[llvm] [DebugInfo][SimpleLoopUnswitch] Fix missing debug location updates (PR #97662)

[Orlando Cazalet-Hyams via llvm-commits]

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@@ -1245,9 +1245,12 @@ static BasicBlock *buildClonedLoopBlocks(
       if (SE && isa<PHINode>(I))
         SE->forgetValue(&I);
 
+      Instruction *InsertPt = &*MergeBB->getFirstInsertionPt();
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OCHyams wrote:

Can we keep this as an iterator rather than dereference it? It has variable location implications in `Instruction::insertBefore` (more info [here](https://llvm.org/docs/RemoveDIsDebugInfo.html#api-changes) -TL;DR, there's an extra bit in iterators that determines whether the iterator points before this instruction only or additionally the debug records attached to it too).

https://github.com/llvm/llvm-project/pull/97662