make internal comment more precise

Author: RalfJung

compiler/rustc_codegen_ssa/src/mir/rvalue.rs

@@ -361,12 +361,16 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
             (Int(..) | Float(_), Int(..) | Float(_)) => bx.bitcast(imm, to_backend_ty),
             (Pointer(..), Pointer(..)) => bx.pointercast(imm, to_backend_ty),
             (Int(..), Pointer(..)) => bx.ptradd(bx.const_null(bx.type_ptr()), imm),
-            (Pointer(..), Int(..)) => bx.ptrtoint(imm, to_backend_ty),
+            (Pointer(..), Int(..)) => {
+                // FIXME: this exposes the provenance, which shouldn't be necessary.
+                bx.ptrtoint(imm, to_backend_ty)
+            }
             (Float(_), Pointer(..)) => {
                 let int_imm = bx.bitcast(imm, bx.cx().type_isize());
                 bx.ptradd(bx.const_null(bx.type_ptr()), int_imm)
             }
             (Pointer(..), Float(_)) => {
+                // FIXME: this exposes the provenance, which shouldn't be necessary.
                 let int_imm = bx.ptrtoint(imm, bx.cx().type_isize());
                 bx.bitcast(int_imm, to_backend_ty)
             }

library/core/src/ptr/const_ptr.rs

@@ -192,13 +192,12 @@ impl<T: ?Sized> *const T {
     #[inline]
     #[stable(feature = "strict_provenance", since = "CURRENT_RUSTC_VERSION")]
     pub fn with_addr(self, addr: usize) -> Self {
-        // This should probably be an intrinsic to make it more efficient, but meanwhile, we can
-        // implement it with `wrapping_offset`, which preserves the pointer's provenance.
+        // This should probably be an intrinsic to avoid doing any sort of arithmetic, but
+        // meanwhile, we can implement it with `wrapping_offset`, which preserves the pointer's
+        // provenance.
         let self_addr = self.addr() as isize;
         let dest_addr = addr as isize;
         let offset = dest_addr.wrapping_sub(self_addr);
-
-        // This is the canonical desugaring of this operation
         self.wrapping_byte_offset(offset)
     }
 

library/core/src/ptr/mut_ptr.rs

@@ -179,13 +179,12 @@ impl<T: ?Sized> *mut T {
     #[inline]
     #[stable(feature = "strict_provenance", since = "CURRENT_RUSTC_VERSION")]
     pub fn with_addr(self, addr: usize) -> Self {
-        // This should probably be an intrinsic to make it more efficient, but meanwhile, we can
-        // implement it with `wrapping_offset`, which preserves the pointer's provenance.
+        // This should probably be an intrinsic to avoid doing any sort of arithmetic, but
+        // meanwhile, we can implement it with `wrapping_offset`, which preserves the pointer's
+        // provenance.
         let self_addr = self.addr() as isize;
         let dest_addr = addr as isize;
         let offset = dest_addr.wrapping_sub(self_addr);
-
-        // This is the canonical desugaring of this operation
         self.wrapping_byte_offset(offset)
     }