Add cache for allocate_str

Author: adwinwhite

compiler/rustc_const_eval/src/interpret/place.rs

@@ -1001,7 +1001,20 @@ where
         kind: MemoryKind<M::MemoryKind>,
         mutbl: Mutability,
     ) -> InterpResult<'tcx, MPlaceTy<'tcx, M::Provenance>> {
-        let ptr = self.allocate_bytes_ptr(str.as_bytes(), Align::ONE, kind, mutbl)?;
+        let tcx = self.tcx.tcx;
+
+        // Use cache for immutable strings.
+        let ptr = if mutbl.is_not()
+            && matches!(kind, MemoryKind::CallerLocation | MemoryKind::Machine(_))
+        {
+            // Same id for cached allocations.
+            let id = tcx.allocate_bytes(str.as_bytes());
+
+            // Turn untagged "global" pointers (obtained via `tcx`) into the machine pointer to the allocation.
+            M::adjust_alloc_root_pointer(&self, Pointer::from(id), Some(kind))?
+        } else {
+            self.allocate_bytes_ptr(str.as_bytes(), Align::ONE, kind, mutbl)?
+        };
         let meta = Scalar::from_target_usize(u64::try_from(str.len()).unwrap(), self);
         let layout = self.layout_of(self.tcx.types.str_).unwrap();
         Ok(self.ptr_with_meta_to_mplace(ptr.into(), MemPlaceMeta::Meta(meta), layout))

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

@@ -381,7 +381,6 @@ pub(crate) struct AllocMap<'tcx> {
     alloc_map: FxHashMap<AllocId, GlobalAlloc<'tcx>>,
 
     /// Used to ensure that statics and functions only get one associated `AllocId`.
-    /// Should never contain a `GlobalAlloc::Memory`!
     //
     // FIXME: Should we just have two separate dedup maps for statics and functions each?
     dedup: FxHashMap<GlobalAlloc<'tcx>, AllocId>,
@@ -421,14 +420,8 @@ impl<'tcx> TyCtxt<'tcx> {
     }
 
     /// Reserves a new ID *if* this allocation has not been dedup-reserved before.
-    /// Should only be used for "symbolic" allocations (function pointers, vtables, statics), we
-    /// don't want to dedup IDs for "real" memory!
     fn reserve_and_set_dedup(self, alloc: GlobalAlloc<'tcx>) -> AllocId {
         let mut alloc_map = self.alloc_map.lock();
-        match alloc {
-            GlobalAlloc::Function(..) | GlobalAlloc::Static(..) | GlobalAlloc::VTable(..) => {}
-            GlobalAlloc::Memory(..) => bug!("Trying to dedup-reserve memory with real data!"),
-        }
         if let Some(&alloc_id) = alloc_map.dedup.get(&alloc) {
             return alloc_id;
         }
@@ -439,6 +432,12 @@ impl<'tcx> TyCtxt<'tcx> {
         id
     }
 
+    /// Generates an `AllocId` for a memory allocation. If the exact same memory has been
+    /// allocated before, this will return the same `AllocId`.
+    pub fn reserve_and_set_memory_dedup(self, mem: ConstAllocation<'tcx>) -> AllocId {
+        self.reserve_and_set_dedup(GlobalAlloc::Memory(mem))
+    }
+
     /// Generates an `AllocId` for a static or return a cached one in case this function has been
     /// called on the same static before.
     pub fn reserve_and_set_static_alloc(self, static_id: DefId) -> AllocId {

compiler/rustc_middle/src/ty/context.rs

@@ -1394,11 +1394,12 @@ impl<'tcx> TyCtxt<'tcx> {
     }
 
     /// Allocates a read-only byte or string literal for `mir::interpret`.
+    /// Returns the same `AllocId` if called again with the same bytes.
     pub fn allocate_bytes(self, bytes: &[u8]) -> interpret::AllocId {
         // Create an allocation that just contains these bytes.
         let alloc = interpret::Allocation::from_bytes_byte_aligned_immutable(bytes);
         let alloc = self.mk_const_alloc(alloc);
-        self.reserve_and_set_memory_alloc(alloc)
+        self.reserve_and_set_memory_dedup(alloc)
     }
 
     /// Returns a range of the start/end indices specified with the