[clang] [CIR] Build out AST consumer patterns to reach the entry point into CIRGen (PR #91007)

[Chuanqi Xu via cfe-commits]

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@@ -42,6 +47,14 @@ CreateFrontendBaseAction(CompilerInstance &CI) {
   StringRef Action("unknown");
   (void)Action;
 
+  auto UseCIR = CI.getFrontendOpts().UseClangIRPipeline;
+  auto Act = CI.getFrontendOpts().ProgramAction;
+  auto EmitsCIR = Act == EmitCIR;
+
+  if (!UseCIR && EmitsCIR)
+    llvm::report_fatal_error(
+        "-emit-cir and -emit-cir-only only valid when using -fclangir");
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ChuanqiXu9 wrote:

What is `-emit-cir-only`? Should we remove that?

https://github.com/llvm/llvm-project/pull/91007