sammccall added a comment.
In D107275#3214272 <https://reviews.llvm.org/D107275#3214272>, @sammccall wrote:
> In the motivating case, the subscript is a known integer type and the LHS is
> an array or pointer. In this case we don't have the above concern, and we
> also don't have my #1 above. So I'll restrict the code to cover that case.
Actually I like the restriction a lot, but this *doesn't* take care of #1.
Even with the restriction, we can still end up with a non-dependent type for
our type-dependent ArraySubscriptExpr:
Case 1: base and index do not have dependent types. One example of this is that
base can be a reference to a static member of the current instantiation that is
an array of unknown bound.
template <int>
struct foo {
static int arr[];
static constexpr int first = arr[0]; // arr is type-dependent but has
non-dependent type int[].
};
Case 2: base is an array with dependent size.
template <int N>
struct foo {
static int arr[N];
static constexpr int first = arr[0];
};
Case 3: index is a dependent type that is nevertheless known to be a good index.
static int arr[];
template <int>
struct foo {
enum E { Zero = 0; }
static constexpr int first = arr[Zero];
};
So I see two options:
- arbitrarily force the type to be dependent - if we end up with a
non-dependent type, use DependentTy instead. This "forgetting" the type is
consistent with other situations, like `this->member` inside a template, which
the standard says is type-dependent and clang assigns DependentTy.
- accept that we have type-dependent expressions of non-dependent types in some
cases. This is consistent with the idea that such exceptions exist today (the
DeclRefExpr to unknown-bound-array static members mentioned above).
I feel a little out of my depth, so I'm going to go with the "safe option" of
bailing out to DependentTy.
@rsmith or other experts, It would be great to get guidance on whether it's
safe to create type-dependent expressions without dependent types.
Repository:
rG LLVM Github Monorepo
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