ctfe interpreter: extend provenance so that it can track whether a pointer is immutable

Author: RalfJung

src/common.rs

@@ -199,7 +199,8 @@ impl<'gcc, 'tcx> ConstMethods<'tcx> for CodegenCx<'gcc, 'tcx> {
                 }
             }
             Scalar::Ptr(ptr, _size) => {
-                let (alloc_id, offset) = ptr.into_parts();
+                let (prov, offset) = ptr.into_parts(); // we know the `offset` is relative
+                let alloc_id = prov.alloc_id();
                 let base_addr =
                     match self.tcx.global_alloc(alloc_id) {
                         GlobalAlloc::Memory(alloc) => {

src/consts.rs

@@ -285,7 +285,8 @@ pub fn const_alloc_to_gcc<'gcc, 'tcx>(cx: &CodegenCx<'gcc, 'tcx>, alloc: ConstAl
     let pointer_size = dl.pointer_size.bytes() as usize;
 
     let mut next_offset = 0;
-    for &(offset, alloc_id) in alloc.provenance().ptrs().iter() {
+    for &(offset, prov) in alloc.provenance().ptrs().iter() {
+        let alloc_id = prov.alloc_id();
         let offset = offset.bytes();
         assert_eq!(offset as usize as u64, offset);
         let offset = offset as usize;
@@ -313,7 +314,7 @@ pub fn const_alloc_to_gcc<'gcc, 'tcx>(cx: &CodegenCx<'gcc, 'tcx>, alloc: ConstAl
 
         llvals.push(cx.scalar_to_backend(
             InterpScalar::from_pointer(
-                interpret::Pointer::new(alloc_id, Size::from_bytes(ptr_offset)),
+                interpret::Pointer::new(prov, Size::from_bytes(ptr_offset)),
                 &cx.tcx,
             ),
             abi::Scalar::Initialized { value: Primitive::Pointer(address_space), valid_range: WrappingRange::full(dl.pointer_size) },