[llvm] [SelectionDAG] Add an ISD::CLEAR_CACHE node to lower llvm.clear_cache (PR #93795)

[Matt Arsenault via llvm-commits]

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@@ -32387,6 +32390,10 @@ SDValue X86TargetLowering::LowerOperation(SDValue Op, SelectionDAG &DAG) const {
   case ISD::ADDRSPACECAST:      return LowerADDRSPACECAST(Op, DAG);
   case X86ISD::CVTPS2PH:        return LowerCVTPS2PH(Op, DAG);
   case ISD::PREFETCH:           return LowerPREFETCH(Op, Subtarget, DAG);
+  case ISD::CLEAR_CACHE: {
+    // X86 instruction cache is coherent with its data cache so this is a no-op.
+    return Op->getOperand(0);
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arsenm wrote:

Just delete the operation should probably be the default expansion. Probably should move this comment to the setOperationAction, and move this implementation to the default expand action 

https://github.com/llvm/llvm-project/pull/93795