[llvm-branch-commits] [mlir] [MLIR][OpenMP] Introduce the LoopWrapperInterface (PR #87232)

[Michael Kruse via llvm-branch-commits]

================
@@ -69,6 +69,74 @@ def ReductionClauseInterface : OpInterface<"ReductionClauseInterface"> {
   ];
 }
 
+def LoopWrapperInterface : OpInterface<"LoopWrapperInterface"> {
+  let description = [{
+    OpenMP operations that can wrap a single loop nest. When taking a wrapper
+    role, these operations must only contain a single region with a single block
+    in which there's a single operation and a terminator. That nested operation
+    must be another loop wrapper or an `omp.loop_nest`.
+  }];
+
+  let cppNamespace = "::mlir::omp";
+
+  let methods = [
+    InterfaceMethod<
+      /*description=*/[{
+        Tell whether the operation could be taking the role of a loop wrapper.
+        That is, it has a single region with a single block in which there are
+        two operations: another wrapper or `omp.loop_nest` operation and a
+        terminator.
+      }],
+      /*retTy=*/"bool",
+      /*methodName=*/"isWrapper",
+      (ins ), [{}], [{
+        if ($_op->getNumRegions() != 1)
+          return false;
+
+        ::mlir::Region &r = $_op->getRegion(0);
+        if (!r.hasOneBlock())
+          return false;
+
+        if (std::distance(r.op_begin(), r.op_end()) != 2)
+          return false;
+
+        ::mlir::Operation &firstOp = *r.op_begin();
+        ::mlir::Operation &secondOp = *(++r.op_begin());
----------------
Meinersbur wrote:

[serious]
```suggestion
        ::mlir::Operation &secondOp = *(std::next(r.op_begin()));
```
`++` would potentially modify the underlying iterator. I think it's a temporary here, but there is also no reason to modify a temporary.

Also, why not `r.op_begin()[0]` and `r.op_begin()[1]`?

https://github.com/llvm/llvm-project/pull/87232