Introduce ConstAllocation.

Currently some `Allocation`s are interned, some are not, and it's very
hard to tell at a use point which is which.

This commit introduces `ConstAllocation` for the known-interned ones,
which makes the division much clearer. `ConstAllocation::inner()` is
used to get the underlying `Allocation`.

In some places it's natural to use an `Allocation`, in some it's natural
to use a `ConstAllocation`, and in some places there's no clear choice.
I've tried to make things look as nice as possible, while generally
favouring `ConstAllocation`, which is the type that embodies more
information. This does require quite a few calls to `inner()`.

The commit also tweaks how `PartialOrd` works for `Interned`. The
previous code was too clever by half, building on `T: Ord` to make the
code shorter. That caused problems with deriving `PartialOrd` and `Ord`
for `ConstAllocation`, so I changed it to build on `T: PartialOrd`,
which is slightly more verbose but much more standard and avoided the
problems.

src/common.rs

@@ -13,7 +13,7 @@ use rustc_codegen_ssa::traits::{
 use rustc_middle::mir::Mutability;
 use rustc_middle::ty::ScalarInt;
 use rustc_middle::ty::layout::{TyAndLayout, LayoutOf};
-use rustc_middle::mir::interpret::{Allocation, GlobalAlloc, Scalar};
+use rustc_middle::mir::interpret::{ConstAllocation, GlobalAlloc, Scalar};
 use rustc_span::Symbol;
 use rustc_target::abi::{self, HasDataLayout, Pointer, Size};
 
@@ -230,6 +230,7 @@ impl<'gcc, 'tcx> ConstMethods<'tcx> for CodegenCx<'gcc, 'tcx> {
                     match self.tcx.global_alloc(alloc_id) {
                         GlobalAlloc::Memory(alloc) => {
                             let init = const_alloc_to_gcc(self, alloc);
+                            let alloc = alloc.inner();
                             let value =
                                 match alloc.mutability {
                                     Mutability::Mut => self.static_addr_of_mut(init, alloc.align, None),
@@ -262,21 +263,21 @@ impl<'gcc, 'tcx> ConstMethods<'tcx> for CodegenCx<'gcc, 'tcx> {
         }
     }
 
-    fn const_data_from_alloc(&self, alloc: &Allocation) -> Self::Value {
+    fn const_data_from_alloc(&self, alloc: ConstAllocation<'tcx>) -> Self::Value {
         const_alloc_to_gcc(self, alloc)
     }
 
-    fn from_const_alloc(&self, layout: TyAndLayout<'tcx>, alloc: &Allocation, offset: Size) -> PlaceRef<'tcx, RValue<'gcc>> {
-        assert_eq!(alloc.align, layout.align.abi);
+    fn from_const_alloc(&self, layout: TyAndLayout<'tcx>, alloc: ConstAllocation<'tcx>, offset: Size) -> PlaceRef<'tcx, RValue<'gcc>> {
+        assert_eq!(alloc.inner().align, layout.align.abi);
         let ty = self.type_ptr_to(layout.gcc_type(self, true));
         let value =
             if layout.size == Size::ZERO {
-                let value = self.const_usize(alloc.align.bytes());
+                let value = self.const_usize(alloc.inner().align.bytes());
                 self.context.new_cast(None, value, ty)
             }
             else {
                 let init = const_alloc_to_gcc(self, alloc);
-                let base_addr = self.static_addr_of(init, alloc.align, None);
+                let base_addr = self.static_addr_of(init, alloc.inner().align, None);
 
                 let array = self.const_bitcast(base_addr, self.type_i8p());
                 let value = self.context.new_array_access(None, array, self.const_usize(offset.bytes())).get_address(None);

src/consts.rs

@@ -7,7 +7,7 @@ use rustc_middle::middle::codegen_fn_attrs::{CodegenFnAttrFlags, CodegenFnAttrs}
 use rustc_middle::mir::mono::MonoItem;
 use rustc_middle::ty::{self, Instance, Ty};
 use rustc_middle::ty::layout::LayoutOf;
-use rustc_middle::mir::interpret::{self, Allocation, ErrorHandled, Scalar as InterpScalar, read_target_uint};
+use rustc_middle::mir::interpret::{self, ConstAllocation, ErrorHandled, Scalar as InterpScalar, read_target_uint};
 use rustc_span::Span;
 use rustc_span::def_id::DefId;
 use rustc_target::abi::{self, Align, HasDataLayout, Primitive, Size, WrappingRange};
@@ -284,7 +284,8 @@ impl<'gcc, 'tcx> CodegenCx<'gcc, 'tcx> {
     }
 }
 
-pub fn const_alloc_to_gcc<'gcc, 'tcx>(cx: &CodegenCx<'gcc, 'tcx>, alloc: &Allocation) -> RValue<'gcc> {
+pub fn const_alloc_to_gcc<'gcc, 'tcx>(cx: &CodegenCx<'gcc, 'tcx>, alloc: ConstAllocation<'tcx>) -> RValue<'gcc> {
+    let alloc = alloc.inner();
     let mut llvals = Vec::with_capacity(alloc.relocations().len() + 1);
     let dl = cx.data_layout();
     let pointer_size = dl.pointer_size.bytes() as usize;
@@ -338,7 +339,7 @@ pub fn const_alloc_to_gcc<'gcc, 'tcx>(cx: &CodegenCx<'gcc, 'tcx>, alloc: &Alloca
     cx.const_struct(&llvals, true)
 }
 
-pub fn codegen_static_initializer<'gcc, 'tcx>(cx: &CodegenCx<'gcc, 'tcx>, def_id: DefId) -> Result<(RValue<'gcc>, &'tcx Allocation), ErrorHandled> {
+pub fn codegen_static_initializer<'gcc, 'tcx>(cx: &CodegenCx<'gcc, 'tcx>, def_id: DefId) -> Result<(RValue<'gcc>, ConstAllocation<'tcx>), ErrorHandled> {
     let alloc = cx.tcx.eval_static_initializer(def_id)?;
     Ok((const_alloc_to_gcc(cx, alloc), alloc))
 }