Rollup merge of rust-lang#84905 - RalfJung:copy, r=oli-obk

CTFE engine: rename copy → copy_intrinsic, move to intrinsics.rs

The `copy` name is confusing for this function because we also have `copy_op` which is pretty different. I hope `copy_intrinsic` is clearer. Also `step.rs` should really just contain the main loop and opcode dispatch, so move this helper function to a more appropriate place.

r? ```@oli-obk```

compiler/rustc_mir/src/interpret/intrinsics.rs

@@ -323,7 +323,7 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
                 self.write_scalar(result, dest)?;
             }
             sym::copy => {
-                self.copy(&args[0], &args[1], &args[2], /*nonoverlapping*/ false)?;
+                self.copy_intrinsic(&args[0], &args[1], &args[2], /*nonoverlapping*/ false)?;
             }
             sym::offset => {
                 let ptr = self.read_scalar(&args[0])?.check_init()?;
@@ -530,4 +530,36 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
         )?;
         Ok(offset_ptr)
     }
+
+    /// Copy `count*size_of::<T>()` many bytes from `*src` to `*dst`.
+    pub(crate) fn copy_intrinsic(
+        &mut self,
+        src: &OpTy<'tcx, <M as Machine<'mir, 'tcx>>::PointerTag>,
+        dst: &OpTy<'tcx, <M as Machine<'mir, 'tcx>>::PointerTag>,
+        count: &OpTy<'tcx, <M as Machine<'mir, 'tcx>>::PointerTag>,
+        nonoverlapping: bool,
+    ) -> InterpResult<'tcx> {
+        let count = self.read_scalar(&count)?.to_machine_usize(self)?;
+        let layout = self.layout_of(src.layout.ty.builtin_deref(true).unwrap().ty)?;
+        let (size, align) = (layout.size, layout.align.abi);
+        let size = size.checked_mul(count, self).ok_or_else(|| {
+            err_ub_format!(
+                "overflow computing total size of `{}`",
+                if nonoverlapping { "copy_nonoverlapping" } else { "copy" }
+            )
+        })?;
+
+        // Make sure we check both pointers for an access of the total size and aligment,
+        // *even if* the total size is 0.
+        let src =
+            self.memory.check_ptr_access(self.read_scalar(&src)?.check_init()?, size, align)?;
+
+        let dst =
+            self.memory.check_ptr_access(self.read_scalar(&dst)?.check_init()?, size, align)?;
+
+        if let (Some(src), Some(dst)) = (src, dst) {
+            self.memory.copy(src, dst, size, nonoverlapping)?;
+        }
+        Ok(())
+    }
 }

compiler/rustc_mir/src/interpret/step.rs

@@ -2,7 +2,6 @@
 //!
 //! The main entry point is the `step` method.
 
-use crate::interpret::OpTy;
 use rustc_middle::mir;
 use rustc_middle::mir::interpret::{InterpResult, Scalar};
 use rustc_target::abi::LayoutOf;
@@ -119,7 +118,7 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
                 let src = self.eval_operand(src, None)?;
                 let dst = self.eval_operand(dst, None)?;
                 let count = self.eval_operand(count, None)?;
-                self.copy(&src, &dst, &count, /* nonoverlapping */ true)?;
+                self.copy_intrinsic(&src, &dst, &count, /* nonoverlapping */ true)?;
             }
 
             // Statements we do not track.
@@ -149,37 +148,6 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
         Ok(())
     }
 
-    pub(crate) fn copy(
-        &mut self,
-        src: &OpTy<'tcx, <M as Machine<'mir, 'tcx>>::PointerTag>,
-        dst: &OpTy<'tcx, <M as Machine<'mir, 'tcx>>::PointerTag>,
-        count: &OpTy<'tcx, <M as Machine<'mir, 'tcx>>::PointerTag>,
-        nonoverlapping: bool,
-    ) -> InterpResult<'tcx> {
-        let count = self.read_scalar(&count)?.to_machine_usize(self)?;
-        let layout = self.layout_of(src.layout.ty.builtin_deref(true).unwrap().ty)?;
-        let (size, align) = (layout.size, layout.align.abi);
-        let size = size.checked_mul(count, self).ok_or_else(|| {
-            err_ub_format!(
-                "overflow computing total size of `{}`",
-                if nonoverlapping { "copy_nonoverlapping" } else { "copy" }
-            )
-        })?;
-
-        // Make sure we check both pointers for an access of the total size and aligment,
-        // *even if* the total size is 0.
-        let src =
-            self.memory.check_ptr_access(self.read_scalar(&src)?.check_init()?, size, align)?;
-
-        let dst =
-            self.memory.check_ptr_access(self.read_scalar(&dst)?.check_init()?, size, align)?;
-
-        if let (Some(src), Some(dst)) = (src, dst) {
-            self.memory.copy(src, dst, size, nonoverlapping)?;
-        }
-        Ok(())
-    }
-
     /// Evaluate an assignment statement.
     ///
     /// There is no separate `eval_rvalue` function. Instead, the code for handling each rvalue