[LLVMbugs] [Bug 14968] New: -Wunused-value should not warn about unused constant expanded from a macro

[bugzilla-daemon at llvm.org]

http://llvm.org/bugs/show_bug.cgi?id=14968

             Bug #: 14968
           Summary: -Wunused-value should not warn about unused constant
                    expanded from a macro
           Product: clang
           Version: 3.2
          Platform: PC
        OS/Version: Linux
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: Frontend
        AssignedTo: unassignedclangbugs at nondot.org
        ReportedBy: john at keeping.me.uk
                CC: llvmbugs at cs.uiuc.edu
    Classification: Unclassified


In Git's source code, the following pattern is used to "Let callers be aware of
the constant return value; this can help gcc with -Wuninitialized analysis.":

int foo(int a);
#define foo(a)    (foo(a), 1);

void bar(int a) {
  foo(a);
}

With clang, this causes warnings of the form:

test.c:5:3: warning: expression result unused [-Wunused-value]
  foo(a);
  ^~~~~~
test.c:2:28: note: expanded from macro 'foo'
#define foo(a)    (foo(a), 1);
                           ^

This seems similar to bug 13747, so is this considered to be a bug in clang or
is it a case of "don't do that"?

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