[clang] [CIR] Add framework for CIR to LLVM IR lowering (PR #124650)

[Andy Kaylor via cfe-commits]

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@@ -55,6 +56,13 @@ class EmitCIRAction : public CIRGenAction {
   EmitCIRAction(mlir::MLIRContext *MLIRCtx = nullptr);
 };
 
+class EmitLLVMAction : public CIRGenAction {
+  virtual void anchor();
+
+public:
+  EmitLLVMAction(mlir::MLIRContext *MLIRCtx = nullptr);
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andykaylor wrote:

This seems to be following a pattern established by CodeGenAction, and calling this without a context parameter is the normal case (in fact, it's the only case I see in the code). When the parameter is null, the CIRGenAction constructor allocates a new context. If a non-null pointer is passed, the constructor just uses it.

https://github.com/llvm/llvm-project/pull/124650