[llvm] [NVPTX] Avoid introducing unnecessary ProxyRegs and Movs in ISel (PR #120486)

[Alex MacLean via llvm-commits]

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@@ -212,21 +208,6 @@ bool NVPTXDAGToDAGISel::tryIntrinsicChain(SDNode *N) {
   }
 }
 
-// There's no way to specify FP16 and BF16 immediates in .(b)f16 ops, so we
-// have to load them into an .(b)f16 register first.
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AlexMaclean wrote:

The comment is sort of true but it doesn't justify making things the way they were. It is simpler and cleaner to replace these with normally named Mov instructions and to use tablegen to generate the ISel logic. This is handled the same way any other instruction where we do not support an immediate operand is. 

https://github.com/llvm/llvm-project/pull/120486