tbaeder added inline comments.
================
Comment at: clang/lib/AST/Interp/PrimType.h:108
+ switch (Expr) {
\
+ TYPE_SWITCH_CASE(PT_Sint8, B)
\
+ TYPE_SWITCH_CASE(PT_Uint8, B)
\
----------------
aaron.ballman wrote:
> tbaeder wrote:
> > tbaeder wrote:
> > > aaron.ballman wrote:
> > > > tbaeder wrote:
> > > > > aaron.ballman wrote:
> > > > > > Oh boy, this is going to be interesting, isn't it?
> > > > > > ```
> > > > > > consteval _Complex _BitInt(12) UhOh() { return (_Complex
> > > > > > _BitInt(12))1; }
> > > > > > consteval _Complex _BitInt(18) Why() { return (_Complex
> > > > > > _BitInt(18))1; }
> > > > > >
> > > > > > static_assert(UhOh() + Why() == 2);
> > > > > > ```
> > > > > >
> > > > > `_BitInt` isn't supported in the new interpreter at all right now, so
> > > > > this just gets rejected.
> > > > >
> > > > >
> > > > > Apart from that... is a complex bitint really something that should
> > > > > be supported? Not just in the new interpreter but generally?
> > > > > _BitInt isn't supported in the new interpreter at all right now, so
> > > > > this just gets rejected.
> > > >
> > > > Well, that's sort of good then! :-D We'll have to deal with `_BitInt`
> > > > at some point, so maybe we can add this as a test case with expected
> > > > failures and a fixit comment so we don't forget about it?
> > > >
> > > > > Apart from that... is a complex bitint really something that should
> > > > > be supported? Not just in the new interpreter but generally?
> > > >
> > > > I don't see why not; we support complex integer types and `_BitInt` is
> > > > an integer type. We support `_Complex` from C in C++ and we support
> > > > `_BitInt` from C in C++, so it seems reasonable to expect `_Complex
> > > > _BitInt` to work.
> > > > I don't see why not; we support complex integer types and _BitInt is an
> > > > integer type. We support _Complex from C in C++ and we support _BitInt
> > > > from C in C++, so it seems reasonable to expect _Complex _BitInt to
> > > > work.
> > >
> > > My immediate reaction to something like `_Complex` is "this is stupid,
> > > this belongs in user code". For floating-point values it at least makes
> > > sense from a mathematical POV I guess. But complex ints is already weird
> > > and complex arbitrary-width integers? What's the use case? `_Complex
> > > bool` is rejected as well after all.
> > > We'll have to deal with _BitInt at some point, so maybe we can add this
> > > as a test case with expected failures and a fixit comment so we don't
> > > forget about it?
> >
> > It's running into an assertion for the test case, so I added it
> > commented-out.
> > My immediate reaction to something like _Complex is "this is stupid, this
> > belongs in user code". For floating-point values it at least makes sense
> > from a mathematical POV I guess. But complex ints is already weird and
> > complex arbitrary-width integers? What's the use case? _Complex bool is
> > rejected as well after all.
>
> How would you explain this?
> ```
> _Complex int32_t Val; // OK
> _Complex _BitInt(32) OtherVal; // Not OK
> ```
> The use case is the same as for `_Complex int`, just with getting to pick the
> width you want to use, which users can already do for some specific widths.
> Neither is a particularly strong motivation (to me anyway!), but I can't see
> why we'd allow a 32-bit integer but not a 32-bit (et al) precise integer.
Sure, the bitint one is just a bit crazier, I was hoping we could draw the line
a little earlier and save ourselves some headaches, but this doesn't seem to be
a problem in the current interpreter.
With `constexpr` being in c++ now and c++20 having enough to implement complex
numbers in user code anyway, are there any plans to deprecate `_Complex` in
c++20 onward (not sure about C2x)? That doesn't help me of course but it would
maybe give me more hope for the future :)
Repository:
rG LLVM Github Monorepo
CHANGES SINCE LAST ACTION
https://reviews.llvm.org/D146408/new/
https://reviews.llvm.org/D146408
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