[LLVMbugs] [Bug 10211] New: False positives with -Wconstant-logical-operand in template code

bugzilla-daemon at llvm.org bugzilla-daemon at llvm.org
Mon Jun 27 19:27:17 PDT 2011


           Summary: False positives with -Wconstant-logical-operand in
                    template code
           Product: clang
           Version: trunk
          Platform: PC
        OS/Version: All
            Status: NEW
          Severity: normal
          Priority: P
         Component: C++
        AssignedTo: unassignedclangbugs at nondot.org
        ReportedBy: rjmccall at apple.com
                CC: llvmbugs at cs.uiuc.edu, dgregor at apple.com

-Wconstant-logical-operand warns about code where the constant argument was
instantiated from a template.  This is idiomatically acceptable code.  It comes
up a lot in e.g. Eigen:
Anyone verifying this should probably do a test compile with some Eigen files,
e.g. 2.0.15's test/geometry.cpp [note: clang -I.. -D test_geometry], but here's
a short reduction of a few cases we should get:

  template <class T> class A {
    unsigned count() { return 0; }

    bool test1() { return (count() && int(T::SomeBit)); }

    enum {
      SomeBit = T::SomeBit
    bool test2() { return (count() && int(SomeBit)); }
  struct B { enum { SomeBit = true }; };
  template class A<B>;

The warning doesn't trigger here without the function-style casts.

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