clang/test/AST/ByteCode/dynalloc-limits.cpp

// RUN: %clang_cc1 -std=c++20 -verify=ref,both      -fconstexpr-steps=1024 -Wvla %s
// RUN: %clang_cc1 -std=c++20 -verify=both,both -fconstexpr-steps=1024 -Wvla %s -fexperimental-new-constant-interpreter




namespace std {
  using size_t = decltype(sizeof(0));
}

void *operator new(std::size_t, void *p) { return p; }

namespace std {
  template<typename T> struct allocator {
    constexpr T *allocate(size_t N) {
      return (T*)operator new(sizeof(T) * N); // #alloc
    }
    constexpr void deallocate(void *p) {
      operator delete(p);
    }
  };
  template<typename T, typename ...Args>
  constexpr void construct_at(void *p, Args &&...args) { // #construct
    new (p) T((Args&&)args...);
  }
}

template <typename T>
struct S {
    constexpr S(unsigned long long N)
    : data(nullptr){
        data = alloc.allocate(N);  // #call
        for(std::size_t i = 0; i < N; i ++)
            std::construct_at<T>(data + i, i); // #construct_call
    }
    constexpr T operator[](std::size_t i) const {
      return data[i];
    }

    constexpr ~S() {
        alloc.deallocate(data);
    }
    std::allocator<T> alloc;
    T* data;
};

#if __LP64__
constexpr std::size_t s = S<std::size_t>(~0UL)[42]; // both-error {{constexpr variable 's' must be initialized by a constant expression}} \
                                           // both-note-re@#call {{in call to 'this->alloc.allocate({{.*}})'}} \
                                           // both-note-re@#alloc {{cannot allocate array; evaluated array bound {{.*}} is too large}} \
                                           // both-note-re {{in call to 'S({{.*}})'}}
#endif

constexpr std::size_t ssmall = S<std::size_t>(100)[42];

constexpr std::size_t s5 = S<std::size_t>(1025)[42]; // both-error {{constexpr variable 's5' must be initialized by a constant expression}} \
                                   // both-note@#alloc {{cannot allocate array; evaluated array bound 1025 exceeds the limit (1024); use '-fconstexpr-steps' to increase this limit}} \
                                   // both-note@#call {{in call to 'this->alloc.allocate(1025)'}} \
                                   // both-note {{in call}}



template <auto N>
constexpr int stack_array() {
    [[maybe_unused]] char BIG[N] = {1};  // both-note {{cannot allocate array; evaluated array bound 1025 exceeds the limit (1024)}}
    return BIG[N-1];
}

int c = stack_array<1024>();
int d = stack_array<1025>();
constexpr int e = stack_array<1024>();
constexpr int f = stack_array<1025>(); // both-error {{constexpr variable 'f' must be initialized by a constant expression}} \
                                       // both-note {{in call}}