[clang] [llvm] [AMDGPU] Add `nocreateundeforpoison` annotations (PR #166450)

[Matt Arsenault via llvm-commits]

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@@ -754,6 +754,19 @@ class MSBuiltin<string name> {
   string MSBuiltinName = name;
 }
 
+/// Utility class for intrinsics that
+/// 1. Don't touch memory or any hidden state
+/// 2. Can be freely speculated, and
+/// 3. Will not create undef or poison on defined inputs.
+class PureTotalIntrinsic<list<LLVMType> ret_types,
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arsenm wrote:

```suggestion
class PureIntrinsic<list<LLVMType> ret_types,
```

"Pure total" reads weird and the total seems redundant 

https://github.com/llvm/llvm-project/pull/166450