Rollup merge of rust-lang#133861 - shamb0:refactor_InterpCx_allocate_str, r=RalfJung

Add allocate_bytes and refactor allocate_str in InterpCx for raw byte…

Fixes rust-lang/miri#4025

This PR introduces a new `allocate_bytes` function in InterpCx and refactors `allocate_str` to use it internally. This change improves memory allocation handling in the interpreter by:

1. Adding `allocate_bytes`:
   - Direct byte slice allocation support
   - Handles both mutable and immutable allocations
   - Maintains proper memory alignment and deduplication

2. Refactoring `allocate_str`:
   - Now uses `allocate_bytes` internally
   - Adds string-specific metadata handling
   - Preserves existing string allocation behavior

This is part 1 of the planned changes to improve timezone string handling in Miri. A follow-up PR will update Miri's timezone logic to use this new allocation mechanism.

Related: rust-lang/miri#4069

Author: matthiaskrgr

compiler/rustc_const_eval/src/interpret/place.rs

@@ -1018,29 +1018,48 @@ where
         self.allocate_dyn(layout, kind, MemPlaceMeta::None)
     }
 
-    /// Returns a wide MPlace of type `str` to a new 1-aligned allocation.
-    /// Immutable strings are deduplicated and stored in global memory.
-    pub fn allocate_str(
+    /// Allocates a sequence of bytes in the interpreter's memory.
+    /// For immutable allocations, uses deduplication to reuse existing memory.
+    /// For mutable allocations, creates a new unique allocation.
+    pub fn allocate_bytes(
         &mut self,
-        str: &str,
+        bytes: &[u8],
+        align: Align,
         kind: MemoryKind<M::MemoryKind>,
         mutbl: Mutability,
-    ) -> InterpResult<'tcx, MPlaceTy<'tcx, M::Provenance>> {
-        let tcx = self.tcx.tcx;
-
+    ) -> InterpResult<'tcx, Pointer<M::Provenance>> {
         // Use cache for immutable strings.
-        let ptr = if mutbl.is_not() {
+        if mutbl.is_not() {
             // Use dedup'd allocation function.
             let salt = M::get_global_alloc_salt(self, None);
-            let id = tcx.allocate_bytes_dedup(str.as_bytes(), salt);
+            let id = self.tcx.allocate_bytes_dedup(bytes, salt);
 
             // 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))?
+            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);
+            // Allocate new memory for mutable data.
+            self.allocate_bytes_ptr(bytes, align, kind, mutbl)
+        }
+    }
+
+    /// Allocates a string in the interpreter's memory with metadata for length.
+    /// Uses `allocate_bytes` internally but adds string-specific metadata handling.
+    pub fn allocate_str(
+        &mut self,
+        str: &str,
+        kind: MemoryKind<M::MemoryKind>,
+        mutbl: Mutability,
+    ) -> InterpResult<'tcx, MPlaceTy<'tcx, M::Provenance>> {
+        let bytes = str.as_bytes();
+        let ptr = self.allocate_bytes(bytes, Align::ONE, kind, mutbl)?;
+
+        // Create length metadata for the string.
+        let meta = Scalar::from_target_usize(u64::try_from(bytes.len()).unwrap(), self);
+
+        // Get layout for Rust's str type.
         let layout = self.layout_of(self.tcx.types.str_).unwrap();
+
+        // Combine pointer and metadata into a wide pointer.
         interp_ok(self.ptr_with_meta_to_mplace(
             ptr.into(),
             MemPlaceMeta::Meta(meta),