[clang] [OpenACC][CIR] Implement 'alloca copying' for private lowering (PR #161382)

[Andy Kaylor via cfe-commits]

================
@@ -36,6 +36,77 @@ mlir::Block *OpenACCRecipeBuilderBase::createRecipeBlock(mlir::Region &region,
   llvm::SmallVector<mlir::Location> locs{types.size(), loc};
   return builder.createBlock(&region, region.end(), types, locs);
 }
+void OpenACCRecipeBuilderBase::makeAllocaCopy(mlir::Location loc,
+                                              mlir::Type copyType,
+                                              mlir::Value numEltsToCopy,
+                                              mlir::Value offsetPerSubarray,
+                                              mlir::Value destAlloca,
+                                              mlir::Value srcAlloca) {
+  mlir::OpBuilder::InsertionGuard guardCase(builder);
+
+  mlir::Type itrTy = cgf.cgm.convertType(cgf.getContext().UnsignedLongLongTy);
+  auto itrPtrTy = cir::PointerType::get(itrTy);
+  mlir::IntegerAttr itrAlign =
+      cgf.cgm.getSize(cgf.getContext().getTypeAlignInChars(
+          cgf.getContext().UnsignedLongLongTy));
+
+  auto loopBuilder = [&]() {
+    auto itr =
+        cir::AllocaOp::create(builder, loc, itrPtrTy, itrTy, "itr", itrAlign);
+    cir::ConstantOp constZero = builder.getConstInt(loc, itrTy, 0);
+    builder.CIRBaseBuilderTy::createStore(loc, constZero.getResult(), itr);
+    builder.createFor(
+        loc,
+        /*condBuilder=*/
+        [&](mlir::OpBuilder &b, mlir::Location loc) {
+          // itr < numEltsToCopy
+          // Enforce a trip count of 1 if there wasn't any element count, this
+          // way we can just use this loop with a constant bounds instead of a
+          // separate code path.
+          if (!numEltsToCopy)
+            numEltsToCopy = builder.getConstInt(loc, itrTy, 1).getResult();
----------------
andykaylor wrote:

```suggestion
            numEltsToCopy = builder.getConstInt(loc, itrTy, 1);
```

https://github.com/llvm/llvm-project/pull/161382