Fix transmutes between vectors and integers

Fixes #1102

src/value_and_place.rs

@@ -332,7 +332,7 @@ impl<'tcx> CPlace<'tcx> {
 
         let stack_slot = fx.bcx.create_stack_slot(StackSlotData {
             kind: StackSlotKind::ExplicitSlot,
-            size: layout.size.bytes() as u32,
+            size: u32::try_from(layout.size.bytes()).unwrap(),
             offset: None,
         });
         CPlace {
@@ -530,6 +530,13 @@ impl<'tcx> CPlace<'tcx> {
             dst_ty: Type,
         ) {
             let src_ty = fx.bcx.func.dfg.value_type(data);
+            assert_eq!(
+                src_ty.bytes(),
+                dst_ty.bytes(),
+                "write_cvalue_transmute: {:?} -> {:?}",
+                src_ty,
+                dst_ty,
+            );
             let data = match (src_ty, dst_ty) {
                 (_, _) if src_ty == dst_ty => data,
 
@@ -541,6 +548,17 @@ impl<'tcx> CPlace<'tcx> {
                 _ if src_ty.is_vector() && dst_ty.is_vector() => {
                     fx.bcx.ins().raw_bitcast(dst_ty, data)
                 }
+                _ if src_ty.is_vector() || dst_ty.is_vector() => {
+                    // FIXME do something more efficient for transmutes between vectors and integers.
+                    let stack_slot = fx.bcx.create_stack_slot(StackSlotData {
+                        kind: StackSlotKind::ExplicitSlot,
+                        size: src_ty.bytes(),
+                        offset: None,
+                    });
+                    let ptr = Pointer::stack_slot(stack_slot);
+                    ptr.store(fx, data, MemFlags::trusted());
+                    ptr.load(fx, dst_ty, MemFlags::trusted())
+                }
                 _ => unreachable!("write_cvalue_transmute: {:?} -> {:?}", src_ty, dst_ty),
             };
             fx.bcx