Don't warn

Author: ChuanqiXu9

clang/include/clang/Basic/DiagnosticDriverKinds.td

@@ -555,13 +555,6 @@ def err_test_module_file_extension_format : Error<
 def err_drv_module_output_with_multiple_arch : Error<
   "option '-fmodule-output' cannot be used with multiple arch options">;
 
-def warn_drv_module_reduced_bmi_not_enabled : Warning<
-  "reduced BMI is expected to be enabled by default in Clang 21; it can be enabled "
-  "explicitly by passing '-fmodules-reduced-bmi' (in one-phase compilation models, "
-  "like CMake) or by disabling the diagnostic and requesting the build system vendor "
-  "support reduced BMIs (in two-phase compilation models)">,
-  InGroup<DiagGroup<"missing-reduced-bmi">>;
-
 def warn_drv_delayed_template_parsing_after_cxx20 : Warning<
   "-fdelayed-template-parsing is deprecated after C++20">,
   InGroup<DiagGroup<"delayed-template-parsing-in-cxx20">>;

clang/lib/Driver/ToolChains/Clang.cpp

@@ -4267,14 +4267,6 @@ static bool RenderModulesOptions(Compilation &C, const Driver &D,
           getCXX20NamedModuleOutputPath(Args, Input.getBaseInput())));
   }
 
-  if ((Input.getType() == driver::types::TY_CXXModule ||
-       Input.getType() == driver::types::TY_PP_CXXModule) &&
-      (Args.hasArg(options::OPT_fmodule_output) ||
-       Args.hasArg(options::OPT_fmodule_output_EQ) ||
-       Args.hasArg(options::OPT__precompile)) &&
-      !Args.hasArg(options::OPT_modules_reduced_bmi))
-    D.Diag(diag::warn_drv_module_reduced_bmi_not_enabled);
-
   // Noop if we see '-fmodules-reduced-bmi' with other translation
   // units than module units. This is more user friendly to allow end uers to
   // enable this feature without asking for help from build systems.

clang/test/Driver/module-fgen-reduced-bmi.cppm

@@ -53,12 +53,6 @@
 // RUN:     -c -o Hello.o -### 2>&1 | FileCheck Hello.cc
 //
 // RUN: %clang -std=c++20 Hello.cppm -fmodule-output=Hello.pcm -c -o Hello.o \
-// RUN:     -### 2>&1 | FileCheck Hello.cppm -check-prefix=WARN
-//
-// RUN: %clang -std=c++20 Hello.cppm --precompile -o Hello.pcm \
-// RUN:     -### 2>&1 | FileCheck Hello.cppm -check-prefix=WARN
-//
-// RUN: %clang -std=c++20 Hello.cppm -fmodule-output=Hello.pcm -c -o Hello.o \
 // RUN:     -Wno-missing-reduced-bmi -### 2>&1 | FileCheck Hello.cppm -check-prefix=NO_WARN
 //
 // RUN: %clang -std=c++20 Hello.cppm --precompile -o Hello.pcm \
@@ -80,7 +74,6 @@ export module Hello;
 // flag.
 // CHECK-EMIT-MODULE-INTERFACE: -emit-module-interface
 
-// WARN: reduced BMI is expected to be enabled by default in Clang 21;
 // NO_WARN-NOT: warning
 
 //--- Hello.cc