Add a test case for rust-lang#137646

Author: dianqk

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

@@ -0,0 +1,47 @@
+//! Regression test for https://github.com/rust-lang/rust/issues/137646.
+//! FIXME: The parameter value at all calls to `check` should be `(1, 1, 1)`.
+
+//@ run-pass
+//@ check-run-results
+
+use std::hint::black_box;
+
+type T = (i32, i32, i32);
+
+pub trait Trait {
+    fn m(&self, _: T, _: T) {}
+}
+
+impl Trait for () {
+    fn m(&self, mut _v1: T, v2: T) {
+        _v1 = (0, 0, 0);
+        check(v2);
+    }
+}
+
+pub fn run_1(trait_: &dyn Trait) {
+    let v1 = (1, 1, 1);
+    let v2 = (1, 1, 1);
+    trait_.m(v1, v2);
+}
+
+pub fn run_2(trait_: &dyn Trait) {
+    let v1 = (1, 1, 1);
+    let v2 = (1, 1, 1);
+    trait_.m(v1, v2);
+    check(v1);
+    check(v2);
+}
+
+#[inline(never)]
+fn check(v: T) {
+    dbg!(v);
+    // assert_eq!(v, (1, 1, 1));
+}
+
+fn main() {
+    black_box(run_1 as fn(&dyn Trait));
+    black_box(run_2 as fn(&dyn Trait));
+    run_1(&());
+    run_2(&());
+}

tests/ui/virtual-call-attrs-issue-137646.run.stderr

@@ -0,0 +1,20 @@
+[$DIR/virtual-call-attrs-issue-137646.rs:38:5] v = (
+    498486832,
+    22093,
+    498491440,
+)
+[$DIR/virtual-call-attrs-issue-137646.rs:38:5] v = (
+    0,
+    0,
+    0,
+)
+[$DIR/virtual-call-attrs-issue-137646.rs:38:5] v = (
+    0,
+    0,
+    0,
+)
+[$DIR/virtual-call-attrs-issue-137646.rs:38:5] v = (
+    0,
+    0,
+    0,
+)