<html>

    <head>

      <base href="https://llvm.org/bugs/" />

    </head>

    <body><table border="1" cellspacing="0" cellpadding="8">

        <tr>

          <th>Bug ID</th>

          <td><a class="bz_bug_link 

          bz_status_NEW "

   title="NEW --- - A cast<> failed in ExtractLoops()"

   href="https://llvm.org/bugs/show_bug.cgi?id=28783">28783</a>

          </td>

        </tr>

        <tr>

          <th>Summary</th>

          <td>A cast<> failed in ExtractLoops()

          </td>

        </tr>

        <tr>

          <th>Product</th>

          <td>tools

          </td>

        </tr>

        <tr>

          <th>Version</th>

          <td>trunk

          </td>

        </tr>

        <tr>

          <th>Hardware</th>

          <td>PC

          </td>

        </tr>

        <tr>

          <th>OS</th>

          <td>Linux

          </td>

        </tr>

        <tr>

          <th>Status</th>

          <td>NEW

          </td>

        </tr>

        <tr>

          <th>Severity</th>

          <td>normal

          </td>

        </tr>

        <tr>

          <th>Priority</th>

          <td>P

          </td>

        </tr>

        <tr>

          <th>Component</th>

          <td>bugpoint

          </td>

        </tr>

        <tr>

          <th>Assignee</th>

          <td>unassignedbugs@nondot.org

          </td>

        </tr>

        <tr>

          <th>Reporter</th>

          <td>feishenniubi@gmail.com

          </td>

        </tr>

        <tr>

          <th>CC</th>

          <td>llvm-bugs@lists.llvm.org

          </td>

        </tr>

        <tr>

          <th>Classification</th>

          <td>Unclassified

          </td>

        </tr></table>

      <p>

        <div>

        <pre>Created <span class=""><a href="attachment.cgi?id=16845" name="attach_16845" title="The input .ll file that triggered the bug">attachment 16845</a> <a href="attachment.cgi?id=16845&action=edit" title="The input .ll file that triggered the bug">[details]</a></span>

The input .ll file that triggered the bug

I tried to use bugpoint to help me pinpoint a miscompilation bug in loop

optimizers, yet bugpoint itself crashes when trying to extract loops from the

miscompiled function.

The source of the error can be narrowed down to the ExtractLoops() function

inside Miscompilation.cpp. Around line 339 there's a statement

"MiscompiledFunctions[i] = cast<Function>(VMap[MiscompiledFunctions[i]]);". The

right-hand-side of this statement, i.e. VMap[...], turns out to be an empty

WeakVH rather than a Function*. 

This is how I invoked bugpoint: 

<span class="quote">> bugpoint -run-llc -safe-run-llc test.ll -loop-unroll -gcc=clang++</span >

This is what I got back from the invocation:

Read input file      : 'test.ll'

*** All input ok

Running selected passes on program to test for crash: Success!

Initializing execution environment: Found llc:

/home/grieve/LLVM/GSoC/Testing/debugBuild/bin/llc

Running the code generator to test for a crash: <llc>

Generating reference output from raw program: <llc><llc><CC><program>

Reference output is: bugpoint.reference.out-17cf006

*** Checking the code generator...

<llc><CC><program>

*** Output matches: Debugging miscompilation!

Checking to see if '' compiles correctly: <llc><CC><program> yup.

Checking to see if '-loop-unroll' compiles correctly: <llc><CC><program> nope.

*** Found miscompiling pass: -loop-unroll

Emitted bitcode to 'bugpoint-passinput.bc'

*** You can reproduce the problem with: opt bugpoint-passinput.bc -loop-unroll

Checking to see if the program is misoptimized when these functions are run

through the pass: main _ZNSt5dequeIdSaIdEE18_M_fill_initializeERKd

_ZNSt11_Deque_baseIdSaIdEE17_M_initialize_mapEm

_ZNSt11_Deque_baseIdSaIdEE15_M_create_nodesEPPdS3_ __clang_call_terminate