Rollup merge of #147472 - AMS21:remove_llvm_rust_atomics, r=nikic

refactor: replace `LLVMRustAtomicLoad/Store` with LLVM built-in functions

This simplifies the code and reduces the burden of maintaining our own wrappers.

Work towards https://github.com/rust-lang/rust/issues/46437

compiler/rustc_codegen_llvm/src/builder.rs

@@ -639,13 +639,9 @@ impl<'a, 'll, 'tcx> BuilderMethods<'a, 'tcx> for Builder<'a, 'll, 'tcx> {
         size: Size,
     ) -> &'ll Value {
         unsafe {
-            let load = llvm::LLVMRustBuildAtomicLoad(
-                self.llbuilder,
-                ty,
-                ptr,
-                UNNAMED,
-                AtomicOrdering::from_generic(order),
-            );
+            let load = llvm::LLVMBuildLoad2(self.llbuilder, ty, ptr, UNNAMED);
+            // Set atomic ordering
+            llvm::LLVMSetOrdering(load, AtomicOrdering::from_generic(order));
             // LLVM requires the alignment of atomic loads to be at least the size of the type.
             llvm::LLVMSetAlignment(load, size.bytes() as c_uint);
             load
@@ -872,12 +868,9 @@ impl<'a, 'll, 'tcx> BuilderMethods<'a, 'tcx> for Builder<'a, 'll, 'tcx> {
         debug!("Store {:?} -> {:?}", val, ptr);
         assert_eq!(self.cx.type_kind(self.cx.val_ty(ptr)), TypeKind::Pointer);
         unsafe {
-            let store = llvm::LLVMRustBuildAtomicStore(
-                self.llbuilder,
-                val,
-                ptr,
-                AtomicOrdering::from_generic(order),
-            );
+            let store = llvm::LLVMBuildStore(self.llbuilder, val, ptr);
+            // Set atomic ordering
+            llvm::LLVMSetOrdering(store, AtomicOrdering::from_generic(order));
             // LLVM requires the alignment of atomic stores to be at least the size of the type.
             llvm::LLVMSetAlignment(store, size.bytes() as c_uint);
         }

compiler/rustc_codegen_llvm/src/llvm/ffi.rs

@@ -1151,6 +1151,7 @@ unsafe extern "C" {
 
     // Operations on load/store instructions (only)
     pub(crate) fn LLVMSetVolatile(MemoryAccessInst: &Value, volatile: Bool);
+    pub(crate) fn LLVMSetOrdering(MemoryAccessInst: &Value, Ordering: AtomicOrdering);
 
     // Operations on phi nodes
     pub(crate) fn LLVMAddIncoming<'a>(
@@ -2090,22 +2091,6 @@ unsafe extern "C" {
         RHS: &'a Value,
     ) -> &'a Value;
 
-    // Atomic Operations
-    pub(crate) fn LLVMRustBuildAtomicLoad<'a>(
-        B: &Builder<'a>,
-        ElementType: &'a Type,
-        PointerVal: &'a Value,
-        Name: *const c_char,
-        Order: AtomicOrdering,
-    ) -> &'a Value;
-
-    pub(crate) fn LLVMRustBuildAtomicStore<'a>(
-        B: &Builder<'a>,
-        Val: &'a Value,
-        Ptr: &'a Value,
-        Order: AtomicOrdering,
-    ) -> &'a Value;
-
     pub(crate) fn LLVMRustTimeTraceProfilerInitialize();
 
     pub(crate) fn LLVMRustTimeTraceProfilerFinishThread();