<table border="1" cellspacing="0" cellpadding="8">
    <tr>
        <th>Issue</th>
        <td>
            <a href=https://github.com/llvm/llvm-project/issues/61173>61173</a>
        </td>
    </tr>

    <tr>
        <th>Summary</th>
        <td>
            Incorrect code generation in conjunction with linker scripts
        </td>
    </tr>

    <tr>
      <th>Labels</th>
      <td>
      </td>
    </tr>

    <tr>
      <th>Assignees</th>
      <td>
      </td>
    </tr>

    <tr>
      <th>Reporter</th>
      <td>
          rgrr
      </td>
    </tr>
</table>

<pre>
    Summary
---

It seems that the optimizer does not consider symbols created during link time under certain circumstances.

The problem appeared first in a project during link time optimization.  Digging deeper with the test program showed that the problem must be caused by the optimizer.

Linker scripts are part of the problem.


About the test program
---
Test program: https://github.com/rgrr/playground/tree/feature/llvm-games/llvm-games/broken-lto

The code has been taken more or less from a real life example but very much stripped down: in the Nordic SDK observers can be defined in the application for certain events.  The number of observers is not limited.

Pointers/parameters to the observers are collected in special link section. The linker (script) generates `__start` / `__stop` symbols for each segments and a function `sdh_observer_notify()` iterates over those sections calling the defined observers.  Empty sections (i.e. no observer defined) are pretty legal.

In the test program there are two types of observers: `stack_observer` and `soc_observer` (names are actually irrelevant).  There are four `stack_observer` and no `soc_observer` (except in a special testcase). In the test program the observers are doing simple output to stdout.

The program runs successful with '-O0' and fails with '-O1'.  Debugging shows that '-O1' has altered the loop in TMO illegal way: the for-loop seems to be transformed into a do-while-loop.  So an empty list of observers leads to a crash.

Testing
---
1.  `make test-O0-ok` - compiles with '-O0' and sends some output to the terminal
1. `make test-O1-fail` - compiles with '-O1' and crashes on output of the empty `soc_observer`
1. `make test-O1-ok-with-observer` - compiles with '-O1' successfully to show that the problem is with an empty list
1. `make test-O0-fail-compile-error` - compiles with '-O0' and generates a compile time error I actually do not understand (different story)
1. `make test-O1-fail-with-inline-iter-get` - compiles with '-O1' and fails during runtime.  Just to show, that compilation succeeds.

**(2.) is the actual problem where wrong code is generated.**

Environment
---
I have tested on Debian with clang 15.0.7.  lld-15 has to be installed as well.

</pre>
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