[llvm] [NVPTX] Implement shouldBuildLookupTablesForConstant (PR #220088)

[Antonio Frighetto via llvm-commits]

================
@@ -636,6 +637,31 @@ void NVPTXTTIImpl::collectKernelLaunchBounds(
     LB.push_back({"maxntidz", MaxNTID[2]});
 }
 
+// A switch lookup table is materialized as an array with an initializer. PTX
+// only allows a variable's initial value to name a symbol in the .global or
+// .const state space; ptxas rejects anything else with "Variable used as
+// initial value not in .global or .const state space".
+bool NVPTXTTIImpl::shouldBuildLookupTablesForConstant(Constant *C) const {
+  SmallVector<Constant *, 8> WorkList = {C};
+  SmallPtrSet<Constant *, 8> Visited = {C};
----------------
antoniofrighetto wrote:

We could also update the doc-comment above to make this explicit. I understand the concern, but I think, in general, we should avoid introducing complexity unless needed, and I believe it shouldn't be the case here.

https://github.com/llvm/llvm-project/pull/220088