[clang] [WebAssembly,clang] Add __builtin_wasm_test_function_pointer_signature (PR #150201)

[Thomas Lively via cfe-commits]

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@@ -199,6 +199,12 @@ TARGET_BUILTIN(__builtin_wasm_ref_is_null_extern, "ii", "nct", "reference-types"
 // return type.
 TARGET_BUILTIN(__builtin_wasm_ref_null_func, "i", "nct", "reference-types")
 
+// Check if the runtime type of a function pointer matches its static type. Used
+// to avoid "function signature mismatch" traps. Takes a function pointer, uses
+// table.get to look up the pointer in __indirect_function_table and then
+// ref.test to test the type.
+TARGET_BUILTIN(__builtin_wasm_test_function_pointer_signature, "i.", "nct", "reference-types")
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tlively wrote:

`ref.test` is only added with the GC proposal, so if we emit it with only reference-types enabled, the resulting binary will not validate in wasm-opt. We need to introduce a new `gc` feature that puts `"gc"` in the target features section, then make this builtin depend on that new feature.

https://github.com/llvm/llvm-project/pull/150201