support creating mutable allocations from byte slices

Author: RalfJung

compiler/rustc_middle/src/mir/interpret/allocation.rs

@@ -100,21 +100,25 @@ impl AllocRange {
 // The constructors are all without extra; the extra gets added by a machine hook later.
 impl<Tag> Allocation<Tag> {
     /// Creates a read-only allocation initialized by the given bytes
-    pub fn from_bytes<'a>(slice: impl Into<Cow<'a, [u8]>>, align: Align) -> Self {
+    pub fn from_bytes<'a>(
+        slice: impl Into<Cow<'a, [u8]>>,
+        align: Align,
+        mutability: Mutability,
+    ) -> Self {
         let bytes = slice.into().into_owned();
         let size = Size::from_bytes(bytes.len());
         Self {
             bytes,
             relocations: Relocations::new(),
             init_mask: InitMask::new(size, true),
             align,
-            mutability: Mutability::Not,
+            mutability,
             extra: (),
         }
     }
 
-    pub fn from_byte_aligned_bytes<'a>(slice: impl Into<Cow<'a, [u8]>>) -> Self {
-        Allocation::from_bytes(slice, Align::ONE)
+    pub fn from_bytes_byte_aligned_immutable<'a>(slice: impl Into<Cow<'a, [u8]>>) -> Self {
+        Allocation::from_bytes(slice, Align::ONE, Mutability::Not)
     }
 
     pub fn uninit(size: Size, align: Align) -> Self {

compiler/rustc_middle/src/ty/context.rs

@@ -1072,7 +1072,7 @@ impl<'tcx> TyCtxt<'tcx> {
     /// Allocates a read-only byte or string literal for `mir::interpret`.
     pub fn allocate_bytes(self, bytes: &[u8]) -> interpret::AllocId {
         // Create an allocation that just contains these bytes.
-        let alloc = interpret::Allocation::from_byte_aligned_bytes(bytes);
+        let alloc = interpret::Allocation::from_bytes_byte_aligned_immutable(bytes);
         let alloc = self.intern_const_alloc(alloc);
         self.create_memory_alloc(alloc)
     }

compiler/rustc_mir/src/const_eval/eval_queries.rs

@@ -169,8 +169,9 @@ pub(super) fn op_to_const<'tcx>(
                         (ecx.tcx.global_alloc(ptr.alloc_id).unwrap_memory(), ptr.offset.bytes())
                     }
                     Scalar::Int { .. } => (
-                        ecx.tcx
-                            .intern_const_alloc(Allocation::from_byte_aligned_bytes(b"" as &[u8])),
+                        ecx.tcx.intern_const_alloc(Allocation::from_bytes_byte_aligned_immutable(
+                            b"" as &[u8],
+                        )),
                         0,
                     ),
                 };

compiler/rustc_mir/src/interpret/intrinsics/caller_location.rs

@@ -1,5 +1,6 @@
 use std::convert::TryFrom;
 
+use rustc_ast::Mutability;
 use rustc_hir::lang_items::LangItem;
 use rustc_middle::mir::TerminatorKind;
 use rustc_middle::ty::subst::Subst;
@@ -79,7 +80,8 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
         line: u32,
         col: u32,
     ) -> MPlaceTy<'tcx, M::PointerTag> {
-        let file = self.allocate_str(&filename.as_str(), MemoryKind::CallerLocation);
+        let file =
+            self.allocate_str(&filename.as_str(), MemoryKind::CallerLocation, Mutability::Not);
         let line = Scalar::from_u32(line);
         let col = Scalar::from_u32(col);
 

compiler/rustc_mir/src/interpret/intrinsics/type_name.rs

@@ -197,6 +197,6 @@ impl Write for AbsolutePathPrinter<'_> {
 /// Directly returns an `Allocation` containing an absolute path representation of the given type.
 crate fn alloc_type_name<'tcx>(tcx: TyCtxt<'tcx>, ty: Ty<'tcx>) -> &'tcx Allocation {
     let path = AbsolutePathPrinter { tcx, path: String::new() }.print_type(ty).unwrap().path;
-    let alloc = Allocation::from_byte_aligned_bytes(path.into_bytes());
+    let alloc = Allocation::from_bytes_byte_aligned_immutable(path.into_bytes());
     tcx.intern_const_alloc(alloc)
 }

compiler/rustc_mir/src/interpret/memory.rs

@@ -219,9 +219,11 @@ impl<'mir, 'tcx, M: Machine<'mir, 'tcx>> Memory<'mir, 'tcx, M> {
     pub fn allocate_bytes(
         &mut self,
         bytes: &[u8],
+        align: Align,
         kind: MemoryKind<M::MemoryKind>,
+        mutability: Mutability,
     ) -> Pointer<M::PointerTag> {
-        let alloc = Allocation::from_byte_aligned_bytes(bytes);
+        let alloc = Allocation::from_bytes(bytes, align, mutability);
         self.allocate_with(alloc, kind)
     }
 

compiler/rustc_mir/src/interpret/place.rs

@@ -6,6 +6,7 @@ use std::convert::TryFrom;
 use std::fmt::Debug;
 use std::hash::Hash;
 
+use rustc_ast::Mutability;
 use rustc_macros::HashStable;
 use rustc_middle::mir;
 use rustc_middle::ty::layout::{PrimitiveExt, TyAndLayout};
@@ -1024,18 +1025,23 @@ where
         MPlaceTy::from_aligned_ptr(ptr, layout)
     }
 
-    /// Returns a wide MPlace.
+    /// Returns a wide MPlace of type `&'static [mut] str` to a new 1-aligned allocation.
     pub fn allocate_str(
         &mut self,
         str: &str,
         kind: MemoryKind<M::MemoryKind>,
+        mutbl: Mutability,
     ) -> MPlaceTy<'tcx, M::PointerTag> {
-        let ptr = self.memory.allocate_bytes(str.as_bytes(), kind);
+        let ptr = self.memory.allocate_bytes(str.as_bytes(), Align::ONE, kind, mutbl);
         let meta = Scalar::from_machine_usize(u64::try_from(str.len()).unwrap(), self);
         let mplace =
             MemPlace { ptr: ptr.into(), align: Align::ONE, meta: MemPlaceMeta::Meta(meta) };
 
-        let layout = self.layout_of(self.tcx.mk_static_str()).unwrap();
+        let ty = self.tcx.mk_ref(
+            self.tcx.lifetimes.re_static,
+            ty::TypeAndMut { ty: self.tcx.types.str_, mutbl },
+        );
+        let layout = self.layout_of(ty).unwrap();
         MPlaceTy { mplace, layout }
     }
 

compiler/rustc_mir_build/src/thir/constant.rs

@@ -25,14 +25,14 @@ crate fn lit_to_const<'tcx>(
     let lit = match (lit, &ty.kind()) {
         (ast::LitKind::Str(s, _), ty::Ref(_, inner_ty, _)) if inner_ty.is_str() => {
             let s = s.as_str();
-            let allocation = Allocation::from_byte_aligned_bytes(s.as_bytes());
+            let allocation = Allocation::from_bytes_byte_aligned_immutable(s.as_bytes());
             let allocation = tcx.intern_const_alloc(allocation);
             ConstValue::Slice { data: allocation, start: 0, end: s.len() }
         }
         (ast::LitKind::ByteStr(data), ty::Ref(_, inner_ty, _))
             if matches!(inner_ty.kind(), ty::Slice(_)) =>
         {
-            let allocation = Allocation::from_byte_aligned_bytes(data as &[u8]);
+            let allocation = Allocation::from_bytes_byte_aligned_immutable(data as &[u8]);
             let allocation = tcx.intern_const_alloc(allocation);
             ConstValue::Slice { data: allocation, start: 0, end: data.len() }
         }