use CheckInAllocMsg::PointerArithmeticTest for ptr_offset error

compiler/rustc_mir/src/interpret/intrinsics.rs

@@ -526,7 +526,7 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
             min_ptr,
             Size::from_bytes(size),
             None,
-            CheckInAllocMsg::InboundsTest,
+            CheckInAllocMsg::PointerArithmeticTest,
         )?;
         Ok(offset_ptr)
     }

compiler/rustc_mir/src/interpret/machine.rs

@@ -369,6 +369,7 @@ pub trait Machine<'mir, 'tcx>: Sized {
     ) -> InterpResult<'tcx, Pointer<Self::PointerTag>> {
         Err((if int == 0 {
             // This is UB, seriously.
+            // (`DanglingIntPointer` with these exact arguments has special printing code.)
             err_ub!(DanglingIntPointer(0, CheckInAllocMsg::InboundsTest))
         } else {
             // This is just something we cannot support during const-eval.

compiler/rustc_mir/src/interpret/validity.rs

@@ -330,7 +330,7 @@ impl<'rt, 'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> ValidityVisitor<'rt, 'mir, '
                         vtable,
                         3 * self.ecx.tcx.data_layout.pointer_size, // drop, size, align
                         Some(self.ecx.tcx.data_layout.pointer_align.abi),
-                        CheckInAllocMsg::InboundsTest,
+                        CheckInAllocMsg::InboundsTest, // will anyway be replaced by validity message
                     ),
                     self.path,
                     err_ub!(DanglingIntPointer(..)) |
@@ -416,7 +416,7 @@ impl<'rt, 'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> ValidityVisitor<'rt, 'mir, '
                 place.ptr,
                 size,
                 Some(align),
-                CheckInAllocMsg::InboundsTest,
+                CheckInAllocMsg::InboundsTest, // will anyway be replaced by validity message
             ),
             self.path,
             err_ub!(AlignmentCheckFailed { required, has }) =>