[llvm] [NVPTX] Add family-specific architectures support (PR #141899)

[Rajat Bajpai via llvm-commits]

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@@ -33,20 +33,61 @@ class FeaturePTX<int version>:
    SubtargetFeature<"ptx"# version, "PTXVersion",
                     "" # version,
                     "Use PTX version " # version>;
-
+//
+// NVPTX Architecture Hierarchy and Ordering:
+// 
+// Family: 2/3/5/6/7/8/9/10/12 (Follows Onion model, older family is compatible with newer family)
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rajatbajpai wrote:

Does this make more sense?

> GPU architectures: sm_2Y/sm_3Y/sm_5Y/sm_6Y/sm_7Y/sm_8Y/sm_9Y/sm_10Y/sm_12Y (`Y` represents version within the architecture)
> The architectures have name of form `sm_XYz` where `X` represent the generation number, `Y` represents the version within the architecture, and `z` represents the optional feature suffix.
> For example, in `sm_103f` architecture, `10` represents `X`, `3` represents `Y`, and `f` represents `z`.


https://github.com/llvm/llvm-project/pull/141899