: P
         Component: new bugs
          Assignee: unassignedbugs at nondot.org
          Reporter: willdtz at gmail.com
                CC: llvm-bugs at lists.llvm.org
    Classification: Unclassified

Created attachment 17215
  --> https://llvm.org/bugs/attachment.cgi?id=17215&action=edit
bitcode demonstrating bug, from libevent

Encountered this starting about a week ago on trunk, occurred when building
libevent.

With the attached bc file:

$ opt event.bc -simplifycfg -disable-output -debug-pass=Executions
...
[2016-09-06 09:38:06.956737000] 0x3838f10     Executing Pass 'Simplify the CFG'
on Function 'event_base_loop'...


And it proceeds to never complete this pass (hours+).

I'm not sure what the best way to reduce a timing-related bug is, apologies for
the non-reduced test-case.  Even getting this bitcode was more trouble than I
expected (tips welcome, is there a better way?): I ended up using
-print-before=simplifycfg and kludging the function printing pass to dump the
entire module instead.

LMK if you have any questions or problems reproducing on trunk, thanks!

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