[clang] [flang] [lld] [flang] Generate main only when a Fortran program statement is present (PR #89938)

David Truby via cfe-commits cfe-commits at lists.llvm.org
Wed Apr 24 07:52:02 PDT 2024


https://github.com/DavidTruby created https://github.com/llvm/llvm-project/pull/89938

This patch changes the behaviour for flang to only create and link to a
`main` entry point when the Fortran code has a program statement in it.

This means that flang-new can be used to link even when the program is
a mixed C/Fortran code with `main` present in C and no entry point
present in Fortran.


>From 88db34e906f6eb104f8d84fa9ad4f0aa49607c68 Mon Sep 17 00:00:00 2001
From: David Truby <david.truby at arm.com>
Date: Wed, 24 Apr 2024 14:35:23 +0000
Subject: [PATCH] [flang] Generate main only when a Fortran program statement
 is present

This patch changes the behaviour for flang to only create and link to a
`main` entry point when the Fortran code has a program statement in it.

This means that flang-new can be used to link even when the program is
a mixed C/Fortran code with `main` present in C and no entry point
present in Fortran.
---
 clang/include/clang/Driver/Options.td         |   6 -
 clang/lib/Driver/ToolChains/CommonArgs.cpp    | 110 +-----------------
 clang/lib/Driver/ToolChains/Flang.cpp         |   9 --
 flang/docs/FlangDriver.md                     |  32 +----
 .../Builder/Runtime/EnvironmentDefaults.h     |   3 +-
 .../flang/Optimizer/Builder/Runtime/Main.h    |  28 +++++
 flang/lib/Lower/Bridge.cpp                    |   5 +-
 flang/lib/Optimizer/Builder/CMakeLists.txt    |   1 +
 .../Builder/Runtime/EnvironmentDefaults.cpp   |   7 +-
 flang/lib/Optimizer/Builder/Runtime/Main.cpp  |  62 ++++++++++
 flang/runtime/CMakeLists.txt                  |   1 -
 flang/runtime/FortranMain/CMakeLists.txt      |  23 ----
 flang/runtime/FortranMain/Fortran_main.c      |  23 ----
 flang/test/CMakeLists.txt                     |   1 -
 flang/test/Driver/driver-help-hidden.f90      |   1 -
 flang/test/Driver/driver-help.f90             |   1 -
 flang/test/Driver/dynamic-linker.f90          |   2 -
 flang/test/Driver/emit-mlir.f90               |  10 ++
 flang/test/Driver/linker-flags.f90            |   8 --
 .../test/Driver/msvc-dependent-lib-flags.f90  |   4 -
 flang/test/Driver/no-duplicate-main.f90       |   2 -
 flang/tools/flang-driver/CMakeLists.txt       |   1 -
 lld/COFF/MinGW.cpp                            |   1 -
 23 files changed, 114 insertions(+), 227 deletions(-)
 create mode 100644 flang/include/flang/Optimizer/Builder/Runtime/Main.h
 create mode 100644 flang/lib/Optimizer/Builder/Runtime/Main.cpp
 delete mode 100644 flang/runtime/FortranMain/CMakeLists.txt
 delete mode 100644 flang/runtime/FortranMain/Fortran_main.c

diff --git a/clang/include/clang/Driver/Options.td b/clang/include/clang/Driver/Options.td
index 922bda721dc780..4b852b297a6b99 100644
--- a/clang/include/clang/Driver/Options.td
+++ b/clang/include/clang/Driver/Options.td
@@ -6582,12 +6582,6 @@ def J : JoinedOrSeparate<["-"], "J">,
   Group<gfortran_Group>,
   Alias<module_dir>;
 
-let Visibility = [FlangOption] in {
-def no_fortran_main : Flag<["-"], "fno-fortran-main">,
-  Visibility<[FlangOption]>, Group<f_Group>,
-  HelpText<"Do not include Fortran_main.a (provided by Flang) when linking">;
-} // let Visibility = [ FlangOption ]
-
 //===----------------------------------------------------------------------===//
 // FC1 Options
 //===----------------------------------------------------------------------===//
diff --git a/clang/lib/Driver/ToolChains/CommonArgs.cpp b/clang/lib/Driver/ToolChains/CommonArgs.cpp
index b65b96db16bd79..fec11c7e716fdf 100644
--- a/clang/lib/Driver/ToolChains/CommonArgs.cpp
+++ b/clang/lib/Driver/ToolChains/CommonArgs.cpp
@@ -1191,118 +1191,10 @@ bool tools::addOpenMPRuntime(const Compilation &C, ArgStringList &CmdArgs,
   return true;
 }
 
-/// Determines if --whole-archive is active in the list of arguments.
-static bool isWholeArchivePresent(const ArgList &Args) {
-  bool WholeArchiveActive = false;
-  for (auto *Arg : Args.filtered(options::OPT_Wl_COMMA)) {
-    if (Arg) {
-      for (StringRef ArgValue : Arg->getValues()) {
-        if (ArgValue == "--whole-archive")
-          WholeArchiveActive = true;
-        if (ArgValue == "--no-whole-archive")
-          WholeArchiveActive = false;
-      }
-    }
-  }
-
-  return WholeArchiveActive;
-}
-
-/// Determine if driver is invoked to create a shared object library (-static)
-static bool isSharedLinkage(const ArgList &Args) {
-  return Args.hasArg(options::OPT_shared);
-}
-
-/// Determine if driver is invoked to create a static object library (-shared)
-static bool isStaticLinkage(const ArgList &Args) {
-  return Args.hasArg(options::OPT_static);
-}
-
-/// Add Fortran runtime libs for MSVC
-static void addFortranRuntimeLibsMSVC(const ArgList &Args,
-                                      llvm::opt::ArgStringList &CmdArgs) {
-  unsigned RTOptionID = options::OPT__SLASH_MT;
-  if (auto *rtl = Args.getLastArg(options::OPT_fms_runtime_lib_EQ)) {
-    RTOptionID = llvm::StringSwitch<unsigned>(rtl->getValue())
-                     .Case("static", options::OPT__SLASH_MT)
-                     .Case("static_dbg", options::OPT__SLASH_MTd)
-                     .Case("dll", options::OPT__SLASH_MD)
-                     .Case("dll_dbg", options::OPT__SLASH_MDd)
-                     .Default(options::OPT__SLASH_MT);
-  }
-  switch (RTOptionID) {
-  case options::OPT__SLASH_MT:
-    CmdArgs.push_back("/WHOLEARCHIVE:Fortran_main.static.lib");
-    break;
-  case options::OPT__SLASH_MTd:
-    CmdArgs.push_back("/WHOLEARCHIVE:Fortran_main.static_dbg.lib");
-    break;
-  case options::OPT__SLASH_MD:
-    CmdArgs.push_back("/WHOLEARCHIVE:Fortran_main.dynamic.lib");
-    break;
-  case options::OPT__SLASH_MDd:
-    CmdArgs.push_back("/WHOLEARCHIVE:Fortran_main.dynamic_dbg.lib");
-    break;
-  }
-}
-
-// Add FortranMain runtime lib
-static void addFortranMain(const ToolChain &TC, const ArgList &Args,
-                           llvm::opt::ArgStringList &CmdArgs) {
-  // 0. Shared-library linkage
-  // If we are attempting to link a library, we should not add
-  // -lFortran_main.a to the link line, as the `main` symbol is not
-  // required for a library and should also be provided by one of
-  // the translation units of the code that this shared library
-  // will be linked against eventually.
-  if (isSharedLinkage(Args) || isStaticLinkage(Args)) {
-    return;
-  }
-
-  // 1. MSVC
-  if (TC.getTriple().isKnownWindowsMSVCEnvironment()) {
-    addFortranRuntimeLibsMSVC(Args, CmdArgs);
-    return;
-  }
-
-  // 2. GNU and similar
-  const Driver &D = TC.getDriver();
-  const char *FortranMainLinkFlag = "-lFortran_main";
-
-  // Warn if the user added `-lFortran_main` - this library is an implementation
-  // detail of Flang and should be handled automaticaly by the driver.
-  for (const char *arg : CmdArgs) {
-    if (strncmp(arg, FortranMainLinkFlag, strlen(FortranMainLinkFlag)) == 0)
-      D.Diag(diag::warn_drv_deprecated_custom)
-          << FortranMainLinkFlag
-          << "see the Flang driver documentation for correct usage";
-  }
-
-  // The --whole-archive option needs to be part of the link line to make
-  // sure that the main() function from Fortran_main.a is pulled in by the
-  // linker. However, it shouldn't be used if it's already active.
-  // TODO: Find an equivalent of `--whole-archive` for Darwin and AIX.
-  if (!isWholeArchivePresent(Args) && !TC.getTriple().isMacOSX() &&
-      !TC.getTriple().isOSAIX()) {
-    CmdArgs.push_back("--whole-archive");
-    CmdArgs.push_back(FortranMainLinkFlag);
-    CmdArgs.push_back("--no-whole-archive");
-    return;
-  }
-
-  CmdArgs.push_back(FortranMainLinkFlag);
-}
-
 /// Add Fortran runtime libs
 void tools::addFortranRuntimeLibs(const ToolChain &TC, const ArgList &Args,
                                   llvm::opt::ArgStringList &CmdArgs) {
-  // 1. Link FortranMain
-  // FortranMain depends on FortranRuntime, so needs to be listed first. If
-  // -fno-fortran-main has been passed, skip linking Fortran_main.a
-  if (!Args.hasArg(options::OPT_no_fortran_main))
-    addFortranMain(TC, Args, CmdArgs);
-
-  // 2. Link FortranRuntime and FortranDecimal
+  // Link FortranRuntime and FortranDecimal
   // These are handled earlier on Windows by telling the frontend driver to
   // add the correct libraries to link against as dependents in the object
   // file.
diff --git a/clang/lib/Driver/ToolChains/Flang.cpp b/clang/lib/Driver/ToolChains/Flang.cpp
index 6d93c1f3d7034a..8955b9fb653c2a 100644
--- a/clang/lib/Driver/ToolChains/Flang.cpp
+++ b/clang/lib/Driver/ToolChains/Flang.cpp
@@ -282,7 +282,6 @@ static void processVSRuntimeLibrary(const ToolChain &TC, const ArgList &Args,
   assert(TC.getTriple().isKnownWindowsMSVCEnvironment() &&
          "can only add VS runtime library on Windows!");
   // if -fno-fortran-main has been passed, skip linking Fortran_main.a
-  bool LinkFortranMain = !Args.hasArg(options::OPT_no_fortran_main);
   if (TC.getTriple().isKnownWindowsMSVCEnvironment()) {
     CmdArgs.push_back(Args.MakeArgString(
         "--dependent-lib=" + TC.getCompilerRTBasename(Args, "builtins")));
@@ -300,8 +299,6 @@ static void processVSRuntimeLibrary(const ToolChain &TC, const ArgList &Args,
   case options::OPT__SLASH_MT:
     CmdArgs.push_back("-D_MT");
     CmdArgs.push_back("--dependent-lib=libcmt");
-    if (LinkFortranMain)
-      CmdArgs.push_back("--dependent-lib=Fortran_main.static.lib");
     CmdArgs.push_back("--dependent-lib=FortranRuntime.static.lib");
     CmdArgs.push_back("--dependent-lib=FortranDecimal.static.lib");
     break;
@@ -309,8 +306,6 @@ static void processVSRuntimeLibrary(const ToolChain &TC, const ArgList &Args,
     CmdArgs.push_back("-D_MT");
     CmdArgs.push_back("-D_DEBUG");
     CmdArgs.push_back("--dependent-lib=libcmtd");
-    if (LinkFortranMain)
-      CmdArgs.push_back("--dependent-lib=Fortran_main.static_dbg.lib");
     CmdArgs.push_back("--dependent-lib=FortranRuntime.static_dbg.lib");
     CmdArgs.push_back("--dependent-lib=FortranDecimal.static_dbg.lib");
     break;
@@ -318,8 +313,6 @@ static void processVSRuntimeLibrary(const ToolChain &TC, const ArgList &Args,
     CmdArgs.push_back("-D_MT");
     CmdArgs.push_back("-D_DLL");
     CmdArgs.push_back("--dependent-lib=msvcrt");
-    if (LinkFortranMain)
-      CmdArgs.push_back("--dependent-lib=Fortran_main.dynamic.lib");
     CmdArgs.push_back("--dependent-lib=FortranRuntime.dynamic.lib");
     CmdArgs.push_back("--dependent-lib=FortranDecimal.dynamic.lib");
     break;
@@ -328,8 +321,6 @@ static void processVSRuntimeLibrary(const ToolChain &TC, const ArgList &Args,
     CmdArgs.push_back("-D_DEBUG");
     CmdArgs.push_back("-D_DLL");
     CmdArgs.push_back("--dependent-lib=msvcrtd");
-    if (LinkFortranMain)
-      CmdArgs.push_back("--dependent-lib=Fortran_main.dynamic_dbg.lib");
     CmdArgs.push_back("--dependent-lib=FortranRuntime.dynamic_dbg.lib");
     CmdArgs.push_back("--dependent-lib=FortranDecimal.dynamic_dbg.lib");
     break;
diff --git a/flang/docs/FlangDriver.md b/flang/docs/FlangDriver.md
index ac120b4ff09b6d..351595ac0afdb7 100644
--- a/flang/docs/FlangDriver.md
+++ b/flang/docs/FlangDriver.md
@@ -179,46 +179,20 @@ like this:
 
 ```
 $ flang -v -o example example.o
-"/usr/bin/ld" [...] example.o [...] "--whole-archive" "-lFortran_main"
-"--no-whole-archive" "-lFortranRuntime" "-lFortranDecimal" [...]
+"/usr/bin/ld" [...] example.o [...] "-lFortranRuntime" "-lFortranDecimal" [...]
 ```
 
 The automatically added libraries are:
 
-* `Fortran_main`: Provides the main entry point `main` that then invokes
-  `_QQmain` with the Fortran program unit.  This library has a dependency to
-  the `FortranRuntime` library.
 * `FortranRuntime`: Provides most of the Flang runtime library.
 * `FortranDecimal`: Provides operations for decimal numbers.
 
-The default is that, when using Flang as the linker, one of the Fortran
-translation units provides the program unit and therefore it is assumed that
-Fortran is the main code part (calling into C/C++ routines via `BIND (C)`
-interfaces).  When composing the linker commandline, Flang uses
-`--whole-archive` and `--no-whole-archive` (Windows: `/WHOLEARCHIVE:`,
-Darwin & AIX: *not implemented yet*) to make sure that all for `Fortran_main`
-is processed by the linker.  This is done to issue a proper error message when
-multiple definitions of `main` occur.  This happens, for instance, when linking
-a code that has a Fortran program unit with a C/C++ code that also defines a
-`main` function.  A user may be required to explicitly provide the C++ runtime
-libraries at link time (e.g., via `-lstdc++` for STL)
-
 If the code is C/C++ based and invokes Fortran routines, one can either use Clang
 or Flang as the linker driver.  If Clang is used, it will automatically all
 required runtime libraries needed by C++ (e.g., for STL) to the linker invocation.
 In this case, one has to explicitly provide the Fortran runtime libraries
-`FortranRuntime` and/or `FortranDecimal`.  An alternative is to use Flang to link
-and use the `-fno-fortran-main` flag.  This flag removes
-`Fortran_main` from the linker stage and hence requires one of the C/C++
-translation units to provide a definition of the `main` function. In this case,
-it may be required to explicitly supply C++ runtime libraries as mentioned above.
-
-When creating shared or static libraries using Flang with `-shared` or `-static`
-flag, Fortran_main is automatically removed from the linker stage (i.e.,
-`-fno-fortran-main` is on by default).  It is assumed that when creating a
-static or shared library, the generated library does not need a `main`
-function, as a final link stage will occur that will provide the `Fortran_main`
-library when creating the final executable.
+`FortranRuntime` and/or `FortranDecimal`.  An alternative is to use Flang to link.
+In this case, it may be required to explicitly supply C++ runtime libraries.
 
 On Darwin, the logical root where the system libraries are located (sysroot)
 must be specified. This can be done with the CMake build flag `DEFAULT_SYSROOT`
diff --git a/flang/include/flang/Optimizer/Builder/Runtime/EnvironmentDefaults.h b/flang/include/flang/Optimizer/Builder/Runtime/EnvironmentDefaults.h
index 18a24bad396044..216d3bcec137e1 100755
--- a/flang/include/flang/Optimizer/Builder/Runtime/EnvironmentDefaults.h
+++ b/flang/include/flang/Optimizer/Builder/Runtime/EnvironmentDefaults.h
@@ -22,6 +22,7 @@
 
 namespace fir {
 class FirOpBuilder;
+class GlobalOp;
 } // namespace fir
 
 namespace mlir {
@@ -37,7 +38,7 @@ namespace fir::runtime {
 /// Create the list of environment variable defaults for the runtime to set. The
 /// form of the generated list is defined in the runtime header file
 /// environment-default-list.h
-void genEnvironmentDefaults(
+fir::GlobalOp genEnvironmentDefaults(
     fir::FirOpBuilder &builder, mlir::Location loc,
     const std::vector<Fortran::lower::EnvironmentDefault> &envDefaults);
 
diff --git a/flang/include/flang/Optimizer/Builder/Runtime/Main.h b/flang/include/flang/Optimizer/Builder/Runtime/Main.h
new file mode 100644
index 00000000000000..62faf46e1fc778
--- /dev/null
+++ b/flang/include/flang/Optimizer/Builder/Runtime/Main.h
@@ -0,0 +1,28 @@
+//===-- Main.h - generate main runtime API calls ----------------*- C++ -*-===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef FORTRAN_OPTIMIZER_BUILDER_RUNTIME_MAIN_H
+#define FORTRAN_OPTIMIZER_BUILDER_RUNTIME_MAIN_H
+
+namespace mlir {
+class Location;
+} // namespace mlir
+
+namespace fir {
+class FirOpBuilder;
+class GlobalOp;
+} // namespace fir
+
+namespace fir::runtime {
+
+void genMain(fir::FirOpBuilder &builder, mlir::Location loc,
+             fir::GlobalOp &env);
+
+}
+
+#endif // FORTRAN_OPTIMIZER_BUILDER_RUNTIME_MAIN_H
diff --git a/flang/lib/Lower/Bridge.cpp b/flang/lib/Lower/Bridge.cpp
index 8b62fe8c022f80..afb5496ff8bc29 100644
--- a/flang/lib/Lower/Bridge.cpp
+++ b/flang/lib/Lower/Bridge.cpp
@@ -36,6 +36,7 @@
 #include "flang/Optimizer/Builder/Runtime/Character.h"
 #include "flang/Optimizer/Builder/Runtime/Derived.h"
 #include "flang/Optimizer/Builder/Runtime/EnvironmentDefaults.h"
+#include "flang/Optimizer/Builder/Runtime/Main.h"
 #include "flang/Optimizer/Builder/Runtime/Ragged.h"
 #include "flang/Optimizer/Builder/Runtime/Stop.h"
 #include "flang/Optimizer/Builder/Todo.h"
@@ -359,8 +360,10 @@ class FirConverter : public Fortran::lower::AbstractConverter {
         // not need to be generated even if no defaults are specified.
         // However, generating main or changing when the runtime reads
         // environment variables is required to do so.
-        fir::runtime::genEnvironmentDefaults(*builder, toLocation(),
+        auto env = fir::runtime::genEnvironmentDefaults(*builder, toLocation(),
                                              bridge.getEnvironmentDefaults());
+
+        fir::runtime::genMain(*builder, toLocation(), env);
       });
 
     finalizeOpenACCLowering();
diff --git a/flang/lib/Optimizer/Builder/CMakeLists.txt b/flang/lib/Optimizer/Builder/CMakeLists.txt
index 06339b116cd899..95f19ed4dfbdf8 100644
--- a/flang/lib/Optimizer/Builder/CMakeLists.txt
+++ b/flang/lib/Optimizer/Builder/CMakeLists.txt
@@ -24,6 +24,7 @@ add_flang_library(FIRBuilder
   Runtime/Inquiry.cpp
   Runtime/Intrinsics.cpp
   Runtime/Numeric.cpp
+  Runtime/Main.cpp
   Runtime/Pointer.cpp
   Runtime/Ragged.cpp
   Runtime/Reduction.cpp
diff --git a/flang/lib/Optimizer/Builder/Runtime/EnvironmentDefaults.cpp b/flang/lib/Optimizer/Builder/Runtime/EnvironmentDefaults.cpp
index a11b9339681e3b..6e280ac0c06cd2 100755
--- a/flang/lib/Optimizer/Builder/Runtime/EnvironmentDefaults.cpp
+++ b/flang/lib/Optimizer/Builder/Runtime/EnvironmentDefaults.cpp
@@ -13,7 +13,7 @@
 #include "flang/Optimizer/Support/InternalNames.h"
 #include "llvm/ADT/ArrayRef.h"
 
-void fir::runtime::genEnvironmentDefaults(
+fir::GlobalOp fir::runtime::genEnvironmentDefaults(
     fir::FirOpBuilder &builder, mlir::Location loc,
     const std::vector<Fortran::lower::EnvironmentDefault> &envDefaults) {
   std::string envDefaultListPtrName =
@@ -34,14 +34,13 @@ void fir::runtime::genEnvironmentDefaults(
 
   // If no defaults were specified, initialize with a null pointer.
   if (envDefaults.empty()) {
-    builder.createGlobalConstant(
+    return builder.createGlobalConstant(
         loc, envDefaultListRefTy, envDefaultListPtrName,
         [&](fir::FirOpBuilder &builder) {
           mlir::Value nullVal =
               builder.createNullConstant(loc, envDefaultListRefTy);
           builder.create<fir::HasValueOp>(loc, nullVal);
         });
-    return;
   }
 
   // Create the Item list.
@@ -99,7 +98,7 @@ void fir::runtime::genEnvironmentDefaults(
       envDefaultListBuilder, linkOnce);
 
   // Define the pointer to the list used by the runtime.
-  builder.createGlobalConstant(
+  return builder.createGlobalConstant(
       loc, envDefaultListRefTy, envDefaultListPtrName,
       [&](fir::FirOpBuilder &builder) {
         mlir::Value addr = builder.create<fir::AddrOfOp>(
diff --git a/flang/lib/Optimizer/Builder/Runtime/Main.cpp b/flang/lib/Optimizer/Builder/Runtime/Main.cpp
new file mode 100644
index 00000000000000..93d082b8094eb6
--- /dev/null
+++ b/flang/lib/Optimizer/Builder/Runtime/Main.cpp
@@ -0,0 +1,62 @@
+//===-- Main.cpp - generate main runtime API calls ----------------*- C++
+//-*-===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "flang/Optimizer/Builder/Runtime/Main.h"
+#include "flang/Optimizer/Builder/BoxValue.h"
+#include "flang/Optimizer/Builder/FIRBuilder.h"
+#include "flang/Optimizer/Builder/Runtime/RTBuilder.h"
+#include "flang/Optimizer/Dialect/FIROps.h"
+#include "flang/Optimizer/Dialect/FIRType.h"
+#include "flang/Runtime/main.h"
+#include "flang/Runtime/stop.h"
+
+using namespace Fortran::runtime;
+
+/// Create a `int main(...)` that calls the Fortran entry point
+void fir::runtime::genMain(fir::FirOpBuilder &builder, mlir::Location loc,
+                           fir::GlobalOp &env) {
+  auto *context = builder.getContext();
+  auto argcTy = builder.getDefaultIntegerType();
+  auto ptrTy = mlir::LLVM::LLVMPointerType::get(context);
+
+  // void ProgramStart(int argc, char** argv, char** envp, _QQEnvironmentDefaults* env)
+  auto startFn = builder.createFunction(
+      loc, RTNAME_STRING(ProgramStart),
+      mlir::FunctionType::get(context, {argcTy, ptrTy, ptrTy, ptrTy}, {}));
+  // void ProgramStop()
+  auto stopFn =
+      builder.createFunction(loc, RTNAME_STRING(ProgramEndStatement),
+                             mlir::FunctionType::get(context, {}, {}));
+
+  // int main(int argc, char** argv, char** envp)
+  auto mainFn = builder.createFunction(
+      loc, "main",
+      mlir::FunctionType::get(context, {argcTy, ptrTy, ptrTy}, argcTy));
+  // void _QQmain()
+  auto qqMainFn = builder.createFunction(loc, "_QQmain",
+                                      mlir::FunctionType::get(context, {}, {}));
+
+  mainFn.setPublic();
+
+  auto *block = mainFn.addEntryBlock();
+  mlir::OpBuilder::InsertionGuard insertGuard(builder);
+  builder.setInsertionPointToStart(block);
+
+  llvm::SmallVector<mlir::Value, 4> args (block->getArguments());
+  auto envAddr =
+      builder.create<fir::AddrOfOp>(loc, env.getType(), env.getSymbol());
+  args.push_back(envAddr);
+
+  builder.create<fir::CallOp>(loc, startFn, args);
+  builder.create<fir::CallOp>(loc, qqMainFn);
+  builder.create<fir::CallOp>(loc, stopFn);
+
+  mlir::Value ret = builder.createIntegerConstant(loc, argcTy, 0);
+  builder.create<mlir::func::ReturnOp>(loc, ret);
+}
diff --git a/flang/runtime/CMakeLists.txt b/flang/runtime/CMakeLists.txt
index bdd0e07bbfd4d1..9f25c5dfcad11d 100644
--- a/flang/runtime/CMakeLists.txt
+++ b/flang/runtime/CMakeLists.txt
@@ -103,7 +103,6 @@ append(${NO_LTO_FLAGS} CMAKE_CXX_FLAGS)
 add_definitions(-U_GLIBCXX_ASSERTIONS)
 add_definitions(-U_LIBCPP_ENABLE_ASSERTIONS)
 
-add_subdirectory(FortranMain)
 add_subdirectory(Float128Math)
 
 set(sources
diff --git a/flang/runtime/FortranMain/CMakeLists.txt b/flang/runtime/FortranMain/CMakeLists.txt
deleted file mode 100644
index deb7bd10acf512..00000000000000
--- a/flang/runtime/FortranMain/CMakeLists.txt
+++ /dev/null
@@ -1,23 +0,0 @@
-add_flang_library(Fortran_main STATIC INSTALL_WITH_TOOLCHAIN
-  Fortran_main.c
-)
-if (DEFINED MSVC)
-  set(CMAKE_MSVC_RUNTIME_LIBRARY MultiThreaded)
-  add_flang_library(Fortran_main.static STATIC INSTALL_WITH_TOOLCHAIN
-    Fortran_main.c
-  )
-  set(CMAKE_MSVC_RUNTIME_LIBRARY MultiThreadedDLL)
-  add_flang_library(Fortran_main.dynamic STATIC INSTALL_WITH_TOOLCHAIN
-    Fortran_main.c
-  )
-  set(CMAKE_MSVC_RUNTIME_LIBRARY MultiThreadedDebug)
-  add_flang_library(Fortran_main.static_dbg STATIC INSTALL_WITH_TOOLCHAIN
-    Fortran_main.c
-  )
-  set(CMAKE_MSVC_RUNTIME_LIBRARY MultiThreadedDebugDLL)
-  add_flang_library(Fortran_main.dynamic_dbg STATIC INSTALL_WITH_TOOLCHAIN
-    Fortran_main.c
-  )
-  add_dependencies(Fortran_main Fortran_main.static Fortran_main.dynamic
-    Fortran_main.static_dbg Fortran_main.dynamic_dbg)
-endif()
diff --git a/flang/runtime/FortranMain/Fortran_main.c b/flang/runtime/FortranMain/Fortran_main.c
deleted file mode 100644
index 5d3eaced001ebc..00000000000000
--- a/flang/runtime/FortranMain/Fortran_main.c
+++ /dev/null
@@ -1,23 +0,0 @@
-//===-- runtime/FortranMain/Fortran_main.c --------------------------------===//
-//
-// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
-// See https://llvm.org/LICENSE.txt for license information.
-// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
-//
-//===----------------------------------------------------------------------===//
-
-#include "flang/Runtime/main.h"
-#include "flang/Runtime/stop.h"
-
-/* main entry into PROGRAM */
-void _QQmain(void);
-
-extern const struct EnvironmentDefaultList *_QQEnvironmentDefaults;
-
-/* C main stub */
-int main(int argc, const char *argv[], const char *envp[]) {
-  RTNAME(ProgramStart)(argc, argv, envp, _QQEnvironmentDefaults);
-  _QQmain();
-  RTNAME(ProgramEndStatement)();
-  return 0;
-}
diff --git a/flang/test/CMakeLists.txt b/flang/test/CMakeLists.txt
index 7d96a72e5f36d6..7e036ad539dfcd 100644
--- a/flang/test/CMakeLists.txt
+++ b/flang/test/CMakeLists.txt
@@ -62,7 +62,6 @@ set(FLANG_TEST_DEPENDS
   llvm-readobj
   split-file
   FortranRuntime
-  Fortran_main
   FortranDecimal
 )
 if (LLVM_ENABLE_PLUGINS AND NOT WIN32)
diff --git a/flang/test/Driver/driver-help-hidden.f90 b/flang/test/Driver/driver-help-hidden.f90
index b5bb0f1c1b2560..706b2cb6c2452c 100644
--- a/flang/test/Driver/driver-help-hidden.f90
+++ b/flang/test/Driver/driver-help-hidden.f90
@@ -63,7 +63,6 @@
 ! CHECK-NEXT:                         Select Windows run-time library
 ! CHECK-NEXT: -fno-automatic          Implies the SAVE attribute for non-automatic local objects in subprograms unless RECURSIVE
 ! CHECK-NEXT: -fno-color-diagnostics  Disable colors in diagnostics
-! CHECK-NEXT: -fno-fortran-main       Do not include Fortran_main.a (provided by Flang) when linking
 ! CHECK-NEXT: -fno-integrated-as      Disable the integrated assembler
 ! CHECK-NEXT: -fno-lto                Disable LTO mode (default)
 ! CHECK-NEXT: -fno-ppc-native-vector-element-order
diff --git a/flang/test/Driver/driver-help.f90 b/flang/test/Driver/driver-help.f90
index 0b0a493baf07f7..85ba8c0bdcbe27 100644
--- a/flang/test/Driver/driver-help.f90
+++ b/flang/test/Driver/driver-help.f90
@@ -55,7 +55,6 @@
 ! HELP-NEXT:                         Select Windows run-time library
 ! HELP-NEXT: -fno-automatic          Implies the SAVE attribute for non-automatic local objects in subprograms unless RECURSIVE
 ! HELP-NEXT: -fno-color-diagnostics  Disable colors in diagnostics
-! HELP-NEXT: -fno-fortran-main       Do not include Fortran_main.a (provided by Flang) when linking
 ! HELP-NEXT: -fno-integrated-as      Disable the integrated assembler
 ! HELP-NEXT: -fno-lto                Disable LTO mode (default)
 ! HELP-NEXT: -fno-ppc-native-vector-element-order
diff --git a/flang/test/Driver/dynamic-linker.f90 b/flang/test/Driver/dynamic-linker.f90
index 7c3f1b5a53fe48..6d5c443ab75cb3 100644
--- a/flang/test/Driver/dynamic-linker.f90
+++ b/flang/test/Driver/dynamic-linker.f90
@@ -16,7 +16,6 @@
 ! GNU-LINKER-OPTIONS-SAME: "-shared"
 ! GNU-LINKER-OPTIONS-SAME: "-static"
 ! GNU-LINKER-OPTIONS-SAME: "-rpath" "/path/to/dir"
-! GNU-LINKER-OPTIONS-NOT: "-lFortran_main.a"
 
 ! RDYNAMIC-LINKER-OPTION: "{{.*}}ld"
 ! RDYNAMIC-LINKER-OPTION-SAME: "-export-dynamic"
@@ -25,4 +24,3 @@
 ! MSVC-LINKER-OPTIONS: "{{.*}}link{{(.exe)?}}"
 ! MSVC-LINKER-OPTIONS-SAME: "-dll"
 ! MSVC-LINKER-OPTIONS-SAME: "-rpath" "/path/to/dir"
-! MSVC-LINKER-OPTIONS-NOT: "/WHOLEARCHIVE:Fortran_main"
diff --git a/flang/test/Driver/emit-mlir.f90 b/flang/test/Driver/emit-mlir.f90
index 191ee13396ef93..83bb8fc1eddcd2 100644
--- a/flang/test/Driver/emit-mlir.f90
+++ b/flang/test/Driver/emit-mlir.f90
@@ -19,6 +19,16 @@
 ! CHECK-NEXT:  %[[VAL_0:.*]] = fir.zero_bits !fir.ref<tuple<i[[int_size]], !fir.ref<!fir.array<0xtuple<!fir.ref<i8>, !fir.ref<i8>>>>>>
 ! CHECK-NEXT: fir.has_value  %[[VAL_0]] : !fir.ref<tuple<i[[int_size]], !fir.ref<!fir.array<0xtuple<!fir.ref<i8>, !fir.ref<i8>>>>>>
 ! CHECK-NEXT: }
+! CHECK-NEXT: func.func private @_FortranAProgramStart(i32, !llvm.ptr, !llvm.ptr, !llvm.ptr)
+! CHECK-NEXT: func.func private @_FortranAProgramEndStatement()
+! CHECK-NEXT: func.func @main(%arg0: i32, %arg1: !llvm.ptr, %arg2: !llvm.ptr) -> i32 {
+! CHECK-NEXT: %c0_i32 = arith.constant 0 : i32
+! CHECK-NEXT: %0 = fir.address_of(@_QQEnvironmentDefaults) : !fir.ref<tuple<i32, !fir.ref<!fir.array<0xtuple<!fir.ref<i8>, !fir.ref<i8>>>>>>
+! CHECK-NEXT: ir.call @_FortranAProgramStart(%arg0, %arg1, %arg2, %0) {{.*}} : (i32, !llvm.ptr, !llvm.ptr, !fir.ref<tuple<i32, !fir.ref<!fir.array<0xtuple<!fir.ref<i8>, !fir.ref<i8>>>>>>) 
+! CHECK-NEXT: fir.call @_QQmain() fastmath<contract> : () -> ()
+! CHECK-NEXT: fir.call @_FortranAProgramEndStatement() {{.*}} : () -> ()
+! CHECK-NEXT: return %c0_i32 : i32
+! CHECK-NEXT: }
 ! CHECK-NEXT: }
 
 end program
diff --git a/flang/test/Driver/linker-flags.f90 b/flang/test/Driver/linker-flags.f90
index 4d3d528b5e99e0..02e217494f818f 100644
--- a/flang/test/Driver/linker-flags.f90
+++ b/flang/test/Driver/linker-flags.f90
@@ -11,7 +11,6 @@
 ! RUN: %flang -### --target=x86_64-unknown-dragonfly %S/Inputs/hello.f90 2>&1 | FileCheck %s --check-prefixes=CHECK,UNIX,UNIX-F128%f128-lib
 ! RUN: %flang -### --target=x86_64-unknown-haiku %S/Inputs/hello.f90 2>&1 | FileCheck %s --check-prefixes=CHECK,HAIKU,HAIKU-F128%f128-lib
 ! RUN: %flang -### --target=x86_64-windows-gnu %S/Inputs/hello.f90 2>&1 | FileCheck %s --check-prefixes=CHECK,MINGW,MINGW-F128%f128-lib
-! RUN: %flang -### --target=aarch64-unknown-linux-gnu %S/Inputs/hello.f90 -lFortran_main 2>&1 | FileCheck %s --check-prefixes=DEPRECATED
 
 ! NOTE: Clang's driver library, clangDriver, usually adds 'oldnames' on Windows,
 !       but it is not needed when compiling Fortran code and they might bring in
@@ -29,7 +28,6 @@
 !       executable and may find the GNU linker from MinGW or Cygwin.
 ! UNIX-LABEL:  "{{.*}}ld{{(\.exe)?}}"
 ! UNIX-SAME: "[[object_file]]"
-! UNIX-SAME: "--whole-archive" "-lFortran_main" "--no-whole-archive"
 ! UNIX-F128NONE-NOT: FortranFloat128Math
 ! SOLARIS-F128NONE-NOT: FortranFloat128Math
 ! UNIX-F128LIBQUADMATH-SAME: "-lFortranFloat128Math" "--as-needed" "-lquadmath" "--no-as-needed"
@@ -38,7 +36,6 @@
 
 ! DARWIN-LABEL:  "{{.*}}ld{{(\.exe)?}}"
 ! DARWIN-SAME: "[[object_file]]"
-! DARWIN-SAME: -lFortran_main
 ! DARWIN-F128NONE-NOT: FortranFloat128Math
 ! DARWIN-F128LIBQUADMATH-SAME: "-lFortranFloat128Math" "--as-needed" "-lquadmath" "--no-as-needed"
 ! DARWIN-SAME: -lFortranRuntime
@@ -46,14 +43,12 @@
 
 ! HAIKU-LABEL:  "{{.*}}ld{{(\.exe)?}}"
 ! HAIKU-SAME: "[[object_file]]"
-! HAIKU-SAME: "--whole-archive" "-lFortran_main" "--no-whole-archive"
 ! HAIKU-F128NONE-NOT: FortranFloat128Math
 ! HAIKU-F128LIBQUADMATH-SAME: "-lFortranFloat128Math" "--as-needed" "-lquadmath" "--no-as-needed"
 ! HAIKU-SAME: "-lFortranRuntime" "-lFortranDecimal"
 
 ! MINGW-LABEL:  "{{.*}}ld{{(\.exe)?}}"
 ! MINGW-SAME: "[[object_file]]"
-! MINGW-SAME: -lFortran_main
 ! MINGW-F128NONE-NOT: FortranFloat128Math
 ! MINGW-F128LIBQUADMATH-SAME: "-lFortranFloat128Math" "--as-needed" "-lquadmath" "--no-as-needed"
 ! MINGW-SAME: -lFortranRuntime
@@ -66,6 +61,3 @@
 ! MSVC-LABEL: link
 ! MSVC-SAME: /subsystem:console
 ! MSVC-SAME: "[[object_file]]"
-
-! Check that we warn when using -lFortran_main
-! DEPRECATED: warning: argument '-lFortran_main' is deprecated, see the Flang driver documentation for correct usage [-Wdeprecated]
diff --git a/flang/test/Driver/msvc-dependent-lib-flags.f90 b/flang/test/Driver/msvc-dependent-lib-flags.f90
index 6cfc969e92b20a..765917f07d8e72 100644
--- a/flang/test/Driver/msvc-dependent-lib-flags.f90
+++ b/flang/test/Driver/msvc-dependent-lib-flags.f90
@@ -7,7 +7,6 @@
 ! MSVC-SAME: --dependent-lib=clang_rt.builtins.lib
 ! MSVC-SAME: -D_MT
 ! MSVC-SAME: --dependent-lib=libcmt
-! MSVC-SAME: --dependent-lib=Fortran_main.static.lib
 ! MSVC-SAME: --dependent-lib=FortranRuntime.static.lib
 ! MSVC-SAME: --dependent-lib=FortranDecimal.static.lib
 
@@ -16,7 +15,6 @@
 ! MSVC-DEBUG-SAME: -D_MT
 ! MSVC-DEBUG-SAME: -D_DEBUG
 ! MSVC-DEBUG-SAME: --dependent-lib=libcmtd
-! MSVC-DEBUG-SAME: --dependent-lib=Fortran_main.static_dbg.lib
 ! MSVC-DEBUG-SAME: --dependent-lib=FortranRuntime.static_dbg.lib
 ! MSVC-DEBUG-SAME: --dependent-lib=FortranDecimal.static_dbg.lib
 
@@ -25,7 +23,6 @@
 ! MSVC-DLL-SAME: -D_MT
 ! MSVC-DLL-SAME: -D_DLL
 ! MSVC-DLL-SAME: --dependent-lib=msvcrt
-! MSVC-DLL-SAME: --dependent-lib=Fortran_main.dynamic.lib
 ! MSVC-DLL-SAME: --dependent-lib=FortranRuntime.dynamic.lib
 ! MSVC-DLL-SAME: --dependent-lib=FortranDecimal.dynamic.lib
 
@@ -35,6 +32,5 @@
 ! MSVC-DLL-DEBUG-SAME: -D_DEBUG
 ! MSVC-DLL-DEBUG-SAME: -D_DLL
 ! MSVC-DLL-DEBUG-SAME: --dependent-lib=msvcrtd
-! MSVC-DLL-DEBUG-SAME: --dependent-lib=Fortran_main.dynamic_dbg.lib
 ! MSVC-DLL-DEBUG-SAME: --dependent-lib=FortranRuntime.dynamic_dbg.lib
 ! MSVC-DLL-DEBUG-SAME: --dependent-lib=FortranDecimal.dynamic_dbg.lib
diff --git a/flang/test/Driver/no-duplicate-main.f90 b/flang/test/Driver/no-duplicate-main.f90
index 88f4430828e090..b0bb6c2a2fefbd 100644
--- a/flang/test/Driver/no-duplicate-main.f90
+++ b/flang/test/Driver/no-duplicate-main.f90
@@ -4,8 +4,6 @@
 ! RUN: %flang -o %t -c %s
 ! RUN: not %flang -o %t.exe %t %t.c-object 2>&1
 
-! RUN: %flang -fno-fortran-main -o %t.exe %t %t.c-object 2>&1
-
 ! TODO: potentially add further checks to ensure that proper
 !       linker error messages are detected and checked via
 !       FileCheck.
diff --git a/flang/tools/flang-driver/CMakeLists.txt b/flang/tools/flang-driver/CMakeLists.txt
index 3ce8b407450d24..ce30ecff028dcf 100644
--- a/flang/tools/flang-driver/CMakeLists.txt
+++ b/flang/tools/flang-driver/CMakeLists.txt
@@ -21,7 +21,6 @@ add_flang_tool(flang-new
   # unable to generate executables.
   FortranRuntime
   FortranDecimal
-  Fortran_main
 )
 
 target_link_libraries(flang-new
diff --git a/lld/COFF/MinGW.cpp b/lld/COFF/MinGW.cpp
index e46f5277a8c365..29c01da9e28f6d 100644
--- a/lld/COFF/MinGW.cpp
+++ b/lld/COFF/MinGW.cpp
@@ -50,7 +50,6 @@ AutoExporter::AutoExporter(
       "libclang_rt.profile-x86_64",
       "libc++",
       "libc++abi",
-      "libFortran_main",
       "libFortranRuntime",
       "libFortranDecimal",
       "libunwind",



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