Rollup merge of rust-lang#140660 - RalfJung:more-order, r=WaffleLapkin

remove 'unordered' atomic intrinsics

As their doc comment already indicates, these operations do not currently have a place in our memory model. The intrinsics were introduced to support a hack in compiler-builtins, but that hack recently got removed (see rust-lang/compiler-builtins#788).

Author: Zalathar

compiler/rustc_codegen_gcc/src/builder.rs

@@ -2454,7 +2454,6 @@ impl ToGccOrdering for AtomicOrdering {
         use MemOrdering::*;
 
         let ordering = match self {
-            AtomicOrdering::Unordered => __ATOMIC_RELAXED,
             AtomicOrdering::Relaxed => __ATOMIC_RELAXED, // TODO(antoyo): check if that's the same.
             AtomicOrdering::Acquire => __ATOMIC_ACQUIRE,
             AtomicOrdering::Release => __ATOMIC_RELEASE,

compiler/rustc_codegen_llvm/src/llvm/ffi.rs

@@ -415,6 +415,7 @@ impl AtomicRmwBinOp {
 pub(crate) enum AtomicOrdering {
     #[allow(dead_code)]
     NotAtomic = 0,
+    #[allow(dead_code)]
     Unordered = 1,
     Monotonic = 2,
     // Consume = 3,  // Not specified yet.
@@ -428,7 +429,6 @@ impl AtomicOrdering {
     pub(crate) fn from_generic(ao: rustc_codegen_ssa::common::AtomicOrdering) -> Self {
         use rustc_codegen_ssa::common::AtomicOrdering as Common;
         match ao {
-            Common::Unordered => Self::Unordered,
             Common::Relaxed => Self::Monotonic,
             Common::Acquire => Self::Acquire,
             Common::Release => Self::Release,

compiler/rustc_codegen_ssa/src/common.rs

@@ -61,7 +61,6 @@ pub enum AtomicRmwBinOp {
 
 #[derive(Copy, Clone, Debug)]
 pub enum AtomicOrdering {
-    Unordered,
     Relaxed,
     Acquire,
     Release,

compiler/rustc_codegen_ssa/src/mir/intrinsic.rs

@@ -336,7 +336,6 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
                 };
 
                 let parse_ordering = |bx: &Bx, s| match s {
-                    "unordered" => Unordered,
                     "relaxed" => Relaxed,
                     "acquire" => Acquire,
                     "release" => Release,

library/core/src/intrinsics/mod.rs

@@ -430,12 +430,6 @@ pub unsafe fn atomic_load_acquire<T: Copy>(src: *const T) -> T;
 #[rustc_intrinsic]
 #[rustc_nounwind]
 pub unsafe fn atomic_load_relaxed<T: Copy>(src: *const T) -> T;
-/// Do NOT use this intrinsic; "unordered" operations do not exist in our memory model!
-/// In terms of the Rust Abstract Machine, this operation is equivalent to `src.read()`,
-/// i.e., it performs a non-atomic read.
-#[rustc_intrinsic]
-#[rustc_nounwind]
-pub unsafe fn atomic_load_unordered<T: Copy>(src: *const T) -> T;
 
 /// Stores the value at the specified memory location.
 /// `T` must be an integer or pointer type.
@@ -464,12 +458,6 @@ pub unsafe fn atomic_store_release<T: Copy>(dst: *mut T, val: T);
 #[rustc_intrinsic]
 #[rustc_nounwind]
 pub unsafe fn atomic_store_relaxed<T: Copy>(dst: *mut T, val: T);
-/// Do NOT use this intrinsic; "unordered" operations do not exist in our memory model!
-/// In terms of the Rust Abstract Machine, this operation is equivalent to `dst.write(val)`,
-/// i.e., it performs a non-atomic write.
-#[rustc_intrinsic]
-#[rustc_nounwind]
-pub unsafe fn atomic_store_unordered<T: Copy>(dst: *mut T, val: T);
 
 /// Stores the value at the specified memory location, returning the old value.
 /// `T` must be an integer or pointer type.