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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW --- - Clang warnings are inconsistent between compiling from C source to object code and preprocessed C source to object code"
href="http://llvm.org/bugs/show_bug.cgi?id=21537">21537</a>
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<th>Summary</th>
<td>Clang warnings are inconsistent between compiling from C source to object code and preprocessed C source to object code
</td>
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<th>Product</th>
<td>clang
</td>
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<th>Version</th>
<td>3.5
</td>
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<th>Hardware</th>
<td>PC
</td>
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<th>OS</th>
<td>Linux
</td>
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<th>Status</th>
<td>NEW
</td>
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<th>Severity</th>
<td>normal
</td>
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<th>Priority</th>
<td>P
</td>
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<th>Component</th>
<td>Frontend
</td>
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<th>Assignee</th>
<td>unassignedclangbugs@nondot.org
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<th>Reporter</th>
<td>jonathan.hamilton@imgtec.com
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<th>CC</th>
<td>llvmbugs@cs.uiuc.edu
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<th>Classification</th>
<td>Unclassified
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<p>
<div>
<pre>Created <span class=""><a href="attachment.cgi?id=13322" name="attach_13322" title="C test code having a tautological comparison as the result of a preprocessor macro expansion.">attachment 13322</a> <a href="attachment.cgi?id=13322&action=edit" title="C test code having a tautological comparison as the result of a preprocessor macro expansion.">[details]</a></span>
C test code having a tautological comparison as the result of a preprocessor
macro expansion.
Clang appears to handle some symbols differently with respect to warnings
depending on if the code is the result of a preprocessor macro expansion or
not.
This causes an inconsistency between pre-processing and compiling a source file
in one step to preprocessing then compiling as two stages.
For example, using the attached test program building (with clang 3.5.0 on
x86_64) with the following command line:
clang -Werror tautological-compare-in-macro.c -o /dev/null -c
succeeds with no warnings/errors. However running:
clang -Werror tautological-compare-in-macro.c -o
tautological-compare-in-macro.p -E
clang -Werror -x c tautological-compare-in-macro.p -o /dev/null -c
causes it to emit a warning (-Wtautological-compare, which causes this to fail
due to -Werror)
This is rather annoying when large projects add -Werror to their build systems.
This example was specifically seen (and significantly simplified from) a file
in Android.</pre>
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