fix(nvvm): use PassMode::Cast for align(16) ADTs

Author: Snehal-Reddy

crates/rustc_codegen_nvvm/src/abi.rs

@@ -59,8 +59,32 @@ pub(crate) fn readjust_fn_abi<'tcx>(
 
         // pass all adts directly as values, ptx wants them to be passed all by value, but rustc's
         // ptx-kernel abi seems to be wrong, and it's unstable.
-        if arg.layout.ty.is_adt() && !matches!(arg.mode, PassMode::Direct { .. }) {
-            arg.mode = PassMode::Direct(ArgAttributes::new());
+        if arg.layout.ty.is_adt() {
+            let align = arg.layout.align.abi.bytes();
+            if align >= 16 && align.is_power_of_two() {
+                let unit = Reg {
+                    kind: RegKind::Integer,
+                    size: Size::from_bytes(16),
+                };
+                let cast = CastTarget {
+                    prefix: Default::default(),
+                    rest: rustc_target::callconv::Uniform {
+                        unit,
+                        total: arg.layout.size,
+                        is_consecutive: false,
+                    },
+                    rest_offset: Some(Size::ZERO),
+                    attrs: ArgAttributes::new(),
+                };
+                arg.mode = PassMode::Cast {
+                    cast: Box::new(cast),
+                    pad_i32: false,
+                };
+            } else if !matches!(arg.mode, PassMode::Direct { .. }) {
+                let mut attrs = ArgAttributes::new();
+                attrs.pointee_align = Some(arg.layout.align.abi);
+                arg.mode = PassMode::Direct(attrs);
+            }
         }
         arg
     };