[flang][OpenMP] Add initial pass to map do concurrent to OMP

clang/include/clang/Driver/Options.td

@@ -6473,6 +6473,10 @@ 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 do_concurrent_parallel_EQ : Joined<["-"], "fdo-concurrent-parallel=">,
+  HelpText<"Try to map `do concurrent` loops to OpenMP (on host or device)">,
+      Values<"none,host,device">;
 } // let Visibility = [FC1Option, FlangOption]
 
 def J : JoinedOrSeparate<["-"], "J">,

clang/lib/Driver/ToolChains/Flang.cpp

@@ -150,7 +150,8 @@ void Flang::addCodegenOptions(const ArgList &Args,
                             options::OPT_flang_deprecated_no_hlfir,
                             options::OPT_flang_experimental_polymorphism,
                             options::OPT_fno_ppc_native_vec_elem_order,
-                            options::OPT_fppc_native_vec_elem_order});
+                            options::OPT_fppc_native_vec_elem_order,
+                            options::OPT_do_concurrent_parallel_EQ});
 }
 
 void Flang::addPicOptions(const ArgList &Args, ArgStringList &CmdArgs) const {

flang/include/flang/Frontend/CodeGenOptions.def

@@ -40,5 +40,7 @@ ENUM_CODEGENOPT(DebugInfo,  llvm::codegenoptions::DebugInfoKind, 4,  llvm::codeg
 ENUM_CODEGENOPT(VecLib, llvm::driver::VectorLibrary, 3, llvm::driver::VectorLibrary::NoLibrary) ///< Vector functions library to use
 ENUM_CODEGENOPT(FramePointer, llvm::FramePointerKind, 2, llvm::FramePointerKind::None) ///< Enable the usage of frame pointers
 
+ENUM_CODEGENOPT(DoConcurrentMapping, DoConcurrentMappingKind, 2, DoConcurrentMappingKind::DCMK_None) ///< Map `do concurrent` to OpenMP
+
 #undef CODEGENOPT
 #undef ENUM_CODEGENOPT

flang/include/flang/Frontend/CodeGenOptions.h

@@ -129,6 +129,14 @@ class CodeGenOptions : public CodeGenOptionsBase {
   /// transformation.
   OptRemark OptimizationRemarkAnalysis;
 
+  /// Optionally map `do concurrent` loops to OpenMP. This is only valid of
+  /// OpenMP is enabled.
+  enum class DoConcurrentMappingKind {
+    DCMK_None,  // Do not lower `do concurrent` to OpenMP.
+    DCMK_Host,  // Lower to run in parallel on the CPU.
+    DCMK_Device // Lower to run in parallel on the GPU.
+  };
+
   // Define accessors/mutators for code generation options of enumeration type.
 #define CODEGENOPT(Name, Bits, Default)
 #define ENUM_CODEGENOPT(Name, Type, Bits, Default)                             \

flang/include/flang/Optimizer/Transforms/Passes.h

@@ -96,6 +96,8 @@ createFunctionAttrPass(FunctionAttrTypes &functionAttr, bool noInfsFPMath,
                        bool noNaNsFPMath, bool approxFuncFPMath,
                        bool noSignedZerosFPMath, bool unsafeFPMath);
 
+std::unique_ptr<mlir::Pass> createDoConcurrentConversionPass();
+
 // declarative passes
 #define GEN_PASS_REGISTRATION
 #include "flang/Optimizer/Transforms/Passes.h.inc"

flang/include/flang/Optimizer/Transforms/Passes.td

@@ -397,4 +397,24 @@ def FunctionAttr : Pass<"function-attr", "mlir::func::FuncOp"> {
   let constructor = "::fir::createFunctionAttrPass()";
 }
 
+def DoConcurrentConversionPass : Pass<"fopenmp-do-concurrent-conversion", "mlir::func::FuncOp"> {
+  let summary = "Map `DO CONCURRENT` loops to OpenMP worksharing loops.";
+
+  let description = [{ This is an experimental pass to map `DO CONCURRENT` loops
+     to their correspnding equivalent OpenMP worksharing constructs.
+
+     For now the following is supported:
+       - Mapping simple loops to `parallel do`.
+
+     Still to TODO:
+       - More extensive testing.
+       - Mapping to `target teams distribute parallel do`.
+       - Allowing the user to control mapping behavior: either to the host or
+         target.
+  }];
+
+  let constructor = "::fir::createDoConcurrentConversionPass()";
+  let dependentDialects = ["mlir::omp::OpenMPDialect"];
+}
+
 #endif // FLANG_OPTIMIZER_TRANSFORMS_PASSES

flang/lib/Frontend/CompilerInvocation.cpp

@@ -154,6 +154,32 @@ static bool parseDebugArgs(Fortran::frontend::CodeGenOptions &opts,
   return true;
 }
 
+static bool parseDoConcurrentMapping(Fortran::frontend::CodeGenOptions &opts,
+                                     llvm::opt::ArgList &args,
+                                     clang::DiagnosticsEngine &diags) {
+  llvm::opt::Arg *arg =
+      args.getLastArg(clang::driver::options::OPT_do_concurrent_parallel_EQ);
+  if (!arg)
+    return true;
+
+  using DoConcurrentMappingKind = Fortran::frontend::CodeGenOptions::DoConcurrentMappingKind;
+  std::optional<DoConcurrentMappingKind> val =
+      llvm::StringSwitch<std::optional<DoConcurrentMappingKind>>(
+          arg->getValue())
+          .Case("none", DoConcurrentMappingKind::DCMK_None)
+          .Case("host", DoConcurrentMappingKind::DCMK_Host)
+          .Case("device", DoConcurrentMappingKind::DCMK_Device)
+          .Default(std::nullopt);
+
+  if (!val.has_value()) {
+    diags.Report(clang::diag::err_drv_invalid_value)
+        << arg->getAsString(args) << arg->getValue();
+    return false;
+  }
+  opts.setDoConcurrentMapping(val.value());
+  return true;
+}
+
 static bool parseVectorLibArg(Fortran::frontend::CodeGenOptions &opts,
                               llvm::opt::ArgList &args,
                               clang::DiagnosticsEngine &diags) {
@@ -385,6 +411,8 @@ static void parseCodeGenArgs(Fortran::frontend::CodeGenOptions &opts,
                    clang::driver::options::OPT_funderscoring, false)) {
     opts.Underscoring = 0;
   }
+
+  parseDoConcurrentMapping(opts, args, diags);
 }
 
 /// Parses all target input arguments and populates the target

flang/lib/Frontend/FrontendActions.cpp

@@ -320,8 +320,9 @@ bool CodeGenAction::beginSourceFileAction() {
   // Add OpenMP-related passes
   // WARNING: These passes must be run immediately after the lowering to ensure
   // that the FIR is correct with respect to OpenMP operations/attributes.
-  if (ci.getInvocation().getFrontendOpts().features.IsEnabled(
-          Fortran::common::LanguageFeature::OpenMP)) {
+  bool isOpenMPEnabled = ci.getInvocation().getFrontendOpts().features.IsEnabled(
+          Fortran::common::LanguageFeature::OpenMP);
+  if (isOpenMPEnabled) {
     bool isDevice = false;
     if (auto offloadMod = llvm::dyn_cast<mlir::omp::OffloadModuleInterface>(
             mlirModule->getOperation()))
@@ -332,6 +333,30 @@ bool CodeGenAction::beginSourceFileAction() {
     fir::createOpenMPFIRPassPipeline(pm, isDevice);
   }
 
+  using DoConcurrentMappingKind =
+      Fortran::frontend::CodeGenOptions::DoConcurrentMappingKind;
+  DoConcurrentMappingKind selectedKind = ci.getInvocation().getCodeGenOpts().getDoConcurrentMapping();
+  if (selectedKind != DoConcurrentMappingKind::DCMK_None) {
+    if (!isOpenMPEnabled) {
+      unsigned diagID = ci.getDiagnostics().getCustomDiagID(
+          clang::DiagnosticsEngine::Warning,
+          "lowering `do concurrent` loops to OpenMP is only supported if "
+          "OpenMP is enabled");
+      ci.getDiagnostics().Report(diagID);
+    } else {
+      bool mapToDevice = selectedKind == DoConcurrentMappingKind::DCMK_Device;
+
+      if (mapToDevice) {
+        unsigned diagID = ci.getDiagnostics().getCustomDiagID(
+            clang::DiagnosticsEngine::Warning,
+            "TODO: lowering `do concurrent` loops to OpenMP device is not "
+            "supported yet");
+        ci.getDiagnostics().Report(diagID);
+      } else
+        pm.addPass(fir::createDoConcurrentConversionPass());
+    }
+  }
+
   pm.enableVerifier(/*verifyPasses=*/true);
   pm.addPass(std::make_unique<Fortran::lower::VerifierPass>());
 

flang/lib/Optimizer/Transforms/CMakeLists.txt

@@ -22,6 +22,7 @@ add_flang_library(FIRTransforms
   OMPMarkDeclareTarget.cpp
   VScaleAttr.cpp
   FunctionAttr.cpp
+  DoConcurrentConversion.cpp
 
   DEPENDS
   FIRDialect