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<base href="https://llvm.org/bugs/" />
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<body><table border="1" cellspacing="0" cellpadding="8">
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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW --- - undef doesn't work well with pch files"
href="https://llvm.org/bugs/show_bug.cgi?id=31311">31311</a>
</td>
</tr>
<tr>
<th>Summary</th>
<td>undef doesn't work well with pch files
</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>All
</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>Frontend
</td>
</tr>
<tr>
<th>Assignee</th>
<td>unassignedclangbugs@nondot.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>nicolasweber@gmx.de
</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>$ cat foo2.h
#undef ARG
$ cat foo2.c
const int i = ARG;
$ ./bin/clang -cc1 -DARG -include foo2.h foo2.c -emit-obj -o a.o
foo2.c:1:15: error: use of undeclared identifier 'ARG'
const int i = ARG;
^
1 error generated.
$ ./bin/clang -cc1 -emit-pch -o foo2.h.pch foo2.h
$ ./bin/clang -cc1 -DARG -include-pch foo2.h.pch foo2.c -emit-obj -o a.o
This should err when going through a pch as well.
Similar but slightly more difficult to fix: The same with a builtin macro:
$ cat foo2.h
#undef __FILE__
$ cat foo2.c
const char s[] = __FILE__;
s$ bin/clang -cc1 -include foo2.h foo2.c -emit-obj -o a.o
In file included from <built-in>:1:
./foo2.h:1:8: warning: undefining builtin macro
#undef __FILE__
^
foo2.c:1:18: error: use of undeclared identifier '__FILE__'
const char s[] = __FILE__;
^
1 warning and 1 error generated.
$ ./bin/clang -cc1 -emit-pch -o foo2.h.pch foo2.h
foo2.h:1:8: warning: undefining builtin macro
#undef __FILE__
^
1 warning generated.
$ ./bin/clang -cc1 -include-pch foo2.h.pch foo2.c -emit-obj -o a.o
This too should error out but doesn't.
Problems, partial list:
1. shouldIgnoreMacro() in ASTWriter.cpp stops at isBuiltinMacro(), but that's
true for undefs of builtin macros as well. It probably should have `if
(MD->getKind() != MacroDirective::MD_Define) return false;` as its first line.
2. ASTWriter only writes out identifiers with a ref (see AddIdentifierRef).
ASTWriter::WritePreprocessor() only calls this for macros with a MacroInfo, and
macros that are only #undef'd but never defined (at pch creation time) get
dropped.
3. It seems that pch files get loaded before commandline -D flags are
processed, and Preprocessor::HandleUndefDirective() ignores undefs for macros
without a MacroInfo (which makes sense) (not really sure if the ordering here
is like I say, but if it weren't then `#define FOO` in the .h and -DFOO on the
command passing -include-pch would behave differently)
(Spin-off from <a class="bz_bug_link
bz_status_NEW "
title="NEW --- - Redefining __DATE__ or __TIME__ with pch causes Assertion failed: (!StoredMD.getLatest() && "the macro history was modified before initializing it from a pch")"
href="show_bug.cgi?id=29119">bug 29119</a>)</pre>
</div>
</p>
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