[flang-commits] [flang] [Flang] Add FIR and LLVM lowering support for prefetch directive (PR #167272)

[Tom Eccles via flang-commits]

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@@ -353,6 +351,39 @@ def fir_StoreOp : fir_Op<"store", [FirAliasTagOpInterface,
   }];
 }
 
+def fir_PrefetchOp : fir_Op<"prefetch", []> {
+  let summary = "prefetch a memory reference";
+
+  let description = [{
+    The prefetch is a hint to the code generator that the memory reference will
+    be used in the near future. The prefetch is not guaranteed to be executed.
+
+    ```
+      %a = ... -> !fir.ref<i32>
+      fir.prefetch %a {read, data, localityHint = 3 : i32} : !fir.ref<i32>
+      // ...
+      fir.load %a : !fir.ref<i32> // use the prefetched value
+    ```
+  }];
+
+  /// `memref' is the address to be prefetched
+  /// `rw'          : rw specifier >
+  ///                  read is 0 (default), write is 1
+  /// `localityHint': temporal locality specifier >
+  ///                  value ranging from 0 - no locality to 3 - extremely local
+  /// `cacheType'   : cache type specifier >
+  ///                  instruction cache is 0, data cache is 1 (default)
+  /// NOTE: The numerical values used here is in reference to the LLVM LangRef
+  let arguments =
+      (ins Arg<AnyReferenceLike,
+               "prefetch memory address", [MemWrite]> : $memref,
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tblah wrote:

I think this should be modelled as a read rather than a write because that is closer to what it actually does. A write could prevent some optimisations.

https://github.com/llvm/llvm-project/pull/167272