[PATCH] D139010: [clang][WebAssembly] Implement support for table types and builtins

[Aaron Ballman via Phabricator via cfe-commits]

aaron.ballman added inline comments.


================
Comment at: clang/docs/LanguageExtensions.rst:2288
+argument is the index to which to store the value into, and the
+third argument is a value of reference type to store in the table.
+It returns nothing.
----------------
pmatos wrote:
> aaron.ballman wrote:
> > This sounds like any reference type will work, e.g.,
> > ```
> > static __externref_t table[0];
> > void func(int i) {
> >   int &ref = i;
> >   __builtin_wasm_table_set(table, i, ref);
> > }
> > ```
> > so might want to say "value of ``_externref_t`` type" instead?
> Any reference type will work, i.e. externref or funcref. You can also store funcrefs in a wasm table. But of course, it needs to be well-typed. You cannot store a funcref value in an externref table and vice-versa.
My point is more that "any reference type" suggests you can use an arbitrary C++ reference type like `int &` and I think we mean something more specific than that, right?


================
Comment at: clang/docs/LanguageExtensions.rst:2364-2365
+range, the third argument is the value to set in the new entries, and 
+the fourth and the last argument is the size of the range. It returns 
+nothing.
+
----------------
pmatos wrote:
> aaron.ballman wrote:
> > What happens if the range is invalid for the table size? e.g., the user never called `__builtin_wasm_table_grow` before calling `__builtin_wasm_table_fill`?
> The host executing the WebAssembly instance will trap. This is part of the WebAssembly spec.
Hmmm, do you think we should mention that here? Alternatively, should we have a link to other WebAssembly documentation so we can say "see <blah> for more details?" to avoid replicating docs too much?


================
Comment at: clang/test/SemaCXX/wasm-refs-and-tables.cpp:35
+task<__externref_t[]> g() {
+  co_return table;
+}
----------------
pmatos wrote:
> aaron.ballman wrote:
> > pmatos wrote:
> > > @aaron.ballman I tried and failed to create a good testcase for co_return. However creating coroutines seems to be an stdlib thing which I am not sure how to test here. Do you have any suggestions here?
> > ```
> > #include "Inputs/std-coroutine.h"
> > 
> > using std::suspend_always;
> > 
> > struct promise_table {
> >   __externref_t[] get_return_object();
> >   suspend_always initial_suspend();
> >   suspend_always final_suspend() noexcept;
> >   void return_value(__externref_t[]);
> >   void unhandled_exception();
> > };
> > 
> > template <typename... T>
> > struct std::coroutine_traits<__externref_t[], T...> { using promise_type = promise_table; };
> > 
> > static __externref_t table[0];
> > __externref_t[] func() {
> >   co_return table; // Cannot return a WebAssembly table?
> > }
> > ```
> > Perhaps something along these lines?
> But you cannot write promise_table because a table cannot be an argument in return_value. Also, you cannot return a table in get_return_object. Doesn't this invalidate straight away the use of a table with co-routines?
Ah! Yeah, I think that does. Okay, let's punt on coroutines, that's turning out to be a slog.


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https://reviews.llvm.org/D139010