[llvm] [DebugInfo][RemoveDIs] Add local-utility plumbing for DPValues (PR #72276)

[Orlando Cazalet-Hyams via llvm-commits]

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@@ -2019,12 +2197,68 @@ void llvm::salvageDebugInfoForDbgValues(
     LLVM_DEBUG(dbgs() << "SALVAGE: " << *DII << '\n');
     Salvaged = true;
   }
+  // Duplicate of above block for DPValues.
+  for (auto *DPV : DPUsers) {
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OCHyams wrote:

If not for the isa<dbg.assign> check in the original I'd be tempted to say this function might be better templated rather than copy/pasted due to its size. Casts make it ugly to do so, alas. The size of the duplication makes me nervous, but I'm not sure what else we can do without introducing a load of utilities (something like `isaDbgValue(DbgVariableIntrinsic *)` +  `isaDbgValue(DPValue *)` etc).

https://github.com/llvm/llvm-project/pull/72276