[flang-commits] [flang] Skip POINTER components in implicit mapper generation (PR #177848)

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agozillon wrote:

Thank you, that runtime trace looks fine to me, it's only mapping the data for arr from what I can see at least. So it's a bit odd it magically has the data on the device to do what it's doing here. However, if NVIDIA GPUs are anything like AMDs then there is possibly something like USM or XNACK (address translation not acknowledged) at play, the former obviously having unified memory so technically the data is always available, the latter being something that will effectively move the data if it is not available at time of checking, so effectively moving the data to device for you. For AMD either of these would pop up in the OpenMP runtime trace as active, but I don't know if it'd do that for NVIDIA or if there's something else at a lower layer doing something like this. Unfortunately, I don't know enough about NVIDIA GPUs to have an more educated guess though, so perhaps someone else can provide an answer :-)

But as far as I can tell the runtime and compiler seem to be doing the correct thing with regards to not mapping the pointer data. And if it was a mapper being triggered, like this PR was trying to prevent, you'd see it in the MLIR and the runtime trace (there would likely be more maps in the trace that look different to the regular ones, and MLIR has a specific mapper field for maps and operation with a region for the mapper itself).

https://github.com/llvm/llvm-project/pull/177848