Checked region finder doesn't consider all casts inserted by CastPlacementVisitor

[john-h-kastner]

If the argument to a function is a literal expression that does not have an associated ConstraintVariable, then CheckedRegionFinder will make the containing function _Checked even if the function call requires a cast.

For expression with constraint variables, a function call can only require a cast if either the parameter constraint variable or the argument constraint variable is wild. If the argument does not get any constraint variables, for example in the case of an integer literal, but a cast is still required, then the checked region finder considers the code safe and will add a checked region.

void foo(char *a){}
void bar() {
  foo(1);
}

will convert to

void foo(_Ptr<char> a)_Checked {}

void bar() _Checked {
  foo(_Assume_bounds_cast<_Ptr<char>>(1));
}

[mwhicks1]

Right: In general the presence of a _Assume_bounds_cast means that the region cannot be checked. Note that turning on -addcr for the example in #524 also incorrectly adds _Checked to foo.