[CIR] -emit-cir should not implicitly enable the CIR pipeline

clang/include/clang/Basic/DiagnosticDriverKinds.td

@@ -887,6 +887,9 @@ def warn_missing_include_dirs : Warning<
 def err_drv_malformed_warning_suppression_mapping : Error<
   "failed to process suppression mapping file '%0': %1">;
 
+def err_drv_emit_cir_without_fclangir : Error<
+  "-emit-cir is only valid with -fclangir">;
+
 def warn_drv_openacc_without_cir
     : Warning<"OpenACC directives will result in no runtime behavior; use "
               "-fclangir to enable runtime effect">,

clang/include/clang/Basic/DiagnosticFrontendKinds.td

@@ -136,6 +136,9 @@ def err_fe_action_not_available : Error<
     "action %0 not compiled in">;
 def err_fe_cir_not_built : Error<"clang IR support not available, rebuild "
                                  "clang with -DCLANG_ENABLE_CIR=ON">;
+def err_fe_cir_disabled : Error<
+  "trying to compile CIR module %0 with clang IR disabled; use "
+  "-fclangir to enable CIR pipeline">;
 def err_fe_invalid_multiple_actions : Error<
     "'%0' action ignored; '%1' action specified previously">;
 def err_fe_invalid_alignment : Error<

clang/lib/Frontend/CompilerInvocation.cpp

@@ -3139,9 +3139,17 @@ static bool ParseFrontendArgs(FrontendOptions &Opts, ArgList &Args,
   if (Opts.ProgramAction != frontend::GenerateModule && Opts.IsSystemModule)
     Diags.Report(diag::err_drv_argument_only_allowed_with) << "-fsystem-module"
                                                            << "-emit-module";
-  if (Args.hasArg(OPT_fclangir) || Args.hasArg(OPT_emit_cir))
+  if (Args.hasArg(OPT_fclangir))
     Opts.UseClangIRPipeline = true;
 
+#if CLANG_ENABLE_CIR
+  if (!Args.hasArg(OPT_fclangir) && Args.hasArg(OPT_emit_cir))
+    Diags.Report(diag::err_drv_emit_cir_without_fclangir);
+#else
+  if (Args.hasArg(OPT_emit_cir))
+    Diags.Report(diag::err_fe_cir_not_built);
+#endif
+
 #if CLANG_ENABLE_CIR
   if (Args.hasArg(OPT_clangir_disable_passes))
     Opts.ClangIRDisablePasses = true;

clang/lib/FrontendTool/ExecuteCompilerInvocation.cpp

@@ -49,12 +49,20 @@ CreateFrontendBaseAction(CompilerInstance &CI) {
   StringRef Action("unknown");
   (void)Action;
 
+#if CLANG_ENABLE_CIR
   unsigned UseCIR = CI.getFrontendOpts().UseClangIRPipeline;
-  frontend::ActionKind Act = CI.getFrontendOpts().ProgramAction;
-  bool EmitsCIR = Act == EmitCIR;
 
-  if (!UseCIR && EmitsCIR)
-    llvm::report_fatal_error("-emit-cir and only valid when using -fclangir");
+  if (!UseCIR) {
+    FrontendInputFile *it =
+        llvm::find_if(CI.getFrontendOpts().Inputs, [](const auto &FIF) {
+          return FIF.getKind().getLanguage() == Language::CIR;
+        });
+    if (it != CI.getFrontendOpts().Inputs.end()) {
+      CI.getDiagnostics().Report(diag::err_fe_cir_disabled) << it->getFile();
+      return nullptr;
+    }
+  }
+#endif
 
   switch (CI.getFrontendOpts().ProgramAction) {
   case ASTDeclList:            return std::make_unique<ASTDeclListAction>();

clang/test/CIR/CodeGen/builtin_prefetch.c

@@ -1,6 +1,6 @@
-// RUN: %clang_cc1 -triple x86_64-unknown-linux-gnu -emit-cir %s -o - | FileCheck %s -check-prefix=CIR
+// RUN: %clang_cc1 -triple x86_64-unknown-linux-gnu -fclangir -emit-cir %s -o - | FileCheck %s -check-prefix=CIR
 // RUN: %clang_cc1 -triple x86_64-unknown-linux-gnu -fclangir -emit-llvm %s -o - | FileCheck %s -check-prefix=LLVM
-// RUN: %clang_cc1 -triple x86_64-unknown-linux-gnu -emit-llvm %s -o - | FileCheck %s -check-prefix=OGCG
+// RUN: %clang_cc1 -triple x86_64-unknown-linux-gnu -fclangir -emit-llvm %s -o - | FileCheck %s -check-prefix=OGCG
 
 void foo(void *a) {
   __builtin_prefetch(a);        // rw=0, locality=3

clang/test/CIR/CodeGen/dlti.c

@@ -1,4 +1,4 @@
-// RUN: %clang_cc1 -triple x86_64-unknown-linux-gnu -emit-cir %s -o %t.cir
+// RUN: %clang_cc1 -triple x86_64-unknown-linux-gnu -fclangir -emit-cir %s -o %t.cir
 // RUN: FileCheck --input-file=%t.cir %s --check-prefix=LITTLE
 
 void foo() {}

clang/test/CIR/CodeGen/dlti_be.c

@@ -1,5 +1,5 @@
 // REQUIRES: aarch64-registered-target
-// RUN: %clang_cc1 -triple aarch64_be-linux-gnu -emit-cir %s -o %t.cir
+// RUN: %clang_cc1 -triple aarch64_be-linux-gnu -fclangir -emit-cir %s -o %t.cir
 // RUN: FileCheck --input-file=%t.cir %s --check-prefix=BIG
 
 void foo() {}

clang/test/CIR/CodeGen/module-asm.c

@@ -1,4 +1,4 @@
-// RUN: %clang_cc1 -triple x86_64-unknown-linux-gnu -emit-cir %s -o %t.cir 
+// RUN: %clang_cc1 -triple x86_64-unknown-linux-gnu -fclangir -emit-cir %s -o %t.cir 
 // RUN: FileCheck --input-file=%t.cir %s
 
 // CHECK:  cir.module_asm = [".globl bar", ".globl foo"]

clang/test/Driver/cir-flags-error.c

@@ -0,0 +1,11 @@
+// REQUIRES: cir-support
+
+// RUN: not %clang -emit-cir %s -o /dev/null 2>&1 | FileCheck %s -check-prefix=EMIT_CIR_ERROR
+// EMIT_CIR_ERROR: error: -emit-cir is only valid with -fclangir
+
+// RUN: %clang -fclangir -emit-cir %s -o /dev/null 2>&1 | FileCheck %s --allow-empty -check-prefix=EMIT_CIR_OK
+// EMIT_CIR_OK-NOT: error: -emit-cir is only valid with -fclangir
+
+int main(void) {
+  return 0;
+}

clang/test/Driver/cir-input-without-fclangir.cir

@@ -0,0 +1,20 @@
+// RUN: not %clang %s -emit-llvm -o /dev/null 2>&1 | FileCheck %s -check-prefix=CIR_INPUT_ERROR
+// CIR_INPUT_ERROR: error: trying to compile CIR module {{.*}} with clang IR disabled; use -fclangir to enable CIR pipeline
+
+// RUN: %clang -fclangir %s -emit-llvm -o /dev/null 2>&1 | FileCheck %s --allow-empty -check-prefix=CIR_INPUT_OK
+// CIR_INPUT_OK-NOT: error: trying to compile CIR module
+
+// REQUIRES: x86-registered-target
+// REQUIRES: cir-support
+
+!s32i = !cir.int<s, 32>
+
+module attributes {cir.lang = #cir.lang<cxx>, cir.triple = "x86_64-unknown-linux-gnu"} {
+  cir.func @test_function() -> !s32i {
+    %0 = cir.alloca !s32i, !cir.ptr<!s32i>, ["__retval"] {alignment = 4 : i64}
+    %1 = cir.const #cir.int<42> : !s32i
+    cir.store %1, %0 : !s32i, !cir.ptr<!s32i>
+    %2 = cir.load %0 : !cir.ptr<!s32i>, !s32i
+    cir.return %2 : !s32i
+  }
+}