[clang] [CIR] Add offload container Op (PR #206576)

[Steffen Larsen via cfe-commits]

================
@@ -110,6 +111,112 @@ Operation *cir::CIRDialect::materializeConstant(mlir::OpBuilder &builder,
                                  mlir::cast<mlir::TypedAttr>(value));
 }
 
+//===----------------------------------------------------------------------===//
+// Offload container helpers
+//===----------------------------------------------------------------------===//
+
+bool cir::isOffloadContainer(mlir::ModuleOp module) {
+  return module->hasAttr(cir::CIRDialect::getOffloadContainerAttrName());
+}
+
+mlir::ModuleOp cir::getOffloadHostModule(mlir::ModuleOp container) {
+  assert(isOffloadContainer(container) && "expected an offload container");
+  return mlir::cast<mlir::ModuleOp>(container.getBody()->front());
+}
+
+llvm::iterator_range<mlir::Block::op_iterator<mlir::ModuleOp>>
+cir::getOffloadDeviceModules(mlir::ModuleOp container) {
+  assert(isOffloadContainer(container) && "expected an offload container");
+  mlir::Block &body = *container.getBody();
+  auto begin = body.op_begin<mlir::ModuleOp>();
+  auto end = body.op_end<mlir::ModuleOp>();
+  if (begin != end)
+    ++begin;
+  return {begin, end};
----------------
steffenlarsen wrote:

Since verification requires containers to be non-empty, the branching here seems redundant to me.

```suggestion
  return {body.op_begin<mlir::ModuleOp>() + 1, body.op_end<mlir::ModuleOp>()};
```
If we want to be sure, we could have an assert checking that it is non-empty. If so, it might also make sense to add to `getOffloadHostModule`.

https://github.com/llvm/llvm-project/pull/206576