r290577 - Add a test for `const` folding introduced by r290297. NFC.

[Richard Smith via cfe-commits]

On 26 December 2016 at 20:01, George Burgess IV via cfe-commits <
cfe-commits at lists.llvm.org> wrote:

> Author: gbiv
> Date: Mon Dec 26 22:01:22 2016
> New Revision: 290577
>
> URL: http://llvm.org/viewvc/llvm-project?rev=290577&view=rev
> Log:
> Add a test for `const` folding introduced by r290297. NFC.
>
> AFAICT, we didn't add a test targeted at the new "const can sometimes
> act as constexpr" behavior introduced by r290297.
>
> Modified:
>     cfe/trunk/test/SemaCXX/constant-expression-cxx1y.cpp
>
> Modified: cfe/trunk/test/SemaCXX/constant-expression-cxx1y.cpp
> URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/test/
> SemaCXX/constant-expression-cxx1y.cpp?rev=290577&r1=
> 290576&r2=290577&view=diff
> ============================================================
> ==================
> --- cfe/trunk/test/SemaCXX/constant-expression-cxx1y.cpp (original)
> +++ cfe/trunk/test/SemaCXX/constant-expression-cxx1y.cpp Mon Dec 26
> 22:01:22 2016
> @@ -957,3 +957,20 @@ namespace PR27989 {
>    }
>    static_assert(f(0) == 1, "");
>  }
> +
> +namespace const_char {
> +template <int M, int N>
> +constexpr int sum(const char (&Arr)[N]) {
> +  static_assert(N >= M, "");
> +  int S = 0;
> +  for (unsigned I = 0; I != M; ++I)
> +    S += Arr[I];
> +  return S;
> +}
> +
> +// As an extension, we support evaluating some things that are `const` as
> though
> +// they were `constexpr`.
> +const char Cs[] = {'a', 'b', 'c'};
> +const int N = 2;
> +static_assert(sum<N>(Cs) == 'a' + 'b', "");
> +}


Hold on, this test should fail. It's OK to extend the set of things we can
constant-fold, but formal constant expression checking still needs to be
strict. (You should produce a CCEDiag from within the constant expression
evaluator to mark things that are not core constant expressions but are
permitted as an extension.)
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