[llvm] [DirectX] Make dx.RawBuffer an op that can't be replaced (PR #154620)

[Justin Bogner via llvm-commits]

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@@ -198,6 +203,111 @@ static void createLoadIntrinsic(IntrinsicInst *II, LoadInst *LI, Value *Offset,
   llvm_unreachable("Unhandled case in switch");
 }
 
+static void collectBlockUseDef(Instruction *Start,
+                               SmallVectorImpl<Instruction *> &Out) {
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bogner wrote:

Should this just return a `SmallVector<Instruction *>` rather than fill `Out`? I feel like that would be slightly clearer.

https://github.com/llvm/llvm-project/pull/154620