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

[Derek Schuff via llvm-commits]

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@@ -218,6 +221,64 @@ Value *CodeGenFunction::EmitWebAssemblyBuiltinExpr(unsigned BuiltinID,
     Function *Callee = CGM.getIntrinsic(Intrinsic::wasm_ref_null_func);
     return Builder.CreateCall(Callee);
   }
+  case WebAssembly::BI__builtin_wasm_test_function_pointer_signature: {
+    Value *FuncRef = EmitScalarExpr(E->getArg(0));
+
+    // Get the function type from the argument's static type
+    QualType ArgType = E->getArg(0)->getType();
+    const PointerType *PtrTy = ArgType->getAs<PointerType>();
+    assert(PtrTy && "Sema should have ensured this is a function pointer");
+
+    const FunctionType *FuncTy = PtrTy->getPointeeType()->getAs<FunctionType>();
+    assert(FuncTy && "Sema should have ensured this is a function pointer");
+
+    // In the llvm IR, we won't have access any more to the type of the function
+    // pointer so we need to insert this type information somehow. The
+    // @llvm.wasm.ref.test.func takes varargs arguments whose values are unused
+    // to indicate the type of the function to test for. See the test here:
+    // llvm/test/CodeGen/WebAssembly/ref-test-func.ll
+    //
+    // The format is: first we include the return types (since this is a C
+    // function pointer, there will be 0 or one of these) then a token type to
+    // indicate the boundary between return types and param types, then the
+    // param types.
+
+    llvm::FunctionType *LLVMFuncTy =
+        cast<llvm::FunctionType>(ConvertType(QualType(FuncTy, 0)));
+
+    uint NParams = LLVMFuncTy->getNumParams();
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dschuff wrote:

Turns out I can just directly edit. Let's see if this passes CI.

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