compiler: Add lit test for call site attributes [nfc]

artiq/test/lit/embedding/syscall_arg_attrs.py

@@ -0,0 +1,30 @@
+# RUN: env ARTIQ_DUMP_LLVM=%t %python -m artiq.compiler.testbench.embedding +compile %s
+# RUN: OutputCheck %s --file-to-check=%t.ll
+
+from artiq.language.core import *
+from artiq.language.types import *
+
+# Make sure `byval` and `sret` are specified both at the call site and the
+# declaration. This isn't caught by the LLVM IR validator, but mismatches
+# lead to miscompilations (at least in LLVM 11).
+
+
+@kernel
+def entrypoint():
+    # CHECK: call void @accept_str\({ i8\*, i32 }\* nonnull byval
+    accept_str("foo")
+
+    # CHECK: call void @return_str\({ i8\*, i32 }\* nonnull sret
+    return_str()
+
+
+# CHECK: declare void @accept_str\({ i8\*, i32 }\* byval\)
+@syscall
+def accept_str(name: TStr) -> TNone:
+    pass
+
+
+# CHECK: declare void @return_str\({ i8\*, i32 }\* sret\)
+@syscall
+def return_str() -> TStr:
+    pass