[clang] [C++20] [Modules] Introduce -fgen-reduced-bmi (PR #85050)
Chuanqi Xu via cfe-commits
cfe-commits at lists.llvm.org
Wed Mar 13 02:25:00 PDT 2024
https://github.com/ChuanqiXu9 created https://github.com/llvm/llvm-project/pull/85050
This is the driver part of https://github.com/llvm/llvm-project/pull/75894.
This patch introduces '-fgen-reduced-bmi' to enable generating the reduced BMI.
This patch did:
- When `-fgen-reduced-bmi` is specified but `--precompile` is not specified for a module unit, we'll skip the precompile phase to avoid unnecessary two-phase compilation phases. Then if `-c` is specified, we will generate the reduced BMI in CodeGenAction as a by-product.
- When `-fgen-reduced-bmi` is specified and `--precompile` is specified, we will generate the reduced BMI in GenerateModuleInterfaceAction as a by-product.
- When `-fgen-reduced-bmi` is specified for a non-module unit. We don't do anything nor try to give a warn. This is more user friendly so that the end users can try to test and experiment with the feature without asking help from the build systems.
The core design idea is that users should be able to enable this easily with the existing cmake mechanisms.
The future plan for the flag is:
- Add this to clang19 and make it opt-in for 1~2 releases. It depends on the testing feedback to decide how long we like to make it opt-in.
- Then we can announce the existing BMI generating may be deprecated and suggesting people (end users or build systems) to enable this for 1~2 releases.
- Finally we will enable this by default. When that time comes, the term `BMI` will refer to the reduced BMI today and the existing BMI will only be meaningful to build systems which loves to support two phase compilations.
I'll send release notes and document in seperate commits after this get landed.
>From 77c66427c279689256f007cc5706b5f74e47f9e6 Mon Sep 17 00:00:00 2001
From: Chuanqi Xu <yedeng.yd at linux.alibaba.com>
Date: Tue, 12 Mar 2024 17:26:49 +0800
Subject: [PATCH] [C++20] [Modules] Introduce -fgen-reduced-bmi
---
clang/include/clang/CodeGen/CodeGenAction.h | 2 +
clang/include/clang/Driver/Options.td | 6 +++
.../include/clang/Frontend/FrontendOptions.h | 9 +++-
clang/include/clang/Serialization/ASTWriter.h | 7 +--
clang/lib/CodeGen/CodeGenAction.cpp | 19 +++++++
clang/lib/Driver/Driver.cpp | 27 +++++-----
clang/lib/Driver/ToolChains/Clang.cpp | 41 ++++++++++++--
clang/lib/Driver/ToolChains/Clang.h | 14 +++++
clang/lib/Frontend/FrontendActions.cpp | 7 +++
clang/lib/Frontend/PrecompiledPreamble.cpp | 3 +-
clang/lib/Serialization/GeneratePCH.cpp | 23 ++++++--
.../test/Driver/module-fgen-reduced-bmi.cppm | 53 +++++++++++++++++++
clang/test/Modules/gen-reduced-bmi.cppm | 36 +++++++++++++
13 files changed, 220 insertions(+), 27 deletions(-)
create mode 100644 clang/test/Driver/module-fgen-reduced-bmi.cppm
create mode 100644 clang/test/Modules/gen-reduced-bmi.cppm
diff --git a/clang/include/clang/CodeGen/CodeGenAction.h b/clang/include/clang/CodeGen/CodeGenAction.h
index 7ad2988e589eb2..186dbb43f01ef7 100644
--- a/clang/include/clang/CodeGen/CodeGenAction.h
+++ b/clang/include/clang/CodeGen/CodeGenAction.h
@@ -57,6 +57,8 @@ class CodeGenAction : public ASTFrontendAction {
bool loadLinkModules(CompilerInstance &CI);
protected:
+ bool BeginSourceFileAction(CompilerInstance &CI) override;
+
/// Create a new code generation action. If the optional \p _VMContext
/// parameter is supplied, the action uses it without taking ownership,
/// otherwise it creates a fresh LLVM context and takes ownership.
diff --git a/clang/include/clang/Driver/Options.td b/clang/include/clang/Driver/Options.td
index aca8c9b0d5487a..b8ceeff9362df9 100644
--- a/clang/include/clang/Driver/Options.td
+++ b/clang/include/clang/Driver/Options.td
@@ -3018,6 +3018,7 @@ defm prebuilt_implicit_modules : BoolFOption<"prebuilt-implicit-modules",
def fmodule_output_EQ : Joined<["-"], "fmodule-output=">,
Flags<[NoXarchOption]>, Visibility<[ClangOption, CC1Option]>,
+ MarshallingInfoString<FrontendOpts<"ModuleOutputPath">>,
HelpText<"Save intermediate module file results when compiling a standard C++ module unit.">;
def fmodule_output : Flag<["-"], "fmodule-output">, Flags<[NoXarchOption]>,
Visibility<[ClangOption, CC1Option]>,
@@ -3031,6 +3032,11 @@ defm skip_odr_check_in_gmf : BoolOption<"f", "skip-odr-check-in-gmf",
"Perform ODR checks for decls in the global module fragment.">>,
Group<f_Group>;
+def gen_reduced_bmi : Flag<["-"], "fgen-reduced-bmi">,
+ Group<i_Group>, Visibility<[ClangOption, CC1Option]>,
+ HelpText<"Generate the reduced BMI">,
+ MarshallingInfoFlag<FrontendOpts<"GenReducedBMI">>;
+
def fmodules_prune_interval : Joined<["-"], "fmodules-prune-interval=">, Group<i_Group>,
Visibility<[ClangOption, CC1Option]>, MetaVarName<"<seconds>">,
HelpText<"Specify the interval (in seconds) between attempts to prune the module cache">,
diff --git a/clang/include/clang/Frontend/FrontendOptions.h b/clang/include/clang/Frontend/FrontendOptions.h
index 8085dbcbf671a6..ddfd4f30d1b773 100644
--- a/clang/include/clang/Frontend/FrontendOptions.h
+++ b/clang/include/clang/Frontend/FrontendOptions.h
@@ -387,6 +387,10 @@ class FrontendOptions {
LLVM_PREFERRED_TYPE(bool)
unsigned ModulesShareFileManager : 1;
+ /// Whether to generate reduced BMI for C++20 named modules.
+ LLVM_PREFERRED_TYPE(bool)
+ unsigned GenReducedBMI : 1;
+
CodeCompleteOptions CodeCompleteOpts;
/// Specifies the output format of the AST.
@@ -553,6 +557,9 @@ class FrontendOptions {
/// Path which stores the output files for -ftime-trace
std::string TimeTracePath;
+ /// Output Path for module output file.
+ std::string ModuleOutputPath;
+
public:
FrontendOptions()
: DisableFree(false), RelocatablePCH(false), ShowHelp(false),
@@ -565,7 +572,7 @@ class FrontendOptions {
BuildingImplicitModuleUsesLock(true), ModulesEmbedAllFiles(false),
IncludeTimestamps(true), UseTemporary(true),
AllowPCMWithCompilerErrors(false), ModulesShareFileManager(true),
- TimeTraceGranularity(500) {}
+ GenReducedBMI(false), TimeTraceGranularity(500) {}
/// getInputKindForExtension - Return the appropriate input kind for a file
/// extension. For example, "c" would return Language::C.
diff --git a/clang/include/clang/Serialization/ASTWriter.h b/clang/include/clang/Serialization/ASTWriter.h
index 3ed9803fa3745b..bd310b6c7a5cdd 100644
--- a/clang/include/clang/Serialization/ASTWriter.h
+++ b/clang/include/clang/Serialization/ASTWriter.h
@@ -846,7 +846,7 @@ class ASTWriter : public ASTDeserializationListener,
/// AST and semantic-analysis consumer that generates a
/// precompiled header from the parsed source code.
class PCHGenerator : public SemaConsumer {
- const Preprocessor &PP;
+ Preprocessor &PP;
std::string OutputFile;
std::string isysroot;
Sema *SemaPtr;
@@ -867,11 +867,12 @@ class PCHGenerator : public SemaConsumer {
DiagnosticsEngine &getDiagnostics() const {
return SemaPtr->getDiagnostics();
}
+ Preprocessor &getPreprocessor() { return PP; }
virtual Module *getEmittingModule(ASTContext &Ctx);
public:
- PCHGenerator(const Preprocessor &PP, InMemoryModuleCache &ModuleCache,
+ PCHGenerator(Preprocessor &PP, InMemoryModuleCache &ModuleCache,
StringRef OutputFile, StringRef isysroot,
std::shared_ptr<PCHBuffer> Buffer,
ArrayRef<std::shared_ptr<ModuleFileExtension>> Extensions,
@@ -893,7 +894,7 @@ class ReducedBMIGenerator : public PCHGenerator {
virtual Module *getEmittingModule(ASTContext &Ctx) override;
public:
- ReducedBMIGenerator(const Preprocessor &PP, InMemoryModuleCache &ModuleCache,
+ ReducedBMIGenerator(Preprocessor &PP, InMemoryModuleCache &ModuleCache,
StringRef OutputFile);
void HandleTranslationUnit(ASTContext &Ctx) override;
diff --git a/clang/lib/CodeGen/CodeGenAction.cpp b/clang/lib/CodeGen/CodeGenAction.cpp
index bb9aaba025fa59..3737c99847f04f 100644
--- a/clang/lib/CodeGen/CodeGenAction.cpp
+++ b/clang/lib/CodeGen/CodeGenAction.cpp
@@ -25,8 +25,11 @@
#include "clang/CodeGen/ModuleBuilder.h"
#include "clang/Driver/DriverDiagnostic.h"
#include "clang/Frontend/CompilerInstance.h"
+#include "clang/Frontend/FrontendActions.h"
#include "clang/Frontend/FrontendDiagnostic.h"
+#include "clang/Frontend/MultiplexConsumer.h"
#include "clang/Lex/Preprocessor.h"
+#include "clang/Serialization/ASTWriter.h"
#include "llvm/ADT/Hashing.h"
#include "llvm/Bitcode/BitcodeReader.h"
#include "llvm/CodeGen/MachineOptimizationRemarkEmitter.h"
@@ -1003,6 +1006,12 @@ CodeGenerator *CodeGenAction::getCodeGenerator() const {
return BEConsumer->getCodeGenerator();
}
+bool CodeGenAction::BeginSourceFileAction(CompilerInstance &CI) {
+ if (CI.getFrontendOpts().GenReducedBMI)
+ CI.getLangOpts().setCompilingModule(LangOptions::CMK_ModuleInterface);
+ return true;
+}
+
static std::unique_ptr<raw_pwrite_stream>
GetOutputStream(CompilerInstance &CI, StringRef InFile, BackendAction Action) {
switch (Action) {
@@ -1061,6 +1070,16 @@ CodeGenAction::CreateASTConsumer(CompilerInstance &CI, StringRef InFile) {
CI.getPreprocessor().addPPCallbacks(std::move(Callbacks));
}
+ if (CI.getFrontendOpts().GenReducedBMI &&
+ !CI.getFrontendOpts().ModuleOutputPath.empty()) {
+ std::vector<std::unique_ptr<ASTConsumer>> Consumers{2};
+ Consumers[0] = std::move(Result);
+ Consumers[1] = std::make_unique<ReducedBMIGenerator>(
+ CI.getPreprocessor(), CI.getModuleCache(),
+ CI.getFrontendOpts().ModuleOutputPath);
+ return std::make_unique<MultiplexConsumer>(std::move(Consumers));
+ }
+
return std::move(Result);
}
diff --git a/clang/lib/Driver/Driver.cpp b/clang/lib/Driver/Driver.cpp
index 190782a79a2456..872ea905f01a03 100644
--- a/clang/lib/Driver/Driver.cpp
+++ b/clang/lib/Driver/Driver.cpp
@@ -4737,6 +4737,14 @@ Action *Driver::ConstructPhaseAction(
if (Args.hasArg(options::OPT_extract_api))
return C.MakeAction<ExtractAPIJobAction>(Input, types::TY_API_INFO);
+ // With '-fgen-reduced-bmi', we don't want to run the precompile phase
+ // unless the user specified '--precompile'. In the case the '--precompile'
+ // flag is enabled, we will try to emit the reduced BMI as a by product
+ // in GenerateModuleInterfaceAction.
+ if (Args.hasArg(options::OPT_gen_reduced_bmi) &&
+ !Args.getLastArg(options::OPT__precompile))
+ return Input;
+
types::ID OutputTy = getPrecompiledType(Input->getType());
assert(OutputTy != types::TY_INVALID &&
"Cannot precompile this input type!");
@@ -5802,19 +5810,8 @@ static const char *GetModuleOutputPath(Compilation &C, const JobAction &JA,
(C.getArgs().hasArg(options::OPT_fmodule_output) ||
C.getArgs().hasArg(options::OPT_fmodule_output_EQ)));
- if (Arg *ModuleOutputEQ =
- C.getArgs().getLastArg(options::OPT_fmodule_output_EQ))
- return C.addResultFile(ModuleOutputEQ->getValue(), &JA);
-
- SmallString<64> OutputPath;
- Arg *FinalOutput = C.getArgs().getLastArg(options::OPT_o);
- if (FinalOutput && C.getArgs().hasArg(options::OPT_c))
- OutputPath = FinalOutput->getValue();
- else
- OutputPath = BaseInput;
-
- const char *Extension = types::getTypeTempSuffix(JA.getType());
- llvm::sys::path::replace_extension(OutputPath, Extension);
+ SmallString<256> OutputPath =
+ tools::getCXX20NamedModuleOutputPath(C.getArgs(), BaseInput);
return C.addResultFile(C.getArgs().MakeArgString(OutputPath.c_str()), &JA);
}
@@ -5901,8 +5898,10 @@ const char *Driver::GetNamedOutputPath(Compilation &C, const JobAction &JA,
// If we're emitting a module output with the specified option
// `-fmodule-output`.
if (!AtTopLevel && isa<PrecompileJobAction>(JA) &&
- JA.getType() == types::TY_ModuleFile && SpecifiedModuleOutput)
+ JA.getType() == types::TY_ModuleFile && SpecifiedModuleOutput) {
+ assert(!C.getArgs().hasArg(options::OPT_gen_reduced_bmi));
return GetModuleOutputPath(C, JA, BaseInput);
+ }
// Output to a temporary file?
if ((!AtTopLevel && !isSaveTempsEnabled() &&
diff --git a/clang/lib/Driver/ToolChains/Clang.cpp b/clang/lib/Driver/ToolChains/Clang.cpp
index 3a7a1cf99c79ac..7877c1d873bb04 100644
--- a/clang/lib/Driver/ToolChains/Clang.cpp
+++ b/clang/lib/Driver/ToolChains/Clang.cpp
@@ -3777,6 +3777,24 @@ bool Driver::getDefaultModuleCachePath(SmallVectorImpl<char> &Result) {
return false;
}
+llvm::SmallString<256>
+clang::driver::tools::getCXX20NamedModuleOutputPath(const ArgList &Args,
+ const char *BaseInput) {
+ if (Arg *ModuleOutputEQ = Args.getLastArg(options::OPT_fmodule_output_EQ))
+ return StringRef(ModuleOutputEQ->getValue());
+
+ SmallString<256> OutputPath;
+ if (Arg *FinalOutput = Args.getLastArg(options::OPT_o);
+ FinalOutput && Args.hasArg(options::OPT_c))
+ OutputPath = FinalOutput->getValue();
+ else
+ OutputPath = BaseInput;
+
+ const char *Extension = types::getTypeTempSuffix(types::TY_ModuleFile);
+ llvm::sys::path::replace_extension(OutputPath, Extension);
+ return OutputPath;
+}
+
static bool RenderModulesOptions(Compilation &C, const Driver &D,
const ArgList &Args, const InputInfo &Input,
const InputInfo &Output, bool HaveStd20,
@@ -3965,9 +3983,26 @@ static bool RenderModulesOptions(Compilation &C, const Driver &D,
// module fragment.
CmdArgs.push_back("-fskip-odr-check-in-gmf");
- // Claim `-fmodule-output` and `-fmodule-output=` to avoid unused warnings.
- Args.ClaimAllArgs(options::OPT_fmodule_output);
- Args.ClaimAllArgs(options::OPT_fmodule_output_EQ);
+ // Noop if we see '-fgen-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.
+ if (Args.hasArg(options::OPT_gen_reduced_bmi) &&
+ (Input.getType() == driver::types::TY_CXXModule ||
+ Input.getType() == driver::types::TY_PP_CXXModule)) {
+ CmdArgs.push_back("-fgen-reduced-bmi");
+
+ if (Args.hasArg(options::OPT_fmodule_output_EQ))
+ Args.AddLastArg(CmdArgs, options::OPT_fmodule_output_EQ);
+ else
+ CmdArgs.push_back(Args.MakeArgString(
+ "-fmodule-output=" +
+ getCXX20NamedModuleOutputPath(Args, Input.getBaseInput())));
+ } else {
+ // To avoid unused warnings.
+ Args.ClaimAllArgs(options::OPT_gen_reduced_bmi);
+ Args.ClaimAllArgs(options::OPT_fmodule_output);
+ Args.ClaimAllArgs(options::OPT_fmodule_output_EQ);
+ }
return HaveModules;
}
diff --git a/clang/lib/Driver/ToolChains/Clang.h b/clang/lib/Driver/ToolChains/Clang.h
index 0f503c4bd1c4fe..3b2639b4cc49f4 100644
--- a/clang/lib/Driver/ToolChains/Clang.h
+++ b/clang/lib/Driver/ToolChains/Clang.h
@@ -193,6 +193,20 @@ DwarfFissionKind getDebugFissionKind(const Driver &D,
const llvm::opt::ArgList &Args,
llvm::opt::Arg *&Arg);
+// Calculate the output path of the module file when compiling a module unit
+// with the `-fmodule-output` option or `-fmodule-output=` option specified.
+// The behavior is:
+// - If `-fmodule-output=` is specfied, then the module file is
+// writing to the value.
+// - Otherwise if the output object file of the module unit is specified, the
+// output path
+// of the module file should be the same with the output object file except
+// the corresponding suffix. This requires both `-o` and `-c` are specified.
+// - Otherwise, the output path of the module file will be the same with the
+// input with the corresponding suffix.
+llvm::SmallString<256>
+getCXX20NamedModuleOutputPath(const llvm::opt::ArgList &Args,
+ const char *BaseInput);
} // end namespace tools
} // end namespace driver
diff --git a/clang/lib/Frontend/FrontendActions.cpp b/clang/lib/Frontend/FrontendActions.cpp
index 81fcd8d5ae9bd3..7f1052c165d124 100644
--- a/clang/lib/Frontend/FrontendActions.cpp
+++ b/clang/lib/Frontend/FrontendActions.cpp
@@ -281,6 +281,13 @@ GenerateModuleInterfaceAction::CreateASTConsumer(CompilerInstance &CI,
if (Consumers.empty())
return nullptr;
+ if (CI.getFrontendOpts().GenReducedBMI &&
+ !CI.getFrontendOpts().ModuleOutputPath.empty()) {
+ Consumers.push_back(std::make_unique<ReducedBMIGenerator>(
+ CI.getPreprocessor(), CI.getModuleCache(),
+ CI.getFrontendOpts().ModuleOutputPath));
+ }
+
return std::make_unique<MultiplexConsumer>(std::move(Consumers));
}
diff --git a/clang/lib/Frontend/PrecompiledPreamble.cpp b/clang/lib/Frontend/PrecompiledPreamble.cpp
index 9b0ef30a14121b..fdf05c3613c956 100644
--- a/clang/lib/Frontend/PrecompiledPreamble.cpp
+++ b/clang/lib/Frontend/PrecompiledPreamble.cpp
@@ -290,8 +290,7 @@ class PrecompilePreambleAction : public ASTFrontendAction {
class PrecompilePreambleConsumer : public PCHGenerator {
public:
- PrecompilePreambleConsumer(PrecompilePreambleAction &Action,
- const Preprocessor &PP,
+ PrecompilePreambleConsumer(PrecompilePreambleAction &Action, Preprocessor &PP,
InMemoryModuleCache &ModuleCache,
StringRef isysroot,
std::shared_ptr<PCHBuffer> Buffer)
diff --git a/clang/lib/Serialization/GeneratePCH.cpp b/clang/lib/Serialization/GeneratePCH.cpp
index f54db36d4a0199..4260ba867ad28b 100644
--- a/clang/lib/Serialization/GeneratePCH.cpp
+++ b/clang/lib/Serialization/GeneratePCH.cpp
@@ -14,6 +14,7 @@
#include "clang/AST/ASTContext.h"
#include "clang/Frontend/FrontendDiagnostic.h"
#include "clang/Lex/HeaderSearch.h"
+#include "clang/Lex/HeaderSearchOptions.h"
#include "clang/Lex/Preprocessor.h"
#include "clang/Sema/SemaConsumer.h"
#include "clang/Serialization/ASTReader.h"
@@ -23,8 +24,8 @@
using namespace clang;
PCHGenerator::PCHGenerator(
- const Preprocessor &PP, InMemoryModuleCache &ModuleCache,
- StringRef OutputFile, StringRef isysroot, std::shared_ptr<PCHBuffer> Buffer,
+ Preprocessor &PP, InMemoryModuleCache &ModuleCache, StringRef OutputFile,
+ StringRef isysroot, std::shared_ptr<PCHBuffer> Buffer,
ArrayRef<std::shared_ptr<ModuleFileExtension>> Extensions,
bool AllowASTWithErrors, bool IncludeTimestamps,
bool BuildingImplicitModule, bool ShouldCacheASTInMemory,
@@ -88,7 +89,7 @@ ASTDeserializationListener *PCHGenerator::GetASTDeserializationListener() {
return &Writer;
}
-ReducedBMIGenerator::ReducedBMIGenerator(const Preprocessor &PP,
+ReducedBMIGenerator::ReducedBMIGenerator(Preprocessor &PP,
InMemoryModuleCache &ModuleCache,
StringRef OutputFile)
: PCHGenerator(
@@ -101,12 +102,26 @@ ReducedBMIGenerator::ReducedBMIGenerator(const Preprocessor &PP,
Module *ReducedBMIGenerator::getEmittingModule(ASTContext &Ctx) {
Module *M = Ctx.getCurrentNamedModule();
- assert(M->isNamedModuleUnit() &&
+ assert(M && M->isNamedModuleUnit() &&
"ReducedBMIGenerator should only be used with C++20 Named modules.");
return M;
}
void ReducedBMIGenerator::HandleTranslationUnit(ASTContext &Ctx) {
+ // FIMXE: We'd better to wrap such options to a new class ASTWriterOptions.
+ getPreprocessor()
+ .getHeaderSearchInfo()
+ .getHeaderSearchOpts()
+ .ModulesSkipDiagnosticOptions = true;
+ getPreprocessor()
+ .getHeaderSearchInfo()
+ .getHeaderSearchOpts()
+ .ModulesSkipHeaderSearchPaths = true;
+ getPreprocessor()
+ .getHeaderSearchInfo()
+ .getHeaderSearchOpts()
+ .ModulesSkipPragmaDiagnosticMappings = true;
+
PCHGenerator::HandleTranslationUnit(Ctx);
if (!isComplete())
diff --git a/clang/test/Driver/module-fgen-reduced-bmi.cppm b/clang/test/Driver/module-fgen-reduced-bmi.cppm
new file mode 100644
index 00000000000000..77afdf3e74e505
--- /dev/null
+++ b/clang/test/Driver/module-fgen-reduced-bmi.cppm
@@ -0,0 +1,53 @@
+// It is annoying to handle different slash direction
+// in Windows and Linux. So we disable the test on Windows
+// here.
+// REQUIRES: !system-windows
+// On AIX, the default output for `-c` may be `.s` instead of `.o`,
+// which makes the test fail. So disable the test on AIX.
+// REQUIRES: !system-aix
+//
+// RUN: rm -rf %t
+// RUN: mkdir %t
+// RUN: split-file %s %t
+//
+// RUN: %clang -std=c++20 %t/Hello.cppm -fmodule-output=%t/Hello.pcm \
+// RUN: -fgen-reduced-bmi -c -o %t/Hello.o -### 2>&1 | FileCheck %t/Hello.cppm
+//
+// RUN: %clang -std=c++20 %t/Hello.cppm \
+// RUN: -fgen-reduced-bmi -c -o %t/Hello.o -### 2>&1 | \
+// RUN: FileCheck %t/Hello.cppm --check-prefix=CHECK-UNSPECIFIED
+//
+// RUN: %clang -std=c++20 %t/Hello.cppm \
+// RUN: -fgen-reduced-bmi -c -### 2>&1 | \
+// RUN: FileCheck %t/Hello.cppm --check-prefix=CHECK-NO-O
+//
+// RUN: %clang -std=c++20 %t/Hello.cppm \
+// RUN: -fgen-reduced-bmi -c -o %t/AnotherName.o -### 2>&1 | \
+// RUN: FileCheck %t/Hello.cppm --check-prefix=CHECK-ANOTHER-NAME
+//
+// RUN: %clang -std=c++20 %t/Hello.cppm --precompile -fgen-reduced-bmi \
+// RUN: -o %t/Hello.full.pcm -### 2>&1 | FileCheck %t/Hello.cppm \
+// RUN: --check-prefix=CHECK-EMIT-MODULE-INTERFACE
+//
+// RUN: %clang -std=c++20 %t/Hello.cc -fgen-reduced-bmi -Wall -Werror \
+// RUN: -c -o %t/Hello.o -### 2>&1 | FileCheck %t/Hello.cc
+
+//--- Hello.cppm
+export module Hello;
+
+// Test that we won't generate the emit-module-interface as 2 phase compilation model.
+// CHECK-NOT: -emit-module-interface
+// CHECK: "-fgen-reduced-bmi"
+
+// CHECK-UNSPECIFIED: -fmodule-output={{.*}}/Hello.pcm
+
+// CHECK-NO-O: -fmodule-output={{.*}}/Hello.pcm
+// CHECK-ANOTHER-NAME: -fmodule-output={{.*}}/AnotherName.pcm
+
+// With `-emit-module-interface` specified, we should still see the `-emit-module-interface`
+// flag.
+// CHECK-EMIT-MODULE-INTERFACE: -emit-module-interface
+
+//--- Hello.cc
+
+// CHECK-NOT: "-fgen-reduced-bmi"
diff --git a/clang/test/Modules/gen-reduced-bmi.cppm b/clang/test/Modules/gen-reduced-bmi.cppm
new file mode 100644
index 00000000000000..8c08795ce4e453
--- /dev/null
+++ b/clang/test/Modules/gen-reduced-bmi.cppm
@@ -0,0 +1,36 @@
+// RUN: rm -rf %t
+// RUN: mkdir -p %t
+// RUN: split-file %s %t
+//
+// RUN: %clang_cc1 -std=c++20 %t/a.cppm -emit-reduced-module-interface -o %t/a.reduced.pcm
+// RUN: %clang_cc1 -std=c++20 %t/a.cppm -fgen-reduced-bmi -fmodule-output=%t/a.pcm \
+// RUN: -S -emit-llvm -o %t/a.ll
+//
+// Test that the generated BMI from `-fgen-reduced-bmi -fmodule-output=` is same with
+// `-emit-reduced-module-interface`.
+// RUN: diff %t/a.reduced.pcm %t/a.pcm
+//
+// Test that we can consume the produced BMI correctly.
+// RUN: %clang_cc1 -std=c++20 %t/b.cppm -fmodule-file=a=%t/a.pcm -fsyntax-only -verify
+//
+// RUN: rm -f %t/a.pcm
+// RUN: %clang_cc1 -std=c++20 %t/a.cppm -fgen-reduced-bmi -fmodule-output=%t/a.pcm \
+// RUN: -emit-module-interface -o %t/a.full.pcm
+// RUN: diff %t/a.reduced.pcm %t/a.pcm
+// RUN: not diff %t/a.pcm %t/a.full.pcm
+//
+// RUN: %clang_cc1 -std=c++20 %t/b.cppm -fmodule-file=a=%t/a.pcm -fsyntax-only -verify
+// RUN: %clang_cc1 -std=c++20 %t/b.cppm -fmodule-file=a=%t/a.full.pcm -fsyntax-only -verify
+
+//--- a.cppm
+export module a;
+export int a() {
+ return 43;
+}
+
+//--- b.cppm
+// Test that we can consume the produced BMI correctly as a smocking test.
+// expected-no-diagnostics
+export module b;
+import a;
+export int b() { return a(); }
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