FP: unsignedLessThanZero from known false constexpr if

[Lionel Gimbert]

Hello,

I encounter a case where cppcheck complain about a unsignedLessThanZero in a bit of code that is (for this case) in the code block of a constexpr false if:

  uint32_t u32 = 4096u;
  if constexpr (std::numeric_limits<uint32_t>::is_signed) // same result with if constexpr (false)
  {
    if(u32 < 0) {} //FP: Checking if unsigned expression 'u32' is less than zero. [unsignedLessThanZero]
  }

(real code is templated and the type can be signed).

While it is true that, out of context, u32 < 0 should return this issue, I would expect if constexpr (false) {} to behave like #if 0 \ #endif and don't have this bit of code analyzed.

I made this topic about unsignedLessThanZero but it is probably a wider issue of handling constexpr.
I see this issue with both 2.10, 2.13.2 and current head of main (bef9e73e60a61a382f4341cfb70730ea67948132).

[CHR]

Thanks for reporting, ticket is here: https://trac.cppcheck.net/ticket/12387