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

[Andy Kaylor via cfe-commits]

================
@@ -125,14 +200,21 @@ mlir::Value OpenACCRecipeBuilderBase::makeBoundsAlloca(
 
       mlir::Type eltTy = cgf.convertType(resultType);
       cir::PointerType ptrTy = builder.getPointerTo(eltTy);
-      builder.createAlloca(loc, ptrTy, eltTy, "openacc.init.bounds",
-                           cgf.getContext().getTypeAlignInChars(resultType),
-                           curSize);
-
-      // TODO: OpenACC : At this point we should be copying the addresses of
-      // each element of this to the last allocation.  At the moment, that is
-      // not yet implemented.
-      cgf.cgm.errorNYI(exprRange, "OpenACC recipe alloca copying");
+      mlir::Value curAlloca = builder.createAlloca(
+          loc, ptrTy, eltTy, "openacc.init.bounds",
+          cgf.getContext().getTypeAlignInChars(resultType), curSize);
+
+      makeAllocaCopy(loc, ptrTy, cumulativeElts, eltsPerSubArray, lastAlloca,
+                     curAlloca);
+      lastAlloca = curAlloca;
+    } else {
+      // In the case of an array, we just need to decay the pointer, so just do
+      // a zero-offset stride on the last alloca to decay it down an array
+      // level.
+      cir::ConstantOp constZero = builder.getConstInt(loc, itrTy, 0);
+      lastAlloca = builder.getArrayElement(
+          loc, loc, lastAlloca, cgf.convertType(resultType),
+          constZero.getResult(), /*shouldDecay=*/true);
----------------
andykaylor wrote:

```suggestion
          constZero, /*shouldDecay=*/true);
```

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