[flang] Add -fhermetic-module-files (#98083)

Module files emitted by this Fortran compiler are valid Fortran source files. Symbols that are USE-associated into modules are represented in their module files with USE statements and special comments with hash codes in them to ensure that those USE statements resolve to the same modules that were used to build the module when its module file was generated. This scheme prevents unchecked module file growth in large applications by not emitting USE-associated symbols redundantly. This problem can be especially bad when derived type definitions must be repeated in the module files of their clients, and the clients of those modules, and so on. However, this scheme has the disadvantage that clients of modules must be compiled with dependent modules in the module search path. This new -fhermetic-module-files option causes module file output to be free of dependences on any non-intrinsic module files; dependent modules are instead emitted as part of the module file, rather than being USE-associated. It is intended for top level library module files that are shipped with binary libraries when it is not convenient to collect and ship their dependent module files as well. Fixes #97398.
llvm · Jul 11, 2024 · 6598795 · 6598795
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diff --git a/clang/include/clang/Driver/Options.td b/clang/include/clang/Driver/Options.td
@@ -6687,6 +6687,9 @@ defm stack_arrays : BoolOptionWithoutMarshalling<"f", "stack-arrays",
 defm loop_versioning : BoolOptionWithoutMarshalling<"f", "version-loops-for-stride",
   PosFlag<SetTrue, [], [ClangOption], "Create unit-strided versions of loops">,
    NegFlag<SetFalse, [], [ClangOption], "Do not create unit-strided loops (default)">>;
+
+def fhermetic_module_files : Flag<["-"], "fhermetic-module-files">, Group<f_Group>,
+  HelpText<"Emit hermetic module files (no nested USE association)">;
 } // let Visibility = [FC1Option, FlangOption]
 
 def J : JoinedOrSeparate<["-"], "J">,

diff --git a/clang/lib/Driver/ToolChains/Flang.cpp b/clang/lib/Driver/ToolChains/Flang.cpp
@@ -35,18 +35,26 @@ static void addDashXForInput(const ArgList &Args, const InputInfo &Input,
 
 void Flang::addFortranDialectOptions(const ArgList &Args,
                                      ArgStringList &CmdArgs) const {
-  Args.addAllArgs(
-      CmdArgs, {options::OPT_ffixed_form, options::OPT_ffree_form,
-                options::OPT_ffixed_line_length_EQ, options::OPT_fopenacc,
-                options::OPT_finput_charset_EQ, options::OPT_fimplicit_none,
-                options::OPT_fno_implicit_none, options::OPT_fbackslash,
-                options::OPT_fno_backslash, options::OPT_flogical_abbreviations,
-                options::OPT_fno_logical_abbreviations,
-                options::OPT_fxor_operator, options::OPT_fno_xor_operator,
-                options::OPT_falternative_parameter_statement,
-                options::OPT_fdefault_real_8, options::OPT_fdefault_integer_8,
-                options::OPT_fdefault_double_8, options::OPT_flarge_sizes,
-                options::OPT_fno_automatic});
+  Args.addAllArgs(CmdArgs, {options::OPT_ffixed_form,
+                            options::OPT_ffree_form,
+                            options::OPT_ffixed_line_length_EQ,
+                            options::OPT_fopenacc,
+                            options::OPT_finput_charset_EQ,
+                            options::OPT_fimplicit_none,
+                            options::OPT_fno_implicit_none,
+                            options::OPT_fbackslash,
+                            options::OPT_fno_backslash,
+                            options::OPT_flogical_abbreviations,
+                            options::OPT_fno_logical_abbreviations,
+                            options::OPT_fxor_operator,
+                            options::OPT_fno_xor_operator,
+                            options::OPT_falternative_parameter_statement,
+                            options::OPT_fdefault_real_8,
+                            options::OPT_fdefault_integer_8,
+                            options::OPT_fdefault_double_8,
+                            options::OPT_flarge_sizes,
+                            options::OPT_fno_automatic,
+                            options::OPT_fhermetic_module_files});
 }
 
 void Flang::addPreprocessingOptions(const ArgList &Args,

diff --git a/flang/include/flang/Frontend/CompilerInvocation.h b/flang/include/flang/Frontend/CompilerInvocation.h
@@ -99,6 +99,7 @@ class CompilerInvocation : public CompilerInvocationBase {
   std::string moduleFileSuffix = ".mod";
 
   bool debugModuleDir = false;
+  bool hermeticModuleFileOutput = false;
 
   bool warnAsErr = false;
 
@@ -179,6 +180,11 @@ class CompilerInvocation : public CompilerInvocationBase {
   bool &getDebugModuleDir() { return debugModuleDir; }
   const bool &getDebugModuleDir() const { return debugModuleDir; }
 
+  bool &getHermeticModuleFileOutput() { return hermeticModuleFileOutput; }
+  const bool &getHermeticModuleFileOutput() const {
+    return hermeticModuleFileOutput;
+  }
+
   bool &getWarnAsErr() { return warnAsErr; }
   const bool &getWarnAsErr() const { return warnAsErr; }
 
@@ -244,6 +250,9 @@ class CompilerInvocation : public CompilerInvocationBase {
   }
 
   void setDebugModuleDir(bool flag) { debugModuleDir = flag; }
+  void setHermeticModuleFileOutput(bool flag) {
+    hermeticModuleFileOutput = flag;
+  }
 
   void setWarnAsErr(bool flag) { warnAsErr = flag; }
 

diff --git a/flang/include/flang/Semantics/semantics.h b/flang/include/flang/Semantics/semantics.h
@@ -307,10 +307,11 @@ class SemanticsContext {
 
 class Semantics {
 public:
-  explicit Semantics(SemanticsContext &context, parser::Program &program,
-      bool debugModuleWriter = false)
-      : context_{context}, program_{program} {
-    context.set_debugModuleWriter(debugModuleWriter);
+  explicit Semantics(SemanticsContext &context, parser::Program &program)
+      : context_{context}, program_{program} {}
+  Semantics &set_hermeticModuleFileOutput(bool yes = true) {
+    hermeticModuleFileOutput_ = yes;
+    return *this;
   }
 
   SemanticsContext &context() const { return context_; }
@@ -326,6 +327,7 @@ class Semantics {
 private:
   SemanticsContext &context_;
   parser::Program &program_;
+  bool hermeticModuleFileOutput_{false};
 };
 
 // Base class for semantics checkers.

diff --git a/flang/lib/Frontend/CompilerInvocation.cpp b/flang/lib/Frontend/CompilerInvocation.cpp
@@ -833,6 +833,11 @@ static bool parseSemaArgs(CompilerInvocation &res, llvm::opt::ArgList &args,
     res.setDebugModuleDir(true);
   }
 
+  // -fhermetic-module-files option
+  if (args.hasArg(clang::driver::options::OPT_fhermetic_module_files)) {
+    res.setHermeticModuleFileOutput(true);
+  }
+
   // -module-suffix
   if (const auto *moduleSuffix =
           args.getLastArg(clang::driver::options::OPT_module_suffix)) {

diff --git a/flang/lib/Frontend/FrontendAction.cpp b/flang/lib/Frontend/FrontendAction.cpp
@@ -180,11 +180,14 @@ bool FrontendAction::runSemanticChecks() {
   // so that they are merged and all printed in order.
   auto &semanticsCtx{ci.getSemanticsContext()};
   semanticsCtx.messages().Annex(std::move(ci.getParsing().messages()));
+  semanticsCtx.set_debugModuleWriter(ci.getInvocation().getDebugModuleDir());
 
   // Prepare semantics
-  ci.setSemantics(std::make_unique<Fortran::semantics::Semantics>(
-      semanticsCtx, *parseTree, ci.getInvocation().getDebugModuleDir()));
+  ci.setSemantics(std::make_unique<Fortran::semantics::Semantics>(semanticsCtx,
+                                                                  *parseTree));
   auto &semantics = ci.getSemantics();
+  semantics.set_hermeticModuleFileOutput(
+      ci.getInvocation().getHermeticModuleFileOutput());
 
   // Run semantic checks
   semantics.Perform();

diff --git a/flang/lib/Semantics/mod-file.cpp b/flang/lib/Semantics/mod-file.cpp
@@ -141,10 +141,26 @@ void ModFileWriter::Write(const Symbol &symbol) {
   auto ancestorName{ancestor ? ancestor->GetName().value().ToString() : ""s};
   auto path{context_.moduleDirectory() + '/' +
       ModFileName(symbol.name(), ancestorName, context_.moduleFileSuffix())};
-  PutSymbols(DEREF(symbol.scope()));
+
+  UnorderedSymbolSet hermeticModules;
+  hermeticModules.insert(symbol);
+  UnorderedSymbolSet additionalModules;
+  PutSymbols(DEREF(symbol.scope()),
+      hermeticModuleFileOutput_ ? &additionalModules : nullptr);
+  auto asStr{GetAsString(symbol)};
+  while (!additionalModules.empty()) {
+    for (auto ref : UnorderedSymbolSet{std::move(additionalModules)}) {
+      if (hermeticModules.insert(*ref).second &&
+          !ref->owner().IsIntrinsicModules()) {
+        PutSymbols(DEREF(ref->scope()), &additionalModules);
+        asStr += GetAsString(*ref);
+      }
+    }
+  }
+
   ModuleCheckSumType checkSum;
-  if (std::error_code error{WriteFile(
-          path, GetAsString(symbol), checkSum, context_.debugModuleWriter())}) {
+  if (std::error_code error{
+          WriteFile(path, asStr, checkSum, context_.debugModuleWriter())}) {
     context_.Say(
         symbol.name(), "Error writing %s: %s"_err_en_US, path, error.message());
   }
@@ -157,7 +173,7 @@ void ModFileWriter::WriteClosure(llvm::raw_ostream &out, const Symbol &symbol,
       !nonIntrinsicModulesWritten.insert(symbol).second) {
     return;
   }
-  PutSymbols(DEREF(symbol.scope()));
+  PutSymbols(DEREF(symbol.scope()), /*hermeticModules=*/nullptr);
   needsBuf_.clear(); // omit module checksums
   auto str{GetAsString(symbol)};
   for (auto depRef : std::move(usedNonIntrinsicModules_)) {
@@ -338,7 +354,8 @@ void ModFileWriter::PrepareRenamings(const Scope &scope) {
 }
 
 // Put out the visible symbols from scope.
-void ModFileWriter::PutSymbols(const Scope &scope) {
+void ModFileWriter::PutSymbols(
+    const Scope &scope, UnorderedSymbolSet *hermeticModules) {
   SymbolVector sorted;
   SymbolVector uses;
   auto &renamings{context_.moduleFileOutputRenamings()};
@@ -349,11 +366,16 @@ void ModFileWriter::PutSymbols(const Scope &scope) {
   // Write module files for dependencies first so that their
   // hashes are known.
   for (auto ref : modules) {
-    Write(*ref);
-    needs_ << ModHeader::need
-           << CheckSumString(ref->get<ModuleDetails>().moduleFileHash().value())
-           << (ref->owner().IsIntrinsicModules() ? " i " : " n ")
-           << ref->name().ToString() << '\n';
+    if (hermeticModules) {
+      hermeticModules->insert(*ref);
+    } else {
+      Write(*ref);
+      needs_ << ModHeader::need
+             << CheckSumString(
+                    ref->get<ModuleDetails>().moduleFileHash().value())
+             << (ref->owner().IsIntrinsicModules() ? " i " : " n ")
+             << ref->name().ToString() << '\n';
+    }
   }
   std::string buf; // stuff after CONTAINS in derived type
   llvm::raw_string_ostream typeBindings{buf};

diff --git a/flang/lib/Semantics/mod-file.h b/flang/lib/Semantics/mod-file.h
@@ -37,6 +37,10 @@ class ModFileWriter {
   bool WriteAll();
   void WriteClosure(llvm::raw_ostream &, const Symbol &,
       UnorderedSymbolSet &nonIntrinsicModulesWritten);
+  ModFileWriter &set_hermeticModuleFileOutput(bool yes = true) {
+    hermeticModuleFileOutput_ = yes;
+    return *this;
+  }
 
 private:
   SemanticsContext &context_;
@@ -57,13 +61,14 @@ class ModFileWriter {
   llvm::raw_string_ostream decls_{declsBuf_};
   llvm::raw_string_ostream contains_{containsBuf_};
   bool isSubmodule_{false};
+  bool hermeticModuleFileOutput_{false};
 
   void WriteAll(const Scope &);
   void WriteOne(const Scope &);
   void Write(const Symbol &);
   std::string GetAsString(const Symbol &);
   void PrepareRenamings(const Scope &);
-  void PutSymbols(const Scope &);
+  void PutSymbols(const Scope &, UnorderedSymbolSet *hermetic);
   // Returns true if a derived type with bindings and "contains" was emitted
   bool PutComponents(const Symbol &);
   void PutSymbol(llvm::raw_ostream &, const Symbol &);

diff --git a/flang/lib/Semantics/semantics.cpp b/flang/lib/Semantics/semantics.cpp
@@ -602,7 +602,9 @@ bool Semantics::Perform() {
       CanonicalizeCUDA(program_) &&
       CanonicalizeDirectives(context_.messages(), program_) &&
       PerformStatementSemantics(context_, program_) &&
-      ModFileWriter{context_}.WriteAll();
+      ModFileWriter{context_}
+          .set_hermeticModuleFileOutput(hermeticModuleFileOutput_)
+          .WriteAll();
 }
 
 void Semantics::EmitMessages(llvm::raw_ostream &os) {

diff --git a/flang/test/Semantics/modfile65.f90 b/flang/test/Semantics/modfile65.f90
@@ -0,0 +1,53 @@
+! RUN: %python %S/test_modfile.py %s %flang_fc1 -fhermetic-module-files
+module m1
+  integer, parameter :: n = 123
+end
+
+module m2
+  use m1
+end
+
+module m3
+  use m1, m => n
+end
+
+module m4
+  use m2
+  use m3
+end
+
+!Expect: m1.mod
+!module m1
+!integer(4),parameter::n=123_4
+!end
+
+!Expect: m2.mod
+!module m2
+!use m1,only:n
+!end
+!module m1
+!integer(4),parameter::n=123_4
+!end
+
+!Expect: m3.mod
+!module m3
+!use m1,only:m=>n
+!end
+!module m1
+!integer(4),parameter::n=123_4
+!end
+
+!Expect: m4.mod
+!module m4
+!use m2,only:n
+!use m3,only:m
+!end
+!module m2
+!use m1,only:n
+!end
+!module m3
+!use m1,only:m=>n
+!end
+!module m1
+!integer(4),parameter::n=123_4
+!end