[llvm] [NVPTX] Cleanup NVPTXLowerArgs, simplifying logic and improving alignment propagation (PR #180286)

[Alex MacLean via llvm-commits]

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@@ -285,28 +285,6 @@ static void convertToParamAS(Use *OldUse, Value *Param, bool HasCvtaParam,
         if (SI->getFalseValue() == I.OldUse->get())
           SI->setFalseValue(ParamInGenericAS);
       }
-
-      // Escapes or writes can only use generic param pointers if
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AlexMaclean wrote:

This function can now actually be simplified further. It now simple propagates param address space to intermediate instructions such as GEPs and bitcasts and final users (loads and memcpy). While this is complete subset of what IAS does, I think we need to do it here for correctness on older HW where cvta.param is not supported. It feels wrong to insert unsupported instructions and rely on a separate optimization pass to remove them. 

https://github.com/llvm/llvm-project/pull/180286