Merge #1188

1188: Support align and packed repr layout on structs r=dafaust a=dafaust

This is a start at handling the various layout options supported by Rust, beginning with `#[repr(align(N))]` and `#[repr(packed(N))]`, on structs and tuple structs.

There are several other layout options which remain to be supported such as `#[repr(C)]`, `#[repr(transparent)]`, combinations e.g. `#[repr(C, packed(2))]`, as well as layouts on union and enum types.

Fixes: #915 

Co-authored-by: David Faust <david.faust@oracle.com>

1 files changed, 20 insertions, 0 deletions

diff --git a/gcc/rust/backend/rust-compile-type.cc b/gcc/rust/backend/rust-compile-type.cc
index 07b95c7..16029ba 100644
--- a/gcc/rust/backend/rust-compile-type.cc
+++ b/gcc/rust/backend/rust-compile-type.cc
@@ -280,6 +280,26 @@ TyTyResolveCompile::visit (const TyTy::ADTType &type)
       type_record = ctx->get_backend ()->union_type (enum_fields);
     }
 
+  // Handle repr options
+  // TODO: "packed" should only narrow type alignment and "align" should only
+  // widen it. Do we need to check and enforce this here, or is it taken care of
+  // later on in the gcc middle-end?
+  TyTy::ADTType::ReprOptions repr = type.get_repr_options ();
+  if (repr.pack)
+    {
+      TYPE_PACKED (type_record);
+      if (repr.pack > 1)
+	{
+	  SET_TYPE_ALIGN (type_record, repr.pack * 8);
+	  TYPE_USER_ALIGN (type_record) = 1;
+	}
+    }
+  else if (repr.align)
+    {
+      SET_TYPE_ALIGN (type_record, repr.align * 8);
+      TYPE_USER_ALIGN (type_record) = 1;
+    }
+
   std::string named_struct_str
     = type.get_ident ().path.get () + type.subst_as_string ();
   tree named_struct