[flang][Driver] Support -print-supported-cpus and associated aliases

The aliases are -mcpu=help and -mtune=help. There is still an issue with the
output which prints an example line that references clang. That is not fixed
here because it is printed in llvm/MC/SubtargetInfo.cpp. Some more thought is
needed to determine how best to handle this.

Fixes #117010

Author: Tarun Prabhu

clang/include/clang/Driver/Options.td

@@ -5890,7 +5890,7 @@ def darwin_target_variant : Separate<["-"], "darwin-target-variant">,
   HelpText<"Generate code for an additional runtime variant of the deployment target">;
 def print_supported_cpus : Flag<["-", "--"], "print-supported-cpus">,
   Group<CompileOnly_Group>,
-  Visibility<[ClangOption, CC1Option, CLOption]>,
+  Visibility<[ClangOption, CC1Option, CLOption, FlangOption, FC1Option]>,
   HelpText<"Print supported cpu models for the given target (if target is not specified,"
            " it will print the supported cpus for the default target)">,
   MarshallingInfoFlag<FrontendOpts<"PrintSupportedCPUs">>;
@@ -5903,8 +5903,10 @@ def print_enabled_extensions : Flag<["-", "--"], "print-enabled-extensions">,
   HelpText<"Print the extensions enabled by the given target and -march/-mcpu options."
            " (AArch64 and RISC-V only)">,
   MarshallingInfoFlag<FrontendOpts<"PrintEnabledExtensions">>;
-def : Flag<["-"], "mcpu=help">, Alias<print_supported_cpus>;
-def : Flag<["-"], "mtune=help">, Alias<print_supported_cpus>;
+def : Flag<["-"], "mcpu=help">, Alias<print_supported_cpus>,
+  Visibility<[ClangOption, CC1Option, CLOption, FlangOption, FC1Option]>;
+def : Flag<["-"], "mtune=help">, Alias<print_supported_cpus>,
+  Visibility<[ClangOption, CC1Option, CLOption, FlangOption, FC1Option]>;
 def time : Flag<["-"], "time">,
   HelpText<"Time individual commands">;
 def traditional_cpp : Flag<["-", "--"], "traditional-cpp">,

clang/lib/Driver/Driver.cpp

@@ -4417,7 +4417,8 @@ void Driver::BuildActions(Compilation &C, DerivedArgList &Args,
 
       // Use the -mcpu=? flag as the dummy input to cc1.
       Actions.clear();
-      Action *InputAc = C.MakeAction<InputAction>(*A, types::TY_C);
+      Action *InputAc = C.MakeAction<InputAction>(
+          *A, IsFlangMode() ? types::TY_Fortran : types::TY_C);
       Actions.push_back(
           C.MakeAction<PrecompileJobAction>(InputAc, types::TY_Nothing));
       for (auto &I : Inputs)
@@ -6621,8 +6622,8 @@ bool Driver::ShouldUseFlangCompiler(const JobAction &JA) const {
     return false;
 
   // And say "no" if this is not a kind of action flang understands.
-  if (!isa<PreprocessJobAction>(JA) && !isa<CompileJobAction>(JA) &&
-      !isa<BackendJobAction>(JA))
+  if (!isa<PreprocessJobAction>(JA) && !isa<PrecompileJobAction>(JA) &&
+      !isa<CompileJobAction>(JA) && !isa<BackendJobAction>(JA))
     return false;
 
   return true;

clang/lib/Driver/ToolChains/Flang.cpp

@@ -747,6 +747,9 @@ void Flang::ConstructJob(Compilation &C, const JobAction &JA,
     }
   } else if (isa<AssembleJobAction>(JA)) {
     CmdArgs.push_back("-emit-obj");
+  } else if (isa<PrecompileJobAction>(JA)) {
+    // The Precompile job action is only needed for options such as -mcpu=help.
+    // Those will already have been handled by the fc1 driver.
   } else {
     assert(false && "Unexpected action class for Flang tool.");
   }
@@ -911,8 +914,6 @@ void Flang::ConstructJob(Compilation &C, const JobAction &JA,
     CmdArgs.push_back(Output.getFilename());
   }
 
-  assert(Input.isFilename() && "Invalid input.");
-
   if (Args.getLastArg(options::OPT_save_temps_EQ))
     Args.AddLastArg(CmdArgs, options::OPT_save_temps_EQ);
 
@@ -932,7 +933,18 @@ void Flang::ConstructJob(Compilation &C, const JobAction &JA,
     }
   }
 
-  CmdArgs.push_back(Input.getFilename());
+  // The input could be Ty_Nothing when "querying" options such as -mcpu=help
+  // are used.
+  ArrayRef<InputInfo> FrontendInputs = Input;
+  if (Input.isNothing())
+    FrontendInputs = {};
+
+  for (const InputInfo &Input : FrontendInputs) {
+    if (Input.isFilename())
+      CmdArgs.push_back(Input.getFilename());
+    else
+      Input.getInputArg().renderAsInput(Args, CmdArgs);
+  }
 
   const char *Exec = Args.MakeArgString(D.GetProgramPath("flang", TC));
   C.addCommand(std::make_unique<Command>(JA, *this,

flang/include/flang/Frontend/FrontendOptions.h

@@ -236,7 +236,8 @@ class FrontendInputFile {
 struct FrontendOptions {
   FrontendOptions()
       : showHelp(false), showVersion(false), instrumentedParse(false),
-        showColors(false), needProvenanceRangeToCharBlockMappings(false) {}
+        showColors(false), printSupportedCPUs(false),
+        needProvenanceRangeToCharBlockMappings(false) {}
 
   /// Show the -help text.
   unsigned showHelp : 1;
@@ -250,6 +251,9 @@ struct FrontendOptions {
   /// Enable color diagnostics.
   unsigned showColors : 1;
 
+  /// print the supported cpus for the current target
+  unsigned printSupportedCPUs : 1;
+
   /// Enable Provenance to character-stream mapping. Allows e.g. IDEs to find
   /// symbols based on source-code location. This is not needed in regular
   /// compilation.

flang/lib/Frontend/CompilerInvocation.cpp

@@ -634,6 +634,8 @@ static bool parseFrontendArgs(FrontendOptions &opts, llvm::opt::ArgList &args,
   opts.outputFile = args.getLastArgValue(clang::driver::options::OPT_o);
   opts.showHelp = args.hasArg(clang::driver::options::OPT_help);
   opts.showVersion = args.hasArg(clang::driver::options::OPT_version);
+  opts.printSupportedCPUs =
+      args.hasArg(clang::driver::options::OPT_print_supported_cpus);
 
   // Get the input kind (from the value passed via `-x`)
   InputKind dashX(Language::Unknown);

flang/test/Driver/print-supported-cpus-aarch64.f90

@@ -0,0 +1,23 @@
+! Test --print-supported-cpus and associated aliases, -mcpu=help and
+! -mtune=help on AArch64.
+
+! REQUIRES: aarch64-registered-target
+
+! RUN: %flang --target=aarch64-unknown-linux-gnu --print-supported-cpus 2>&1 | \
+! RUN:   FileCheck %s
+! RUN: %flang --target=aarch64-unknown-linux-gnu -mcpu=help 2>&1 | \
+! RUN:   FileCheck %s
+! RUN: %flang --target=aarch64-unknown-linux-gnu -mtune=help 2>&1 | \
+! RUN:   FileCheck %s
+
+! CHECK-NOT: warning: argument unused during compilation
+
+! CHECK: Target: aarch64-unknown-linux-gnu
+! CHECK: cortex-a73
+! CHECK: cortex-a75
+
+! TODO: This is a line that is printed at the end of the output. The full line
+! also includes an example that references clang. That needs to be fixed and a
+! a check added here to make sure that it references flang, not clang.
+
+! CHECK: Use -mcpu or -mtune to specify the target's processor.

flang/test/Driver/print-supported-cpus-x86.f90

@@ -0,0 +1,22 @@
+! Test --print-supported-cpus and associated aliases, -mcpu=help and
+! -mtune=help on X86.
+
+! REQUIRES: x86-registered-target
+
+! RUN: %flang --target=x86_64-unknown-linux-gnu --print-supported-cpus 2>&1 | \
+! RUN:   FileCheck %s
+! RUN: %flang --target=x86_64-unknown-linux-gnu -mcpu=help 2>&1 | \
+! RUN:   FileCheck %s
+! RUN: %flang --target=x86_64-unknown-linux-gnu -mtune=help 2>&1 | \
+! RUN:   FileCheck %s
+
+! CHECK-NOT: warning: argument unused during compilation
+
+! CHECK: Target: x86_64-unknown-linux-gnu
+! CHECK: corei7
+
+! TODO: This is a line that is printed at the end of the output. The full line
+! also includes an example that references clang. That needs to be fixed and a
+! a check added here to make sure that it references flang, not clang.
+
+! CHECK: Use -mcpu or -mtune to specify the target's processor.

flang/tools/flang-driver/fc1_main.cpp

@@ -21,15 +21,35 @@
 #include "flang/Frontend/TextDiagnosticBuffer.h"
 #include "flang/FrontendTool/Utils.h"
 #include "clang/Driver/DriverDiagnostic.h"
+#include "llvm/MC/TargetRegistry.h"
 #include "llvm/Option/Arg.h"
 #include "llvm/Option/ArgList.h"
 #include "llvm/Option/OptTable.h"
 #include "llvm/Support/TargetSelect.h"
+#include "llvm/Support/raw_ostream.h"
 
 #include <cstdio>
 
 using namespace Fortran::frontend;
 
+/// Print supported cpus of the given target.
+static int printSupportedCPUs(llvm::StringRef triple) {
+  std::string error;
+  const llvm::Target *target =
+      llvm::TargetRegistry::lookupTarget(triple, error);
+  if (!target) {
+    llvm::errs() << error;
+    return 1;
+  }
+
+  // the target machine will handle the mcpu printing
+  llvm::TargetOptions targetOpts;
+  std::unique_ptr<llvm::TargetMachine> targetMachine(
+      target->createTargetMachine(triple, "", "+cpuhelp", targetOpts,
+                                  std::nullopt));
+  return 0;
+}
+
 int fc1_main(llvm::ArrayRef<const char *> argv, const char *argv0) {
   // Create CompilerInstance
   std::unique_ptr<CompilerInstance> flang(new CompilerInstance());
@@ -58,6 +78,10 @@ int fc1_main(llvm::ArrayRef<const char *> argv, const char *argv0) {
   llvm::InitializeAllTargetMCs();
   llvm::InitializeAllAsmPrinters();
 
+  // --print-supported-cpus takes priority over the actual compilation.
+  if (flang->getFrontendOpts().printSupportedCPUs)
+    return printSupportedCPUs(flang->getInvocation().getTargetOpts().triple);
+
   diagsBuffer->flushDiagnostics(flang->getDiagnostics());
 
   if (!success)