Author: Kaviya Rajendiran
Date: 2026-08-20T12:18:22+05:30
New Revision: bc0c028fa5a3e8a76bc432f5b22d1ee4883acaca

URL: 
https://github.com/llvm/llvm-project/commit/bc0c028fa5a3e8a76bc432f5b22d1ee4883acaca
DIFF: 
https://github.com/llvm/llvm-project/commit/bc0c028fa5a3e8a76bc432f5b22d1ee4883acaca.diff

LOG: [Flang][Driver] Add support for option -f[no-]split-machine-functions in 
flang (#216637)

Added support for the `-fsplit-machine-functions` flag in the
Flang driver.

- The Flang driver forwards `-fsplit-machine-functions` to `-fc1` and
the negative flag `-fno-split-machine-functions` is used at the driver
level only.
- Flang `-fc1` driver sets `TargetOptions.EnableMachineFunctionSplitter`,
which causes LLVM's MachineFunctionSplitterPass to be added to the
codegen pipeline

Added: 
    flang/test/Driver/fsplit-machine-functions.f90
    flang/test/Driver/split-machine-function-pass.f90

Modified: 
    clang/include/clang/Driver/CommonArgs.h
    clang/include/clang/Options/Options.td
    clang/lib/Driver/ToolChains/Clang.cpp
    clang/lib/Driver/ToolChains/CommonArgs.cpp
    clang/lib/Driver/ToolChains/Flang.cpp
    flang/include/flang/Frontend/TargetOptions.h
    flang/lib/Frontend/CompilerInstance.cpp
    flang/lib/Frontend/CompilerInvocation.cpp

Removed: 
    


################################################################################
diff  --git a/clang/include/clang/Driver/CommonArgs.h 
b/clang/include/clang/Driver/CommonArgs.h
index 3b53df94fc79f..be15d15a1661e 100644
--- a/clang/include/clang/Driver/CommonArgs.h
+++ b/clang/include/clang/Driver/CommonArgs.h
@@ -257,6 +257,11 @@ void addMachineOutlinerArgs(const Driver &D, const 
llvm::opt::ArgList &Args,
                             const llvm::Triple &Triple, bool IsLTO,
                             const StringRef PluginOptPrefix = "");
 
+void addSplitMachineFunctionsArgs(const Driver &D,
+                                  const llvm::opt::ArgList &Args,
+                                  llvm::opt::ArgStringList &CmdArgs,
+                                  const llvm::Triple &Triple);
+
 void addOpenMPDeviceRTL(const Driver &D, const llvm::opt::ArgList &DriverArgs,
                         llvm::opt::ArgStringList &CC1Args,
                         StringRef BitcodeSuffix, const llvm::Triple &Triple,

diff  --git a/clang/include/clang/Options/Options.td 
b/clang/include/clang/Options/Options.td
index adc4224dd561c..7eacbc7a44827 100644
--- a/clang/include/clang/Options/Options.td
+++ b/clang/include/clang/Options/Options.td
@@ -5068,8 +5068,8 @@ defm separate_named_sections : 
BoolFOption<"separate-named-sections",
 
 defm split_machine_functions: BoolFOption<"split-machine-functions",
   CodeGenOpts<"SplitMachineFunctions">, DefaultFalse,
-  PosFlag<SetTrue, [], [ClangOption, CC1Option], "Enable">,
-  NegFlag<SetFalse, [], [ClangOption], "Disable">,
+  PosFlag<SetTrue, [], [ClangOption, CC1Option, FlangOption, FC1Option], 
"Enable">,
+  NegFlag<SetFalse, [], [ClangOption, FlangOption], "Disable">,
   BothFlags<[], [ClangOption], " late function splitting using profile 
information (x86 and aarch64 ELF)">>;
 
 defm partition_static_data_sections: 
BoolFOption<"partition-static-data-sections",

diff  --git a/clang/lib/Driver/ToolChains/Clang.cpp 
b/clang/lib/Driver/ToolChains/Clang.cpp
index 54583fe3abbd8..ccc226eff0782 100644
--- a/clang/lib/Driver/ToolChains/Clang.cpp
+++ b/clang/lib/Driver/ToolChains/Clang.cpp
@@ -6618,17 +6618,7 @@ void Clang::ConstructJob(Compilation &C, const JobAction 
&JA,
   Args.addOptInFlag(CmdArgs, options::OPT_funique_basic_block_section_names,
                     options::OPT_fno_unique_basic_block_section_names);
 
-  if (Arg *A = Args.getLastArg(options::OPT_fsplit_machine_functions,
-                               options::OPT_fno_split_machine_functions)) {
-    if (!A->getOption().matches(options::OPT_fno_split_machine_functions)) {
-      // This codegen pass is only available on x86 and AArch64 ELF targets.
-      if ((Triple.isX86() || Triple.isAArch64()) && Triple.isOSBinFormatELF())
-        A->render(Args, CmdArgs);
-      else
-        D.Diag(diag::err_drv_unsupported_opt_for_target)
-            << A->getAsString(Args) << TripleStr;
-    }
-  }
+  addSplitMachineFunctionsArgs(D, Args, CmdArgs, Triple);
 
   if (Arg *A =
           Args.getLastArg(options::OPT_fpartition_static_data_sections,

diff  --git a/clang/lib/Driver/ToolChains/CommonArgs.cpp 
b/clang/lib/Driver/ToolChains/CommonArgs.cpp
index e1c07fb94ea76..7db070699b23f 100644
--- a/clang/lib/Driver/ToolChains/CommonArgs.cpp
+++ b/clang/lib/Driver/ToolChains/CommonArgs.cpp
@@ -3086,6 +3086,23 @@ void tools::addMachineOutlinerArgs(const Driver &D,
     addArg(Twine("-codegen-data-use-path=") + CodeGenDataUseArg->getValue());
 }
 
+void tools::addSplitMachineFunctionsArgs(const Driver &D,
+                                         const llvm::opt::ArgList &Args,
+                                         llvm::opt::ArgStringList &CmdArgs,
+                                         const llvm::Triple &Triple) {
+  if (Arg *A = Args.getLastArg(options::OPT_fsplit_machine_functions,
+                               options::OPT_fno_split_machine_functions)) {
+    if (!A->getOption().matches(options::OPT_fno_split_machine_functions)) {
+      // This codegen pass is only available on x86 and AArch64 ELF targets.
+      if ((Triple.isX86() || Triple.isAArch64()) && Triple.isOSBinFormatELF())
+        A->render(Args, CmdArgs);
+      else
+        D.Diag(diag::err_drv_unsupported_opt_for_target)
+            << A->getAsString(Args) << Triple.getTriple();
+    }
+  }
+}
+
 void tools::addOpenMPDeviceRTL(const Driver &D,
                                const llvm::opt::ArgList &DriverArgs,
                                llvm::opt::ArgStringList &CC1Args,

diff  --git a/clang/lib/Driver/ToolChains/Flang.cpp 
b/clang/lib/Driver/ToolChains/Flang.cpp
index a40540691a254..5824f59400323 100644
--- a/clang/lib/Driver/ToolChains/Flang.cpp
+++ b/clang/lib/Driver/ToolChains/Flang.cpp
@@ -1233,6 +1233,8 @@ static void addPGOAndCoverageFlags(const ToolChain &TC, 
const JobAction &JA,
   if (Args.hasFlag(options::OPT_fpseudo_probe_for_profiling,
                    options::OPT_fno_pseudo_probe_for_profiling, false))
     CmdArgs.push_back("-fpseudo-probe-for-profiling");
+
+  addSplitMachineFunctionsArgs(TC.getDriver(), Args, CmdArgs, TC.getTriple());
 }
 
 void Flang::ConstructJob(Compilation &C, const JobAction &JA,

diff  --git a/flang/include/flang/Frontend/TargetOptions.h 
b/flang/include/flang/Frontend/TargetOptions.h
index f6e5634d5a995..fc7a2a3089f15 100644
--- a/flang/include/flang/Frontend/TargetOptions.h
+++ b/flang/include/flang/Frontend/TargetOptions.h
@@ -54,6 +54,9 @@ class TargetOptions {
   /// Print verbose assembly
   bool asmVerbose = false;
 
+  /// Enable splitting of machine functions using profile information.
+  bool SplitMachineFunctions = false;
+
   /// Atomic control options
   bool atomicIgnoreDenormalMode = false;
   bool atomicRemoteMemory = false;

diff  --git a/flang/lib/Frontend/CompilerInstance.cpp 
b/flang/lib/Frontend/CompilerInstance.cpp
index 02f39376f1d78..2416d3b593481 100644
--- a/flang/lib/Frontend/CompilerInstance.cpp
+++ b/flang/lib/Frontend/CompilerInstance.cpp
@@ -381,6 +381,7 @@ bool CompilerInstance::setUpTargetMachine() {
 
   llvm::TargetOptions tOpts = llvm::TargetOptions();
   tOpts.EnableAIXExtendedAltivecABI = targetOpts.EnableAIXExtendedAltivecABI;
+  tOpts.EnableMachineFunctionSplitter = targetOpts.SplitMachineFunctions;
   tOpts.VecLib = convertDriverVectorLibraryToVectorLibrary(CGOpts.getVecLib());
   tOpts.DisableIntegratedAS = CGOpts.DisableIntegratedAS;
   tOpts.FunctionSections = CGOpts.FunctionSections;

diff  --git a/flang/lib/Frontend/CompilerInvocation.cpp 
b/flang/lib/Frontend/CompilerInvocation.cpp
index b57bc4583be38..fef48a279ad72 100644
--- a/flang/lib/Frontend/CompilerInvocation.cpp
+++ b/flang/lib/Frontend/CompilerInvocation.cpp
@@ -610,6 +610,9 @@ static void parseTargetArgs(TargetOptions &opts, 
llvm::opt::ArgList &args) {
     }
   }
 
+  opts.SplitMachineFunctions =
+      args.hasArg(clang::options::OPT_fsplit_machine_functions);
+
   opts.asmVerbose = args.hasFlag(clang::options::OPT_fverbose_asm,
                                  clang::options::OPT_fno_verbose_asm, false);
 }

diff  --git a/flang/test/Driver/fsplit-machine-functions.f90 
b/flang/test/Driver/fsplit-machine-functions.f90
new file mode 100644
index 0000000000000..2a0ffe61811fc
--- /dev/null
+++ b/flang/test/Driver/fsplit-machine-functions.f90
@@ -0,0 +1,14 @@
+! Test handling of -fsplit-machine-functions and -fno-split-machine-functions.
+
+! RUN: %if x86-registered-target %{ %flang -### 
--target=x86_64-unknown-linux-gnu %s 2>&1 | FileCheck %s 
--check-prefix=NO-SPLIT-MACHINE-FUNCTIONS  %}
+! RUN: %if x86-registered-target %{ %flang -### 
--target=x86_64-unknown-linux-gnu -fsplit-machine-functions %s 2>&1 | FileCheck 
%s --check-prefix=SPLIT-MACHINE-FUNCTIONS  %}
+! RUN: %if x86-registered-target %{ %flang -### 
--target=x86_64-unknown-linux-gnu -fno-split-machine-functions %s 2>&1 | 
FileCheck %s --check-prefix=NO-SPLIT-MACHINE-FUNCTIONS  %}
+! RUN: %if x86-registered-target %{ %flang -### 
--target=x86_64-unknown-linux-gnu -fsplit-machine-functions 
-fno-split-machine-functions %s 2>&1 | FileCheck %s 
--check-prefix=NO-SPLIT-MACHINE-FUNCTIONS  %}
+! RUN: %if x86-registered-target %{ %flang -### 
--target=x86_64-unknown-linux-gnu -fno-split-machine-functions 
-fsplit-machine-functions %s 2>&1 | FileCheck %s 
--check-prefix=SPLIT-MACHINE-FUNCTIONS  %}
+! RUN: %if arm-registered-target %{ not %flang -### --target=arm-unknown-linux 
-fsplit-machine-functions %s 2>&1 | FileCheck %s --check-prefix=UNSUPPORTED-OPT 
%}
+! RUN: %if arm-registered-target %{ %flang -### --target=arm-unknown-linux 
-fno-split-machine-functions %s 2>&1 | FileCheck %s 
--check-prefix=NO-SPLIT-MACHINE-FUNCTIONS %}
+
+! SPLIT-MACHINE-FUNCTIONS: "-fsplit-machine-functions"
+! NO-SPLIT-MACHINE-FUNCTIONS-NOT: "-fsplit-machine-functions"
+! UNSUPPORTED-OPT: error: unsupported option '-fsplit-machine-functions' for 
target
+

diff  --git a/flang/test/Driver/split-machine-function-pass.f90 
b/flang/test/Driver/split-machine-function-pass.f90
new file mode 100644
index 0000000000000..cf8bd0eafb624
--- /dev/null
+++ b/flang/test/Driver/split-machine-function-pass.f90
@@ -0,0 +1,12 @@
+! Verify that the MachineFunctionSplitter pass is enabled while passing 
-fsplit-machine-functions.
+
+! REQUIRES: x86-registered-target
+
+! RUN: %flang_fc1 -S -fsplit-machine-functions %s -triple 
x86_64-unknown-linux-gnu -mllvm -debug-pass=Structure -o /dev/null 2>&1 | 
FileCheck %s --check-prefix=SPLIT
+! RUN: %flang_fc1 -S %s -triple x86_64-unknown-linux-gnu -mllvm 
-debug-pass=Structure -o /dev/null 2>&1 | FileCheck %s --check-prefix=NO-SPLIT
+
+! SPLIT: Machine Function Splitter Transformation
+! NO-SPLIT-NOT: Machine Function Splitter Transformation
+
+subroutine test
+end subroutine test


        
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