[flang][driver] add option to make all main program variable static (#121968)

Co-authored-by: Kiran Chandramohan <[email protected]>

Author: jeanPerier

clang/include/clang/Driver/Options.td

@@ -6945,6 +6945,9 @@ defm unsigned : OptInFC1FFlag<"unsigned", "Enables UNSIGNED type">;
 def fno_automatic : Flag<["-"], "fno-automatic">, Group<f_Group>,
   HelpText<"Implies the SAVE attribute for non-automatic local objects in subprograms unless RECURSIVE">;
 
+def fsave_main_program : Flag<["-"], "fsave-main-program">, Group<f_Group>,
+  HelpText<"Place all variables from the main program in static memory (otherwise scalars may be placed on the stack)">;
+
 defm stack_arrays : BoolOptionWithoutMarshalling<"f", "stack-arrays",
   PosFlag<SetTrue, [], [ClangOption], "Attempt to allocate array temporaries on the stack, no matter their size">,
   NegFlag<SetFalse, [], [ClangOption], "Allocate array temporaries on the heap (default)">>;

clang/lib/Driver/ToolChains/Flang.cpp

@@ -57,7 +57,8 @@ void Flang::addFortranDialectOptions(const ArgList &Args,
                             options::OPT_fno_automatic,
                             options::OPT_fhermetic_module_files,
                             options::OPT_frealloc_lhs,
-                            options::OPT_fno_realloc_lhs});
+                            options::OPT_fno_realloc_lhs,
+                            options::OPT_fsave_main_program});
 }
 
 void Flang::addPreprocessingOptions(const ArgList &Args,

flang/lib/Frontend/CompilerInvocation.cpp

@@ -766,6 +766,11 @@ static bool parseFrontendArgs(FrontendOptions &opts, llvm::opt::ArgList &args,
     opts.features.Enable(Fortran::common::LanguageFeature::DefaultSave);
   }
 
+  // -fsave-main-program
+  if (args.hasArg(clang::driver::options::OPT_fsave_main_program)) {
+    opts.features.Enable(Fortran::common::LanguageFeature::SaveMainProgram);
+  }
+
   if (args.hasArg(
           clang::driver::options::OPT_falternative_parameter_statement)) {
     opts.features.Enable(Fortran::common::LanguageFeature::OldStyleParameter);

flang/test/Driver/fsave-main-program.f90

@@ -0,0 +1,5 @@
+! Check that the driver passes through -fsave-main-program:
+! RUN: %flang -### -S -fsave-main-program %s -o - 2>&1 | FileCheck %s
+! Check that the compiler accepts -fsave-main-program:
+! RUN: %flang_fc1 -emit-hlfir -fsave-main-program %s -o -
+! CHECK: "-fc1"{{.*}}"-fsave-main-program"

flang/test/Lower/fsave-main-program.f90

@@ -0,0 +1,10 @@
+! Test -fsave-main-program switch.
+! RUN: %flang_fc1 -emit-hlfir -o - %s | FileCheck --check-prefix=CHECK-DEFAULT %s
+! RUN: %flang_fc1 -fsave-main-program -emit-hlfir -o - %s | FileCheck --check-prefix=CHECK-SAVE %s
+program test
+integer :: i
+call foo(i)
+end
+
+!CHECK-DEFAULT-NOT: fir.global internal @_QFEi
+!CHECK-SAVE: fir.global internal @_QFEi