[clang] [llvm] [BPF] Add load-acquire and store-release instructions under -mcpu=v4 (PR #108636)

[Peilin Ye via cfe-commits]

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@@ -703,6 +715,39 @@ SDValue BPFTargetLowering::LowerSELECT_CC(SDValue Op, SelectionDAG &DAG) const {
   return DAG.getNode(BPFISD::SELECT_CC, DL, VTs, Ops);
 }
 
+SDValue BPFTargetLowering::LowerATOMIC_LOAD(SDValue Op,
+                                            SelectionDAG &DAG) const {
+  const char *Msg =
+      "sequentially consistent (seq_cst) atomic load is not supported";
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peilin-ye wrote:

Thanks for taking a look at this!
- - -
> Just pass this directly without the message variable?

Then after `git clang-format` it would look like:
```c
  if (cast<AtomicSDNode>(N)->getMergedOrdering() ==
      AtomicOrdering::SequentiallyConsistent)
    fail(DL, DAG,
         "sequentially consistent (seq_cst) atomic store is not supported");
```
I'd prefer keeping it as-is.

https://github.com/llvm/llvm-project/pull/108636