[Flang][Driver] Introduce -fopenmp-targets offloading option (llvm#100152)

This patch modifies the flang driver to introduce the `-fopenmp-targets`
option to the frontend compiler invocations corresponding to the OpenMP
host device on offloading-enabled compilations.

This option holds the list of offloading triples associated to the
compilation and is used by clang to determine whether offloading calls
should be generated for the host.

Author: skatrak

clang/include/clang/Driver/Options.td

@@ -3532,7 +3532,7 @@ def fopenmp_use_tls : Flag<["-"], "fopenmp-use-tls">, Group<f_Group>,
 def fnoopenmp_use_tls : Flag<["-"], "fnoopenmp-use-tls">, Group<f_Group>,
   Flags<[NoArgumentUnused, HelpHidden]>, Visibility<[ClangOption, CC1Option]>;
 def fopenmp_targets_EQ : CommaJoined<["-"], "fopenmp-targets=">,
-  Flags<[NoXarchOption]>, Visibility<[ClangOption, CC1Option, FlangOption]>,
+  Flags<[NoXarchOption]>, Visibility<[ClangOption, CC1Option, FlangOption, FC1Option]>,
   HelpText<"Specify comma-separated list of triples OpenMP offloading targets to be supported">;
 def fopenmp_relocatable_target : Flag<["-"], "fopenmp-relocatable-target">,
   Group<f_Group>, Flags<[NoArgumentUnused, HelpHidden]>,

clang/lib/Driver/ToolChains/Clang.cpp

@@ -7789,17 +7789,7 @@ void Clang::ConstructJob(Compilation &C, const JobAction &JA,
                        options::OPT_mno_amdgpu_ieee);
   }
 
-  // For all the host OpenMP offloading compile jobs we need to pass the targets
-  // information using -fopenmp-targets= option.
-  if (JA.isHostOffloading(Action::OFK_OpenMP)) {
-    SmallString<128> Targets("-fopenmp-targets=");
-
-    SmallVector<std::string, 4> Triples;
-    auto TCRange = C.getOffloadToolChains<Action::OFK_OpenMP>();
-    std::transform(TCRange.first, TCRange.second, std::back_inserter(Triples),
-                   [](auto TC) { return TC.second->getTripleString(); });
-    CmdArgs.push_back(Args.MakeArgString(Targets + llvm::join(Triples, ",")));
-  }
+  addOpenMPHostOffloadingArgs(C, JA, Args, CmdArgs);
 
   bool VirtualFunctionElimination =
       Args.hasFlag(options::OPT_fvirtual_function_elimination,

clang/lib/Driver/ToolChains/CommonArgs.cpp

@@ -1244,6 +1244,25 @@ bool tools::addOpenMPRuntime(const Compilation &C, ArgStringList &CmdArgs,
   return true;
 }
 
+void tools::addOpenMPHostOffloadingArgs(const Compilation &C,
+                                        const JobAction &JA,
+                                        const llvm::opt::ArgList &Args,
+                                        llvm::opt::ArgStringList &CmdArgs) {
+  if (!JA.isHostOffloading(Action::OFK_OpenMP))
+    return;
+
+  // For all the host OpenMP offloading compile jobs we need to pass the targets
+  // information using -fopenmp-targets= option.
+  constexpr llvm::StringLiteral Targets("-fopenmp-targets=");
+
+  SmallVector<std::string> Triples;
+  auto TCRange = C.getOffloadToolChains<Action::OFK_OpenMP>();
+  std::transform(TCRange.first, TCRange.second, std::back_inserter(Triples),
+                 [](auto TC) { return TC.second->getTripleString(); });
+  CmdArgs.push_back(
+      Args.MakeArgString(Twine(Targets) + llvm::join(Triples, ",")));
+}
+
 /// Add Fortran runtime libs
 void tools::addFortranRuntimeLibs(const ToolChain &TC, const ArgList &Args,
                                   llvm::opt::ArgStringList &CmdArgs) {

clang/lib/Driver/ToolChains/CommonArgs.h

@@ -119,6 +119,11 @@ bool addOpenMPRuntime(const Compilation &C, llvm::opt::ArgStringList &CmdArgs,
                       bool ForceStaticHostRuntime = false,
                       bool IsOffloadingHost = false, bool GompNeedsRT = false);
 
+/// Adds offloading options for OpenMP host compilation to \p CmdArgs.
+void addOpenMPHostOffloadingArgs(const Compilation &C, const JobAction &JA,
+                                 const llvm::opt::ArgList &Args,
+                                 llvm::opt::ArgStringList &CmdArgs);
+
 /// Adds Fortran runtime libraries to \p CmdArgs.
 void addFortranRuntimeLibs(const ToolChain &TC, const llvm::opt::ArgList &Args,
                            llvm::opt::ArgStringList &CmdArgs);

clang/lib/Driver/ToolChains/Flang.cpp

@@ -495,6 +495,8 @@ void Flang::addOffloadOptions(Compilation &C, const InputInfoList &Inputs,
     if (Args.hasArg(options::OPT_nogpulib))
       CmdArgs.push_back("-nogpulib");
   }
+
+  addOpenMPHostOffloadingArgs(C, JA, Args, CmdArgs);
 }
 
 static void addFloatingPointOptions(const Driver &D, const ArgList &Args,

flang/test/Driver/omp-driver-offload.f90

@@ -207,3 +207,21 @@
 ! RUN:   | FileCheck --check-prefix=MLINK-BUILTIN-BITCODE  %s
 ! MLINK-BUILTIN-BITCODE:      "{{[^"]*}}flang-new" "-fc1" "-triple" "amdgcn-amd-amdhsa"
 ! MLINK-BUILTIN-BITCODE-SAME: "-mlink-builtin-bitcode" {{.*Inputs.*rocm.*amdgcn.*bitcode.*}}oclc_isa_version_900.bc
+
+! Test that the -fopenmp-targets option is added to host compilation invocations
+! when --offload-arch or -fopenmp-targets are set.
+! RUN: %flang -S -### %s -o %t 2>&1 \
+! RUN: -fopenmp --offload-arch=gfx90a \
+! RUN: --target=x86_64-unknown-linux-gnu -nogpulib \
+! RUN: | FileCheck %s --check-prefix=OFFLOAD-TARGETS
+! RUN: %flang -S -### %s -o %t 2>&1 \
+! RUN: -fopenmp -fopenmp-targets=amdgcn-amd-amdhsa --offload-arch=gfx90a \
+! RUN: --target=x86_64-unknown-linux-gnu -nogpulib \
+! RUN: | FileCheck %s --check-prefix=OFFLOAD-TARGETS
+
+! OFFLOAD-TARGETS: "{{[^"]*}}flang-new" "-fc1" "-triple" "x86_64-unknown-linux-gnu"
+! OFFLOAD-TARGETS-SAME: "-fopenmp-targets=amdgcn-amd-amdhsa"
+! OFFLOAD-TARGETS-NEXT: "{{[^"]*}}flang-new" "-fc1" "-triple" "amdgcn-amd-amdhsa"
+! OFFLOAD-TARGETS-NOT: -fopenmp-targets
+! OFFLOAD-TARGETS: "{{[^"]*}}flang-new" "-fc1" "-triple" "x86_64-unknown-linux-gnu"
+! OFFLOAD-TARGETS-SAME: "-fopenmp-targets=amdgcn-amd-amdhsa"