[Clang] Matrix types are currently not supported in constant evaluation

[Sirraide]

We support vector types, so supporting matrices as well would make sense, even though it sounds like it’d be quite a bit of work as it would probably involve adding a new APValue kind.

As an example, this (https://godbolt.org/z/WE84hhYvP):

template <typename T>
constexpr bool f() {
    T t = T();
    return true;
}

using M = int [[clang::matrix_type(4, 4)]];

static_assert(f<M>());

doesn’t work currently:

<source>:9:15: error: static assertion expression is not an integral constant expression
    9 | static_assert(f<M>());
      |               ^~~~~~
<source>:3:11: note: non-literal type 'int __attribute__((matrix_type(4, 4)))' cannot be used in a constant expression
    3 |     T t = T();
      |           ^
<source>:9:15: note: in call to 'f<int __attribute__((matrix_type(4, 4)))>()'
    9 | static_assert(f<M>());
      |               ^~~~~~

[llvmbot]

@llvm/issue-subscribers-clang-frontend

Author: None (Sirraide)

We support vector types, so supporting matrices as well would make sense, even though it sounds like it’d be quite a bit of work as it would probably involve adding a new `APValue` kind.

As an example, this (https://godbolt.org/z/WE84hhYvP):

template <typename T>
constexpr bool f() {
    T t = T();
    return true;
}

using M = int [[clang::matrix_type(4, 4)]];

static_assert(f<M>());

doesn’t work currently:

<source>:9:15: error: static assertion expression is not an integral constant expression
    9 | static_assert(f<M>());
      |               ^~~~~~
<source>:3:11: note: non-literal type 'int __attribute__((matrix_type(4, 4)))' cannot be used in a constant expression
    3 |     T t = T();
      |           ^
<source>:9:15: note: in call to 'f<int __attribute__((matrix_type(4, 4)))>()'
    9 | static_assert(f<M>());
      |               ^~~~~~