<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-cl] Don't emit dllexport inline function definitions from pch files"
   href="https://bugs.llvm.org/show_bug.cgi?id=37801">37801</a>
          </td>
        </tr>

        <tr>
          <th>Summary</th>
          <td>[clang-cl] Don't emit dllexport inline function definitions from pch files
          </td>
        </tr>

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

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

        <tr>
          <th>Component</th>
          <td>-New Bugs
          </td>
        </tr>

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

        <tr>
          <th>Reporter</th>
          <td>hans@chromium.org
          </td>
        </tr>

        <tr>
          <th>CC</th>
          <td>llvm-bugs@lists.llvm.org
          </td>
        </tr></table>
      <p>
        <div>
        <pre>The definitions will already be present in the .obj file generated when
building the PCH. Not emitting them again saves a lot of compile time.

For example,


header.h

  #ifndef HEADER_H
  #define HEADER_H

  inline int __declspec(dllexport) foo() {
    return 42;
  }

  #endif


precompiled_header.h

  #include "header.h"


precompiled_header.cc

  // No include needed; the include is forced with /FI.


a.cc

  #include "header.h"

  int __declspec(dllexport) bar() {
    return 1;
  }


To build the PCH file:

  cl /c precompiled_header.cc /FIprecompiled_header.h /Ycprecompiled_header.h
/Fppch.pch


Note how the definition of foo() is emitted into precompiled_header.obj:

  dumpbin /directives precompiled_header.obj | grep EXPORT
     /EXPORT:?foo@@YAHXZ


To use the PCH when compiling a.cc:

  cl /c a.cc /FIprecompiled_header.h /Yuprecompiled_header.h /Fppch.pch


Note how the definition of foo() is *not* emitted into a.obj:

  dumpbin /directives a.obj | grep EXPORT
     /EXPORT:?bar@@YAHXZ


If we had not used the PCH, foo() would have been emitted:

  cl /c a.cc && dumpbin /directives a.obj | grep EXPORT
     /EXPORT:?foo@@YAHXZ
     /EXPORT:?bar@@YAHXZ


clang-cl does not do this optimization, and always emits foo() even if it came
from the PCH.</pre>
        </div>
      </p>


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