This is step 1 of exposing WASM `ref.func` to LLVM.

This PR only handles creating the instruction and a test for assembling
it.

Tests if the runtime type of the function pointer matches the static
type. If this returns false, calling the function pointer will trap.
Uses `@llvm.wasm.ref.test.func` added in #147486.

Also adds a "gc" wasm feature to gate the use of the ref.test
instruction.

This will allow us to eliminate the hand-coded webassembly here:

https://github.com/python/cpython/blob/main/Python/emscripten_trampoline.c#L138

This adds (back) the exnref type restored in the new EH proposal adopted
in Oct 2023 CG meeting:

https://github.com/WebAssembly/exception-handling/blob/main/proposals/exception-handling/Exceptions.md:x

Custom type-checking (in WebAssemblyAsmTypeCheck.cpp) is used to
workaround the fact that separate variants of the instruction are
defined for externref and funcref.

Based on an initial patch by Paulo Matos <pmatos@igalia.com>.

Differential Revision: https://reviews.llvm.org/D123484

This patch implements the intrinsic for ref.null.
In the process of implementing int_wasm_ref_null_func() and
int_wasm_ref_null_extern() intrinsics, it removes the redundant
HeapType.

This also causes the textual assembler syntax for ref.null to
change. Instead of receiving an argument: `func` or `extern`, the
instruction mnemonic is either ref.null_func or ref.null_extern,
without the need for a further operand.

Reviewed By: tlively

Differential Revision: https://reviews.llvm.org/D114979

This patch adds support for WebAssembly globals in LLVM IR, representing
them as pointers to global values, in a non-default, non-integral
address space.  Instruction selection legalizes loads and stores to
these pointers to new WebAssemblyISD nodes GLOBAL_GET and GLOBAL_SET.
Once the lowering creates the new nodes, tablegen pattern matches those
and converts them to Wasm global.get/set of the appropriate type.

Based on work by Paulo Matos in https://reviews.llvm.org/D95425.

Reviewed By: pmatos

Differential Revision: https://reviews.llvm.org/D101608

This removes `exnref` type and `br_on_exn` instruction. This is
effectively NFC because most uses of these were already removed in the
previous CLs.

Reviewed By: dschuff, tlively

Differential Revision: https://reviews.llvm.org/D94041

This adds missing `select` instruction support and block return type
support for reference types. Also refactors WebAssemblyInstrRef.td and
rearranges tests in reference-types.s. Tests don't include `exnref`
types, because we currently don't support `exnref` for `ref.null` and
the type will be removed soon anyway.

Reviewed By: tlively, sbc100, wingo

Differential Revision: https://reviews.llvm.org/D92359

This patch adds a new "heap type" operand kind to the WebAssembly MC
layer, used by ref.null. Currently the possible values are "extern" and
"func"; when typed function references come, though, this operand may be
a type index.

Note that the "heap type" production is still known as "refedtype" in
the draft proposal; changing its name in the spec is
ongoing (https://github.com/WebAssembly/reference-types/issues/123).

The register form of ref.null is still untested.

Differential Revision: https://reviews.llvm.org/D90608