mv compiler to compiler/

compiler/rustc_mir/src/util/alignment.rs

@@ -0,0 +1,60 @@
+use rustc_middle::mir::*;
+use rustc_middle::ty::{self, TyCtxt};
+
+/// Returns `true` if this place is allowed to be less aligned
+/// than its containing struct (because it is within a packed
+/// struct).
+pub fn is_disaligned<'tcx, L>(
+    tcx: TyCtxt<'tcx>,
+    local_decls: &L,
+    param_env: ty::ParamEnv<'tcx>,
+    place: Place<'tcx>,
+) -> bool
+where
+    L: HasLocalDecls<'tcx>,
+{
+    debug!("is_disaligned({:?})", place);
+    if !is_within_packed(tcx, local_decls, place) {
+        debug!("is_disaligned({:?}) - not within packed", place);
+        return false;
+    }
+
+    let ty = place.ty(local_decls, tcx).ty;
+    match tcx.layout_raw(param_env.and(ty)) {
+        Ok(layout) if layout.align.abi.bytes() == 1 => {
+            // if the alignment is 1, the type can't be further
+            // disaligned.
+            debug!("is_disaligned({:?}) - align = 1", place);
+            false
+        }
+        _ => {
+            debug!("is_disaligned({:?}) - true", place);
+            true
+        }
+    }
+}
+
+fn is_within_packed<'tcx, L>(tcx: TyCtxt<'tcx>, local_decls: &L, place: Place<'tcx>) -> bool
+where
+    L: HasLocalDecls<'tcx>,
+{
+    let mut cursor = place.projection.as_ref();
+    while let &[ref proj_base @ .., elem] = cursor {
+        cursor = proj_base;
+
+        match elem {
+            // encountered a Deref, which is ABI-aligned
+            ProjectionElem::Deref => break,
+            ProjectionElem::Field(..) => {
+                let ty = Place::ty_from(place.local, proj_base, local_decls, tcx).ty;
+                match ty.kind {
+                    ty::Adt(def, _) if def.repr.packed() => return true,
+                    _ => {}
+                }
+            }
+            _ => {}
+        }
+    }
+
+    false
+}