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

The current way of lowering `llvm.clear_cache` is a bit unusual. As
suggested by Matt Arsenault we are better off using an ISD node.

This change introduces a new `ISD::CLEAR_CACHE`, registers a new libcall
by default named `__clear_cache` and the default legalisation is a
libcall.

This is preparatory work for a custom lowering of `ISD::CLEAR_CACHE`
needed by RISC-V on some platforms.

1 files changed, 4 insertions, 0 deletions

diff --git a/llvm/lib/CodeGen/TargetLoweringBase.cpp b/llvm/lib/CodeGen/TargetLoweringBase.cpp
index f2e4632..3aec704 100644
--- a/llvm/lib/CodeGen/TargetLoweringBase.cpp
+++ b/llvm/lib/CodeGen/TargetLoweringBase.cpp
@@ -1035,6 +1035,10 @@ void TargetLoweringBase::initActions() {
     setOperationAction(ISD::SET_FPMODE, VT, Expand);
   }
   setOperationAction(ISD::RESET_FPMODE, MVT::Other, Expand);
+
+  // This one by default will call __clear_cache unless the target
+  // wants something different.
+  setOperationAction(ISD::CLEAR_CACHE, MVT::Other, LibCall);
 }
 
 MVT TargetLoweringBase::getScalarShiftAmountTy(const DataLayout &DL,