<html>
    <head>
      <base href="https://bugs.llvm.org/">
    </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 - clang++ rejects legal code"
   href="https://bugs.llvm.org/show_bug.cgi?id=37851">37851</a>
          </td>
        </tr>

        <tr>
          <th>Summary</th>
          <td>clang++ rejects legal code
          </td>
        </tr>

        <tr>
          <th>Product</th>
          <td>clang
          </td>
        </tr>

        <tr>
          <th>Version</th>
          <td>unspecified
          </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>enhancement
          </td>
        </tr>

        <tr>
          <th>Priority</th>
          <td>P
          </td>
        </tr>

        <tr>
          <th>Component</th>
          <td>C++
          </td>
        </tr>

        <tr>
          <th>Assignee</th>
          <td>unassignedclangbugs@nondot.org
          </td>
        </tr>

        <tr>
          <th>Reporter</th>
          <td>zhonghao@pku.org.cn
          </td>
        </tr>

        <tr>
          <th>CC</th>
          <td>dgregor@apple.com, llvm-bugs@lists.llvm.org
          </td>
        </tr></table>
      <p>
        <div>
        <pre>The code is as follow:

#include <iostream>

auto add_1(auto a, auto b) { return a + b;}
auto add_2 = [](auto a, auto b) { return a + b;};

int main()
{
 std::cout
 << "a1: " << add_1(3.5, 4) << "\n"
 << "a2: " << add_1(3, 4.5) << "\n"
 << "a3: " << add_2(3.5, 4) << "\n"
 << "a4: " << add_2(3, 4.5) << "\n";
}

clang++ produces the error messages:
code0.c.cpp:3:12: error: 'auto' not allowed in function prototype
    auto add_1(auto a, auto b) { return a + b;}
code0.c.cpp:3:20: error: 'auto' not allowed in function prototype
    auto add_1(auto a, auto b) { return a + b;}
                       ^~~~
    2 errors generated.

g++ accepts the code. In fact, the code comes from a gcc bug report:

<a href="https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66197">https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66197</a>

The report says that a previous version of gcc compiles the above code into
incorrect binary code, so the above program produces wrong values. It is
interesting to explore whether clang++ has similar problems, right?</pre>
        </div>
      </p>


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