[LLVMbugs] [Bug 21335] New: False positive scoping issues, deref pointer, dead init, uninit arg, val, etc.

[bugzilla-daemon at llvm.org]

http://llvm.org/bugs/show_bug.cgi?id=21335

            Bug ID: 21335
           Summary: False positive scoping issues, deref pointer, dead
                    init, uninit arg, val, etc.
           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

Could be related to active bugs, e.g. 11722? 

The main case, simple (suspected)related repro follows:

Scan-build flagged the following in std::<locale>
libcxx/include/locale:3240:21: warning: Dereference of null pointer
            *__nc++ = '-';
            ~~~~~~~~^~~~~
Code looks like this:
   if (__wn - __wb.get() > __bz-2)
        {
            __h.reset((char*)malloc(static_cast<size_t>(__wn - __wb.get() +
2)));
            if (__h.get() == 0)
                __throw_bad_alloc();
            __nc = __h.get();
        }
        if (__neg)
            *__nc++ = '-';

I changed the code and rebuilt the lib like this and still got the warning
//after __h.reset...
__nc = __h.get();
if(__nc == nullptr)
  throw..

Here is a stand-alone repro.  I do not get the deref issue, but it does seem to
get thrown off by the if blocks

#include <exception>
#include <cstdlib>
#include <iostream>

int main() {

  std::unique_ptr<char, void(*)(void*)> sp(0, std::free);
  char buf[100];
  char * p = buf;

  if(true) {
   sp.reset((char*)malloc(static_cast<size_t>(99)));
   p = sp.get();
   if(p == nullptr)
      throw std::bad_alloc();
  }
  if(true)
     *p++ = '-';

   std::cout << *p;
}

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