[clang] [CIR] Upstream handling for __builtin_prefetch (PR #164387)

[Andy Kaylor via cfe-commits]

================
@@ -4049,6 +4049,39 @@ def CIR_ExpectOp : CIR_Op<"expect", [
   }];
 }
 
+//===----------------------------------------------------------------------===//
+// PrefetchOp
+//===----------------------------------------------------------------------===//
+
+def CIR_PrefetchOp : CIR_Op<"prefetch"> {
+  let summary = "prefetch operation";
+  let description = [{
+    The `cir.prefetch` op prefetches data from the memmory address.
+
+    ```mlir
+    cir.prefetch(%0 : !cir.ptr<!void>) locality(1) write
+    ```
+
+    This opcode has the three attributes:
+    1. The $locality is a temporal locality specifier
+    ranging from (0) - no locality, to (3) - extremely local keep in cache.
+    2. The $isWrite is the specifier determining if the prefetch is prepaired
+    for a 'read' or 'write'.
----------------
andykaylor wrote:

```suggestion

    $isWrite specifies whether the prefetch is for a 'read' or 'write'.
```
I'm also suggesting an empty line here for readability.

https://github.com/llvm/llvm-project/pull/164387