Addresses comments in PR #43836

- removes warnings introduced in changeset 0cd3587
- makes documentation more neat and grammatically correct

src/libcore/ptr.rs

@@ -384,11 +384,10 @@ pub unsafe fn write_unaligned<T>(dst: *mut T, src: T) {
 /// over time. That being said, the semantics will almost always end up pretty
 /// similar to [C11's definition of volatile][c11].
 ///
-/// Compiler shouldn't change relative order or number of volatile memory
+/// The compiler shouldn't change the relative order or number of volatile
-/// operations, however this implies that memory operation actually takes place.
+/// memory operations. However, volatile memory operations on zero-sized types
-/// If a zero-sized type is used in a specialisation of `read_volatile`, value
+/// (e.g. if a zero-sized type is passed to `read_volatile`) are no-ops
-/// is known at any time and can not be modified outside of program control.
+/// and may be ignored.
-/// In this case such operation may be omitted by compiler backend.
 ///
 /// [c11]: http://www.open-std.org/jtc1/sc22/wg14/www/docs/n1570.pdf
 ///
@@ -433,11 +432,10 @@ pub unsafe fn read_volatile<T>(src: *const T) -> T {
 /// over time. That being said, the semantics will almost always end up pretty
 /// similar to [C11's definition of volatile][c11].
 ///
-/// Compiler shouldn't change relative order or number of volatile memory
+/// The compiler shouldn't change the relative order or number of volatile
-/// operations, however this implies that memory operation actually takes place.
+/// memory operations. However, volatile memory operations on zero-sized types
-/// If a zero-sized type is used in a specialisation of `write_volatile`, value
+/// (e.g. if a zero-sized type is passed to `write_volatile`) are no-ops
-/// is known at any time and can not be modified outside of program control.
+/// and may be ignored.
-/// In this case such operation may be omitted by compiler backend.
 ///
 /// [c11]: http://www.open-std.org/jtc1/sc22/wg14/www/docs/n1570.pdf
 ///

src/librustc_trans/intrinsic.rs

@@ -83,38 +83,6 @@ fn get_simple_intrinsic(ccx: &CrateContext, name: &str) -> Option<ValueRef> {
     Some(ccx.get_intrinsic(&llvm_name))
 }
 
-fn warn_if_size_is_weird<'a, 'tcx>(bcx: &Builder<'a, 'tcx>,
-                                   tp_ty: Ty<'tcx>,
-                                   count: ValueRef,
-                                   span: Span,
-                                   name: &str) {
-    let ccx = bcx.ccx;
-    let lltp_ty = type_of::type_of(ccx, tp_ty);
-    let ty_size = machine::llsize_of(ccx, lltp_ty);
-    let total = const_to_uint( bcx.mul(ty_size, count) );
-
-    if total > 0 {
-        return;
-    }
-
-    let text = format!("suspicious monomorphization of `{}` intrinsic", name);
-    let note = match name
-    {
-        "volatile_load" | "volatile_store" =>
-             format!("'{}' was specialized with zero-sized type '{}'",
-                    name, tp_ty),
-        _ => format!("'{}' was specialized with type '{}', number of \
-                     elements is {}",
-                     name, tp_ty,
-                     const_to_uint(count))
-    };
-
-    let sess = bcx.sess();
-    sess.struct_span_warn(span, &text)
-        .note(&note)
-        .emit();
-}
-
 /// Remember to add all intrinsics here, in librustc_typeck/check/mod.rs,
 /// and in libcore/intrinsics.rs; if you need access to any llvm intrinsics,
 /// add them to librustc_trans/trans/context.rs
@@ -249,24 +217,17 @@ pub fn trans_intrinsic_call<'a, 'tcx>(bcx: &Builder<'a, 'tcx>,
         }
 
         "volatile_copy_nonoverlapping_memory" => {
-            let tp_ty = substs.type_at(0);
+            copy_intrinsic(bcx, false, true, substs.type_at(0), llargs[0], llargs[1], llargs[2])
-            warn_if_size_is_weird(bcx, tp_ty, llargs[2], span, name);
-            copy_intrinsic(bcx, false, true, tp_ty, llargs[0], llargs[1], llargs[2])
         }
         "volatile_copy_memory" => {
-            let tp_ty = substs.type_at(0);
+            copy_intrinsic(bcx, true, true, substs.type_at(0), llargs[0], llargs[1], llargs[2])
-            warn_if_size_is_weird(bcx, tp_ty, llargs[2], span, name);
-            copy_intrinsic(bcx, true, true, tp_ty, llargs[0], llargs[1], llargs[2])
         }
         "volatile_set_memory" => {
-            let tp_ty = substs.type_at(0);
+            memset_intrinsic(bcx, true, substs.type_at(0), llargs[0], llargs[1], llargs[2])
-            warn_if_size_is_weird(bcx, tp_ty, llargs[2], span, name);
-            memset_intrinsic(bcx, true, tp_ty, llargs[0], llargs[1], llargs[2])
         }
         "volatile_load" => {
             let tp_ty = substs.type_at(0);
             let mut ptr = llargs[0];
-            warn_if_size_is_weird(bcx, tp_ty, C_uint(ccx,1usize), span, name);
             if let Some(ty) = fn_ty.ret.cast {
                 ptr = bcx.pointercast(ptr, ty.ptr_to());
             }
@@ -278,7 +239,6 @@ pub fn trans_intrinsic_call<'a, 'tcx>(bcx: &Builder<'a, 'tcx>,
         },
         "volatile_store" => {
             let tp_ty = substs.type_at(0);
-            warn_if_size_is_weird(bcx, tp_ty, C_uint(ccx,1usize), span, name);
             if type_is_fat_ptr(bcx.ccx, tp_ty) {
                 bcx.volatile_store(llargs[1], get_dataptr(bcx, llargs[0]));
                 bcx.volatile_store(llargs[2], get_meta(bcx, llargs[0]));

src/test/run-pass/issue-39827.rs

@@ -13,6 +13,11 @@ use std::intrinsics::{ volatile_copy_memory, volatile_store, volatile_load,
                        volatile_copy_nonoverlapping_memory,
                        volatile_set_memory };
 
+//
+// This test ensures that volatile intrinsics can be specialised with
+// zero-sized types and, in case of copy/set functions, can accept
+// number of elements equal to zero.
+//
 fn main () {
     let mut dst_pair = (1, 2);
     let src_pair = (3, 4);

src/test/ui/issue-39827.stderr

@@ -1,73 +0,0 @@
-warning: suspicious monomorphization of `volatile_copy_memory` intrinsic
-  --> $DIR/issue-39827.rs:26:9
-   |
-26 |         volatile_copy_memory(&mut dst_pair, &dst_pair, COUNT_0);
-   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
-   |
-   = note: 'volatile_copy_memory' was specialized with type '(i32, i32)', number of elements is 0
-
-warning: suspicious monomorphization of `volatile_copy_nonoverlapping_memory` intrinsic
-  --> $DIR/issue-39827.rs:27:9
-   |
-27 |         volatile_copy_nonoverlapping_memory(&mut dst_pair, &src_pair, 0);
-   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
-   |
-   = note: 'volatile_copy_nonoverlapping_memory' was specialized with type '(i32, i32)', number of elements is 0
-
-warning: suspicious monomorphization of `volatile_copy_memory` intrinsic
-  --> $DIR/issue-39827.rs:28:9
-   |
-28 |         volatile_copy_memory(&mut dst_empty, &dst_empty, 100);
-   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
-   |
-   = note: 'volatile_copy_memory' was specialized with type '()', number of elements is 100
-
-warning: suspicious monomorphization of `volatile_copy_nonoverlapping_memory` intrinsic
-  --> $DIR/issue-39827.rs:29:9
-   |
-29 | /         volatile_copy_nonoverlapping_memory(&mut dst_empty, &src_empty,
-30 | |                                             COUNT_100);
-   | |______________________________________________________^
-   |
-   = note: 'volatile_copy_nonoverlapping_memory' was specialized with type '()', number of elements is 100
-
-warning: suspicious monomorphization of `volatile_set_memory` intrinsic
-  --> $DIR/issue-39827.rs:31:9
-   |
-31 |         volatile_set_memory(&mut dst_empty, 0, COUNT_100);
-   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
-   |
-   = note: 'volatile_set_memory' was specialized with type '()', number of elements is 100
-
-warning: suspicious monomorphization of `volatile_set_memory` intrinsic
-  --> $DIR/issue-39827.rs:32:9
-   |
-32 |         volatile_set_memory(&mut dst_pair, 0, COUNT_0);
-   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
-   |
-   = note: 'volatile_set_memory' was specialized with type '(i32, i32)', number of elements is 0
-
-warning: suspicious monomorphization of `volatile_store` intrinsic
-  --> $DIR/issue-39827.rs:33:9
-   |
-33 |         volatile_store(&mut dst_empty, ());
-   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
-   |
-   = note: 'volatile_store' was specialized with zero-sized type '()'
-
-warning: suspicious monomorphization of `volatile_store` intrinsic
-  --> $DIR/issue-39827.rs:34:9
-   |
-34 |         volatile_store(&mut dst_empty, src_empty);
-   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
-   |
-   = note: 'volatile_store' was specialized with zero-sized type '()'
-
-warning: suspicious monomorphization of `volatile_load` intrinsic
-  --> $DIR/issue-39827.rs:35:9
-   |
-35 |         volatile_load(&src_empty);
-   |         ^^^^^^^^^^^^^^^^^^^^^^^^^
-   |
-   = note: 'volatile_load' was specialized with zero-sized type '()'
-