[LLVMbugs] [Bug 6843] New: analyzer not considering unsignedness of temporary unsigned ints

[bugzilla-daemon at llvm.org]

http://llvm.org/bugs/show_bug.cgi?id=6843

           Summary: analyzer not considering unsignedness of temporary
                    unsigned ints
           Product: clang
           Version: trunk
          Platform: PC
        OS/Version: Linux
            Status: NEW
          Severity: normal
          Priority: P
         Component: Static Analyzer
        AssignedTo: kremenek at apple.com
        ReportedBy: jultay108 at googlemail.com
                CC: llvmbugs at cs.uiuc.edu


when comparing a temporary unsigned integer in a if clause the analyzer does
not consider the unsignedness and checks impossible branches.

testcase:
called with:
scan-build gcc test.c
(svn 101237 debug mode)

#include <stdlib.h>
#include <stdio.h>

unsigned int f(void)
{
  return 2u;
}

int main(void)
{
  int * a = NULL;
  unsigned int count = f();
  // always true even if it overflows
  if ((count + 1u) >= 0u) {
    a = malloc(sizeof(int));
    if (a == NULL)
      return 0;
    *a = 1;
  }
  // analyzer gives NULL dereference warning
  printf("%d\n", *a);
  return 0;
}

it only occurs if the value in the if is a temporary
e.g.
  count = f() + 1u;
  if (count >= 0u) {
correctly handles the the always true if

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