[LLVMbugs] [Bug 21333] New: false positive smartptr release (unique_ptr) in std::<memory>

bugzilla-daemon at llvm.org bugzilla-daemon at llvm.org
Tue Oct 21 16:55:49 PDT 2014


            Bug ID: 21333
           Summary: false positive smartptr release (unique_ptr) in
           Product: clang
           Version: unspecified
          Hardware: PC
                OS: Linux
            Status: NEW
          Severity: normal
          Priority: P
         Component: Static Analyzer
          Assignee: kremenek at apple.com
          Reporter: stevemac321 at live.com
                CC: llvmbugs at cs.uiuc.edu
    Classification: Unclassified

Not sure anything can be done about this.  If there exists guidance for what
constitutes a false positive, it would be great if someone could point it to
me.  I am running scan-build against libc++ and do not want to spam the bug

Anyway, scan-build flags this:

libcxx/include/memory:2622:9: warning: Use of memory after it is freed
        return __t;

The code looks like this:
        pointer __t = __ptr_.first();
        __ptr_.first() = pointer();
        return __t;
It is a reasonable pattern, MSVC STL does basically the same thing.  The
standard says this:  N3797  [unique.ptr.single.modifiers]

pointer release() noexcept;
1 Postcondition: get() == nullptr.
2 Returns: The value get() had at the start of the call to release.

My env:
clang version 3.6.0 (trunk 217475)
Target: x86_64-unknown-linux-gnu
Thread model: posix

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