Rollup merge of #141507 - RalfJung:atomic-intrinsics, r=bjorn3

atomic_load intrinsic: use const generic parameter for ordering

We have a gazillion intrinsics for the atomics because we encode the ordering into the intrinsic name rather than making it a parameter. This is particularly bad for those operations that take two orderings. Let's fix that!

This PR only converts `load`, to see if there's any feedback that would fundamentally change the strategy we pursue for the const generic intrinsics.

The first two commits are preparation and could be a separate PR if you prefer.

`@BoxyUwU` -- I hope this is a use of const generics that is unlikely to explode? All we need is a const generic of enum type. We could funnel it through an integer if we had to but an enum is obviously nicer...

`@bjorn3` it seems like the cranelift backend entirely ignores the ordering?

Author: matthiaskrgr

src/builder.rs

@@ -12,7 +12,7 @@ use rustc_abi::{Align, HasDataLayout, Size, TargetDataLayout, WrappingRange};
 use rustc_apfloat::{Float, Round, Status, ieee};
 use rustc_codegen_ssa::MemFlags;
 use rustc_codegen_ssa::common::{
-    AtomicOrdering, AtomicRmwBinOp, IntPredicate, RealPredicate, SynchronizationScope, TypeKind,
+    AtomicRmwBinOp, IntPredicate, RealPredicate, SynchronizationScope, TypeKind,
 };
 use rustc_codegen_ssa::mir::operand::{OperandRef, OperandValue};
 use rustc_codegen_ssa::mir::place::PlaceRef;
@@ -26,7 +26,7 @@ use rustc_middle::middle::codegen_fn_attrs::CodegenFnAttrs;
 use rustc_middle::ty::layout::{
     FnAbiError, FnAbiOfHelpers, FnAbiRequest, HasTyCtxt, HasTypingEnv, LayoutError, LayoutOfHelpers,
 };
-use rustc_middle::ty::{self, Instance, Ty, TyCtxt};
+use rustc_middle::ty::{self, AtomicOrdering, Instance, Ty, TyCtxt};
 use rustc_span::Span;
 use rustc_span::def_id::DefId;
 use rustc_target::callconv::FnAbi;
@@ -75,7 +75,7 @@ impl<'a, 'gcc, 'tcx> Builder<'a, 'gcc, 'tcx> {
 
         let load_ordering = match order {
             // TODO(antoyo): does this make sense?
-            AtomicOrdering::AcquireRelease | AtomicOrdering::Release => AtomicOrdering::Acquire,
+            AtomicOrdering::AcqRel | AtomicOrdering::Release => AtomicOrdering::Acquire,
             _ => order,
         };
         let previous_value =
@@ -2474,8 +2474,8 @@ impl ToGccOrdering for AtomicOrdering {
             AtomicOrdering::Relaxed => __ATOMIC_RELAXED, // TODO(antoyo): check if that's the same.
             AtomicOrdering::Acquire => __ATOMIC_ACQUIRE,
             AtomicOrdering::Release => __ATOMIC_RELEASE,
-            AtomicOrdering::AcquireRelease => __ATOMIC_ACQ_REL,
-            AtomicOrdering::SequentiallyConsistent => __ATOMIC_SEQ_CST,
+            AtomicOrdering::AcqRel => __ATOMIC_ACQ_REL,
+            AtomicOrdering::SeqCst => __ATOMIC_SEQ_CST,
         };
         ordering as i32
     }