knownConditionTrueFalse - independent smart-pointer and value-flow false positives

[Long Huang]

Repro

Save as value-flow.cpp:

#include <cassert>
#include <memory>

bool DifferentOwners(std::unique_ptr<int>& first, std::unique_ptr<int>& second)
{
   return static_cast<void*>(first.get()) != static_cast<void*>(second.get());
}

double UnknownNumber();

void CompareCopiedValue()
{
   const double number = UnknownNumber();
   const double copy = number;
   assert(!(number <= copy));
   assert(!(number < copy));
   assert(!(number >= copy));
   assert(!(number > copy));
}

class Label
{
public:
   int Height() const;
};

class Overlay
{
public:
   Label* Child();
   void SetText(const char*);
};

void CheckChildResized()
{
   Overlay overlay;
   const Label* label = overlay.Child();
   const int previous = label->Height();
   overlay.SetText("longer");
   assert(label->Height() > previous);
}

Version: Cppcheck 2.22.0 (Linux).

Expected

• unique_ptr::get() returns pointee addresses, not container iterators.
  Comparing two owners' addresses is valid and can establish distinct ownership.
• A copied floating-point value can be NaN. Both number <= copy and
  number >= copy are then false, so they cannot be classified as always true.
  The strict comparisons are intentionally false controls in this example.
• Overlay::SetText can change the child returned by Child(). Calling a
  const getter through a retained child pointer does not freeze its value.

Actual

value-flow.cpp:6: error: Iterators of different containers 'first' and 'second' are used together. [mismatchingContainers]
value-flow.cpp:15: style: The comparison 'number <= copy' is always true because 'number' and 'copy' represent the same value. [knownConditionTrueFalse]
value-flow.cpp:16: style: The comparison 'number < copy' is always false because 'number' and 'copy' represent the same value. [knownConditionTrueFalse]
value-flow.cpp:17: style: The comparison 'number >= copy' is always true because 'number' and 'copy' represent the same value. [knownConditionTrueFalse]
value-flow.cpp:18: style: The comparison 'number > copy' is always false because 'number' and 'copy' represent the same value. [knownConditionTrueFalse]
value-flow.cpp:40: style: The comparison 'label->Height() > previous' is always false because 'label->Height()' and 'previous' represent the same value. [knownConditionTrueFalse]

[CHR]

https://trac.cppcheck.net/ticket/15158 tracks the mismatchingContainersmessage.
Having different smart pointers own the same resource is a bug waiting to happen, so I think showing a warning is desirable.

Other issues still open.

[CHR]

knownConditionTrueFalse is tracked here: https://trac.cppcheck.net/ticket/15171