[Driver] Pass Classic Flang libraries to the linker correctly

In LLVM 15, the Fortran and OpenMP runtime libraries are added to the linker
command line using common methods (addFortranRuntime* and addOpenMPRuntime*).
This commit adds Classic Flang awareness to addFortranRuntime*, so that
Classic Flang doesn't attempt to link with LLVM Flang libraries. Re-using
the same methods as Clang and LLVM Flang also helps reduce downstream delta.
A Classic Flang test is added to ensure that the linker command is constructed
correctly.

LLVM 19 porting note: This commit has been amended to add back the
-fno-fortran-main option that was deleted in upstream commit 8d53866.

Author: bryanpkc

clang/include/clang/Driver/Options.td

@@ -6776,6 +6776,12 @@ def fhermetic_module_files : Flag<["-"], "fhermetic-module-files">, Group<f_Grou
 def J : JoinedOrSeparate<["-"], "J">,
   Flags<[RenderJoined]>,
   Group<gfortran_Group>;
+
+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 ]
 #else
 def J : JoinedOrSeparate<["-"], "J">,
   Flags<[RenderJoined]>, Visibility<[FlangOption, FC1Option]>,

clang/lib/Driver/ToolChain.cpp

@@ -1325,42 +1325,26 @@ void ToolChain::AddCCKextLibArgs(const ArgList &Args,
 
 #ifdef ENABLE_CLASSIC_FLANG
 void ToolChain::AddFortranStdlibLibArgs(const ArgList &Args,
-                                    ArgStringList &CmdArgs) const {
- bool staticFlangLibs = false;
- bool useOpenMP = false;
-
+                                        ArgStringList &CmdArgs) const {
+  bool StaticFlangLibs = false;
   if (Args.hasArg(options::OPT_staticFlangLibs)) {
-    for (auto *A: Args.filtered(options::OPT_staticFlangLibs)) {
-      A->claim();
-      staticFlangLibs = true;
-    }
-  }
-
-  Arg *A = Args.getLastArg(options::OPT_mp, options::OPT_nomp,
-                           options::OPT_fopenmp, options::OPT_fno_openmp);
-  if (A &&
-      (A->getOption().matches(options::OPT_mp) ||
-       A->getOption().matches(options::OPT_fopenmp))) {
-      useOpenMP = true;
+    StaticFlangLibs = true;
+    Args.ClaimAllArgs(options::OPT_staticFlangLibs);
   }
 
-  if (staticFlangLibs)
+  if (StaticFlangLibs && !Args.hasArg(options::OPT_static))
     CmdArgs.push_back("-Bstatic");
   CmdArgs.push_back("-lflang");
   CmdArgs.push_back("-lflangrti");
   CmdArgs.push_back("-lpgmath");
-  if (useOpenMP)
-    CmdArgs.push_back("-lomp");
-  if (staticFlangLibs)
+  if (StaticFlangLibs && !Args.hasArg(options::OPT_static))
     CmdArgs.push_back("-Bdynamic");
 
-  CmdArgs.push_back("-lm");
+  // Always link Fortran executables with pthreads.
+  CmdArgs.push_back("-lpthread");
 
   if (!Triple.isOSDarwin())
     CmdArgs.push_back("-lrt");
-
-  // Allways link Fortran executables with Pthreads
-  CmdArgs.push_back("-lpthread");
 }
 #endif
 

clang/lib/Driver/ToolChains/CommonArgs.cpp

@@ -1273,7 +1273,11 @@ bool tools::addOpenMPRuntime(const Compilation &C, ArgStringList &CmdArgs,
                              bool ForceStaticHostRuntime, bool IsOffloadingHost,
                              bool GompNeedsRT) {
   if (!Args.hasFlag(options::OPT_fopenmp, options::OPT_fopenmp_EQ,
-                    options::OPT_fno_openmp, false))
+                    options::OPT_fno_openmp, false)
+#ifdef ENABLE_CLASSIC_FLANG
+      && !Args.hasFlag(options::OPT_mp, options::OPT_nomp, false)
+#endif
+     )
     return false;
 
   Driver::OpenMPRuntimeKind RTKind = TC.getDriver().getOpenMPRuntime(Args);
@@ -1323,6 +1327,12 @@ bool tools::addOpenMPRuntime(const Compilation &C, ArgStringList &CmdArgs,
 /// Add Fortran runtime libs
 void tools::addFortranRuntimeLibs(const ToolChain &TC, const ArgList &Args,
                                   llvm::opt::ArgStringList &CmdArgs) {
+#ifdef ENABLE_CLASSIC_FLANG
+  if (needFortranLibs(TC.getDriver(), Args))
+    TC.AddFortranStdlibLibArgs(Args, CmdArgs);
+  else
+    Args.ClaimAllArgs(options::OPT_noFlangLibs);
+#else
   // 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
@@ -1342,6 +1352,7 @@ void tools::addFortranRuntimeLibs(const ToolChain &TC, const ArgList &Args,
     CmdArgs.push_back("-lFortranRuntime");
     CmdArgs.push_back("-lFortranDecimal");
   }
+#endif
 }
 
 void tools::addFortranRuntimeLibraryPath(const ToolChain &TC,

clang/lib/Driver/ToolChains/Darwin.cpp

@@ -721,18 +721,6 @@ void darwin::Linker::ConstructJob(Compilation &C, const JobAction &JA,
   if (getToolChain().ShouldLinkCXXStdlib(Args))
     getToolChain().AddCXXStdlibLibArgs(Args, CmdArgs);
 
-#ifdef ENABLE_CLASSIC_FLANG
-  // Add Fortran runtime libraries
-  if (needFortranLibs(getToolChain().getDriver(), Args)) {
-    getToolChain().AddFortranStdlibLibArgs(Args, CmdArgs);
-  } else {
-    // Claim "no Flang libraries" arguments if any
-    for (auto Arg : Args.filtered(options::OPT_noFlangLibs)) {
-      Arg->claim();
-    }
-  }
-#endif
-
   bool NoStdOrDefaultLibs =
       Args.hasArg(options::OPT_nostdlib, options::OPT_nodefaultlibs);
   bool ForceLinkBuiltins = Args.hasArg(options::OPT_fapple_link_rtlib);

clang/lib/Driver/ToolChains/Gnu.cpp

@@ -550,18 +550,6 @@ void tools::gnutools::Linker::ConstructJob(Compilation &C, const JobAction &JA,
   // The profile runtime also needs access to system libraries.
   getToolChain().addProfileRTLibs(Args, CmdArgs);
 
-#ifdef ENABLE_CLASSIC_FLANG
-  // Add Fortran runtime libraries
-  if (needFortranLibs(D, Args)) {
-    ToolChain.AddFortranStdlibLibArgs(Args, CmdArgs);
-  } else {
-    // Claim "no Flang libraries" arguments if any
-    for (auto Arg : Args.filtered(options::OPT_noFlangLibs)) {
-      Arg->claim();
-    }
-  }
-#endif
-
   if (D.CCCIsCXX() &&
       !Args.hasArg(options::OPT_nostdlib, options::OPT_nodefaultlibs,
                    options::OPT_r)) {

clang/test/Driver/flang/classic-flang.f95

@@ -41,3 +41,49 @@
 ! CHECK-ASM-SAME: "-o" "classic-flang.s"
 ! CHECK-ASM-SAME: "-x" "ir"
 ! CHECK-ASM-SAME: [[LLFILE]]
+
+! Check that the linker job is given the correct libraries and library paths.
+
+! RUN: %flang -target x86_64-linux-gnu -ccc-install-dir %S/../Inputs/basic_linux_tree/usr/bin -mp \
+! RUN:     %s -lfoo -### 2>&1 | FileCheck --check-prefixes=CHECK-LD,CHECK-DYNAMIC-FLANG,CHECK-DYNAMIC-OMP %s
+! RUN: %flang -target x86_64-linux-gnu -ccc-install-dir %S/../Inputs/basic_linux_tree/usr/bin -mp -nomp \
+! RUN:     %s -lfoo -### 2>&1 | FileCheck --check-prefixes=CHECK-LD,CHECK-DYNAMIC-FLANG,CHECK-NO-OMP %s
+! RUN: %flang -target x86_64-linux-gnu -ccc-install-dir %S/../Inputs/basic_linux_tree/usr/bin -fopenmp \
+! RUN:     %s -lfoo -### 2>&1 | FileCheck --check-prefixes=CHECK-LD,CHECK-DYNAMIC-FLANG,CHECK-DYNAMIC-OMP %s
+! RUN: %flang -target x86_64-linux-gnu -ccc-install-dir %S/../Inputs/basic_linux_tree/usr/bin -fopenmp -fno-openmp \
+! RUN:     %s -lfoo -### 2>&1 | FileCheck --check-prefixes=CHECK-LD,CHECK-DYNAMIC-FLANG,CHECK-NO-OMP %s
+! RUN: %flang -target x86_64-linux-gnu -ccc-install-dir %S/../Inputs/basic_linux_tree/usr/bin -fopenmp -static-openmp \
+! RUN:     %s -lfoo -### 2>&1 | FileCheck --check-prefixes=CHECK-LD,CHECK-DYNAMIC-FLANG,CHECK-STATIC-OMP %s
+! RUN: %flang -target x86_64-linux-gnu -ccc-install-dir %S/../Inputs/basic_linux_tree/usr/bin -fopenmp -static-flang-libs \
+! RUN:     %s -lfoo -### 2>&1 | FileCheck --check-prefixes=CHECK-LD,CHECK-STATIC-FLANG,CHECK-DYNAMIC-OMP %s
+! RUN: %flang -target x86_64-linux-gnu -ccc-install-dir %S/../Inputs/basic_linux_tree/usr/bin -static-flang-libs \
+! RUN:     %s -lfoo -### 2>&1 | FileCheck --check-prefixes=CHECK-LD,CHECK-STATIC-FLANG,CHECK-NO-OMP %s
+
+! CHECK-LD:                "{{.*}}ld"
+! CHECK-LD-NOT:            "-static"
+! CHECK-LD:                "{{[^"]*}}classic-flang-{{[^ ]*}}.o" "-lflangmain" "-lfoo" "-L{{[^ ]*}}/basic_linux_tree/usr/lib"
+! CHECK-DYNAMIC-FLANG-NOT: "-Bstatic"
+! CHECK-DYNAMIC-FLANG:     "-lflang" "-lflangrti" "-lpgmath" "-lpthread" "-lrt" "-lm"
+! CHECK-DYNAMIC-FLANG-NOT: "-Bdynamic"
+! CHECK-STATIC-FLANG:      "-Bstatic" "-lflang" "-lflangrti" "-lpgmath" "-Bdynamic" "-lpthread" "-lrt" "-lm"
+! CHECK-DYNAMIC-OMP-NOT:   "-Bstatic"
+! CHECK-DYNAMIC-OMP:       "-lomp" "-rpath" "{{[^ ]*}}/basic_linux_tree/usr/lib"
+! CHECK-DYNAMIC-OMP-NOT:   "-Bdynamic"
+! CHECK-STATIC-OMP:        "-Bstatic" "-lomp" "-Bdynamic" "-rpath" "{{[^ ]*}}/basic_linux_tree/usr/lib"
+! CHECK-NO-OMP-NOT:        "-lomp"
+
+! RUN: %flang -target x86_64-linux-gnu -ccc-install-dir %S/../Inputs/basic_linux_tree/usr/bin -static -static-flang-libs \
+! RUN:     %s -lfoo -### 2>&1 | FileCheck --check-prefixes=CHECK-LD-STATIC,CHECK-NO-OMP %s
+! RUN: %flang -target x86_64-linux-gnu -ccc-install-dir %S/../Inputs/basic_linux_tree/usr/bin -static -fopenmp \
+! RUN:     %s -lfoo -### 2>&1 | FileCheck --check-prefixes=CHECK-LD-STATIC,CHECK-STATIC-BOTH %s
+! RUN: %flang -target x86_64-linux-gnu -ccc-install-dir %S/../Inputs/basic_linux_tree/usr/bin -static -fopenmp -static-openmp \
+! RUN:     %s -lfoo -### 2>&1 | FileCheck --check-prefixes=CHECK-LD-STATIC,CHECK-STATIC-BOTH %s
+! CHECK-LD-STATIC:     "{{.*}}ld"
+! CHECK-LD-STATIC:     "-static" "-o" "a.out"
+! CHECK-LD-STATIC:     "{{[^"]*}}classic-flang-{{[^ ]*}}.o" "-lflangmain" "-lfoo" "-L{{[^ ]*}}/basic_linux_tree/usr/lib"
+! CHECK-LD-STATIC-NOT: "-Bstatic"
+! CHECK-LD-STATIC:     "-lflang" "-lflangrti" "-lpgmath" "-lpthread" "-lrt" "-lm"
+! CHECK-LD-STATIC-NOT: "-Bdynamic"
+! CHECK-STATIC-BOTH-NOT: "-Bstatic"
+! CHECK-STATIC-BOTH:     "-lomp"
+! CHECK-STATIC-BOTH-NOT: "-Bdynamic"