Make sure std::panic::Location::caller() gets optimized away.

src/test/codegen/track_caller_inlined.rs

@@ -0,0 +1,28 @@
+// This test makes sure that calls to std::panic::Location::caller()
+// don't result in an actual function call. The caller location is
+// known at compile time so the call can always be optimized away.
+
+// compile-flags: -Copt-level=2
+
+#![crate_type = "lib"]
+#![feature(bench_black_box)]
+
+// The first check makes sure that the caller location is used at all,
+// i.e. that std::hint::black_box() works.
+// CHECK: %0 = alloca %"core::panic::location::Location"*
+
+// This check makes sure that no call to `std::panic::Location::caller()`
+// is emitted. The sequence of characters is valid for both v0 and legacy
+// mangling.
+// CHECK-NOT: call {{.*}}8Location6caller
+
+// CHECK: call void asm sideeffect {{.*}}(%"core::panic::location::Location"** nonnull %0)
+
+#[track_caller]
+fn foo() {
+    std::hint::black_box(std::panic::Location::caller());
+}
+
+pub fn bar() {
+    foo();
+}