[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)
+// Arch: 2*/3*/5*/6*/7*/8*/9*/10*/12*
+//
+// Family-specific: F*f : F*f > F* =>
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rajatbajpai wrote:

Is it easy to understand?

> The family-specific architectures have `f` feature suffix and they follow following order:
> + sm_X{Y2}f > sm_X{Y1}f iff Y2 > Y1
> + sm_XY{f} > sm_XY{}

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