https://bugs.llvm.org/show_bug.cgi?id=50962
Bug ID: 50962
Summary: Clang 11.0 and 12.0 errorneous codegen on Windows x64
when using Visual Studio 2019 STL.
Product: clang
Version: 12.0
Hardware: PC
OS: Windows NT
Status: NEW
Severity: release blocker
Priority: P
Component: C++17
Assignee: [email protected]
Reporter: [email protected]
CC: [email protected], [email protected],
[email protected], [email protected]
Rephrased title to better match the problem, originally from [Structured
Bindings Miscompilation(?) on Windows
x64](https://bugs.llvm.org/show_bug.cgi?id=50731). As the problem is not
limited to structured bindings but operator[] and std::get.
Microsoft also doesn't seem to find anything wrong with their STL, for more
info, see [Clang 11.0 and 12.0 generates erroneous code when using
STL](https://developercommunity.visualstudio.com/t/Clang-110-and-120-generates-erroneous/1464106).
The code in question,
```
#include <immintrin.h>
#include <array>
namespace my {
template <class T, size_t N>
struct array {
T data_[N];
};
template <size_t I, class T, size_t N>
constexpr typename std::enable_if<(I < N), T&>::type get(
my::array<T, N>& a) noexcept {
return a.data_[I];
}
template <size_t I, class T, size_t N>
constexpr typename std::enable_if<(I < N), T const&>::type get(
my::array<T, N> const& a) noexcept {
return a.data_[I];
}
template <size_t I, class T, size_t N>
constexpr typename std::enable_if<(I < N), T&&>::type get(
my::array<T, N>&& a) noexcept {
return std::move(a.data_[I]);
}
} // namespace my
namespace std {
template <class T, size_t N>
struct tuple_size<my::array<T, N>> {
static constexpr auto value = N;
};
template <size_t I, class T, size_t N>
struct tuple_element<I, my::array<T, N>> {
static_assert(I < N);
using type = T;
};
} // namespace std
#if 0
using std::array; // Results in memory violation in x64 Debug.
#else
using my::array; // Fine.
#endif
int main() {
auto lambda = [](std::array<__m256i, 2> in) noexcept {
auto [in0, in1] = in;
return _mm256_add_epi8(in0, in1);
};
const __m256i a = _mm256_set1_epi8(1);
const __m256i b = _mm256_set1_epi8(2);
(void)lambda({a, b});
}
```
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