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

[Farzon Lotfi via llvm-commits]

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@@ -3852,6 +3852,10 @@ bool llvm::canReplaceOperandWithVariable(const Instruction *I, unsigned OpIdx) {
   if (I->isLifetimeStartOrEnd())
     return false;
 
+  if (auto *TT = dyn_cast<TargetExtType>(Op->getType());
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farzonl wrote:

I could use some advice on where this should live?

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