Don't infer attributes of virtual calls based on the function body

tests/codegen/virtual-call-attrs-issue-137646.rs

@@ -0,0 +1,18 @@
+//! Regression test for https://github.com/rust-lang/rust/issues/137646.
+//! Since we don't know the exact implementation of the virtual call,
+//! it might write to parameters, we can't infer the readonly attribute.
+//@ compile-flags: -C opt-level=3 -C no-prepopulate-passes
+
+#![crate_type = "lib"]
+
+pub trait Trait {
+    fn m(&self, _: (i32, i32, i32)) {}
+}
+
+#[no_mangle]
+pub fn foo(trait_: &dyn Trait) {
+    // CHECK-LABEL: @foo(
+    // CHECK: call void
+    // CHECK-NOT: readonly
+    trait_.m((1, 1, 1));
+}