http://llvm.org/bugs/show_bug.cgi?id=21537
Bug ID: 21537
Summary: Clang warnings are inconsistent between compiling from
C source to object code and preprocessed C source to
object code
Product: clang
Version: 3.5
Hardware: PC
OS: Linux
Status: NEW
Severity: normal
Priority: P
Component: Frontend
Assignee: [email protected]
Reporter: [email protected]
CC: [email protected]
Classification: Unclassified
Created attachment 13322
--> http://llvm.org/bugs/attachment.cgi?id=13322&action=edit
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.
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