respect repr(align(N)) on functions in miri

Author: folkertdev

tests/pass/fn_align.rs

@@ -0,0 +1,21 @@
+//@compile-flags: -Zmin-function-alignment=8
+#![feature(fn_align)]
+
+// When a function uses `repr(align(N))`, the function address should be a multiple of `N`.
+
+#[repr(align(256))]
+fn foo() {}
+
+#[repr(align(16))]
+fn bar() {}
+
+#[repr(align(4))]
+fn baz() {}
+
+fn main() {
+    assert!((foo as usize).is_multiple_of(256));
+    assert!((bar as usize).is_multiple_of(16));
+
+    // The maximum of `repr(align(N))` and `-Zmin-function-alignment=N` is used.
+    assert!((baz as usize).is_multiple_of(8));
+}