No signed integer overflow warning reported in the call to constructor

[Fedr]

In the following program there are two similar signed integer overflows:

#include <cstdint>

void func(uint64_t) {}

struct A { 
    A(uint64_t){} 
};

int main() {
    func(1024 * 1024 * 1024 * 1024 * 1024ull); // warning, ok
    A a(1024 * 1024 * 1024 * 1024 * 1024ull); // no warning in Clang!
}

The one in calling func is detected by Clang.
But the other one in calling A::A does not, even with -Wall -Wextra flags. At the same time both GCC and MSVC reports the warning here as well. Online demo: https://gcc.godbolt.org/z/6vGT33q1W

Related discussion: https://stackoverflow.com/q/73962573/7325599

[shafik]

So we are hitting CheckedIntArithmetic(...) in ExprConstant.cpp in both cases but for the second case it looks like CheckingForUndefinedBehavior is false and therefore no diagnostic.

[shafik]

In the first case we end up going through Expr::EvaluateForOverflow(const ASTContext &Ctx) which explicitly set it:

Info.CheckingForUndefinedBehavior = true;

So it looks like Sema::CheckForIntOverflow (Expr *E) is catching the CallExpr case which covers func(1024 * 1024 * 1024 * 1024 * 1024ull) but does not handle the CXXConstructExpr case which would handle the other case.

I did a quick fix and added:

else if (auto Construct = dyn_cast<CXXConstructExpr>(E))
      Exprs.append(Construct->arg_begin(), Construct->arg_end());

and that seems to fix the problem. If this passes a check-clang I will try and post a patch.

[shafik]

PR: https://reviews.llvm.org/D137897