[llvm] [NVPTX] Handle unreachable default in llvm::SwitchIns. (PR #72641)

[Artem Belevich via llvm-commits]

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@@ -138,7 +138,32 @@ bool NVPTXLowerUnreachable::runOnFunction(Function &F) {
   InlineAsm *Exit = InlineAsm::get(ExitFTy, "exit;", "", true);
 
   bool Changed = false;
+
+  // In scenarios where a Switch Instruction has an unreachable default
+  // successor, substituting the unreachable instruction with an exit
+  // instruction introduces an additional block in the Control Flow Graph
+  // (CFG), thereby negatively impacting performance. To mitigate this
+  // undesirable impact, we proactively refrain from processing blocks that
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Artem-B wrote:

I'm not completely convinced that 

https://github.com/llvm/llvm-project/pull/72641