[LLVMbugs] [Bug 18299] New: False positive when aliasing structure

[bugzilla-daemon at llvm.org]

http://llvm.org/bugs/show_bug.cgi?id=18299

            Bug ID: 18299
           Summary: False positive when aliasing structure
           Product: clang
           Version: unspecified
          Hardware: Macintosh
                OS: MacOS X
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: Static Analyzer
          Assignee: kremenek at apple.com
          Reporter: carl at lytro.com
                CC: llvmbugs at cs.uiuc.edu
    Classification: Unclassified

I've attached a complete test case, but the simple breakdown is that this
function:

int f(void)
{
    struct { int i; } s = { 0 };
    char *c = (char *)&s;

    return c[1];
}

Yields a static analysis warning saying:

example.c:6:5: warning: Undefined or garbage value returned to caller
    return c[1];
    ^~~~~~~~~~~
1 warning generated.

Which, as far as I know, it shouldn't.  Changing 'struct' to 'union' doesn't
give the warning, nor does removing the struct entirely and just using 'int i'
directly.

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