[llvm] [Offload] Introduce ATTACH map-type support for pointer attachment. (PR #149036)

[Abhinav Gaba via llvm-commits]

================
@@ -821,19 +821,22 @@ int processAttachEntries(DeviceTy &Device, AttachInfoTy &AttachInfo,
       return TPR;
     };
 
-    // Get device version of the pointer (e.g., &p)
+    // Get device version of the pointee (e.g., &p[10]) first, as we can
+    // release its TPR after extracting the pointer value.
+    void *TgtPteeBegin;
+    if (auto PteeTPROpt = LookupTargetPointer(HstPteeBegin, 0, "pointee"))
+      TgtPteeBegin = PteeTPROpt->TargetPointer;
+    else
+      continue;
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abhinavgaba wrote:

It's written this way to make sure that the scope of `PteeTPROpt` is limited to the `if` statement. That way the TPR gets destroyed as soon as we get out of the `if`, and releases the lock it had acquired on the map-entry.

Another alternative would be:

```cpp
void *TgtPteeBegin;
{
  auto PteeTPROpt = LookupTargetPointer(HstPteeBegin, 0, "pointee");
  if (!PteeTPROpt)
    TgtPteeBegin = PteeTPROpt->TargetPointer;
}
```
Otherwise, if we want to keep the original way it was written, as you suggested, we would need to explicitly call `PteeTPROpt->reset()` to release the lock.

```cpp
  auto PteeTPROpt = LookupTargetPointer(HstPteeBegin, 0, "pointee");
  if (!PteeTPROpt)
    continue;
  void *TgtPteeBegin = PteeTPROpt->TargetPointer;
  PteeTPROpt->reset();
```


https://github.com/llvm/llvm-project/pull/149036