[llvm] [LLVM][NVPTX]Add BF16 vector instruction and fix lowering rules (PR #69415)

[Han Shen via llvm-commits]

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@@ -629,7 +657,7 @@ let hasSideEffects = false in {
                 ToType, ".bf16 \t$dst, $src;"), []>,
       Requires<!if(!eq(ToType, "f32"),
                    // bf16->f32 was introduced early.
-                   [hasPTX<71>, hasSM<80>],
+                   [hasPTX<70>, hasSM<80>],
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shenh10 wrote:

You are correct. 
ptxas complains: Feature 'cvt with .f32.bf16' requires PTX ISA .version 7.1 or later

https://github.com/llvm/llvm-project/pull/69415