[Flang][Driver] Introduce -fopenmp-targets offloading option

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

@@ -3530,7 +3530,7 @@ 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/Flang.cpp

@@ -12,6 +12,7 @@
 
 #include "clang/Basic/CodeGenOptions.h"
 #include "clang/Driver/Options.h"
+#include "llvm/ADT/StringExtras.h"
 #include "llvm/Frontend/Debug/Options.h"
 #include "llvm/Support/FileSystem.h"
 #include "llvm/Support/Path.h"
@@ -492,6 +493,18 @@ void Flang::addOffloadOptions(Compilation &C, const InputInfoList &Inputs,
     if (Args.hasArg(options::OPT_nogpulib))
       CmdArgs.push_back("-nogpulib");
   }
+
+  // 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, ",")));
+  }
 }
 
 static void addFloatingPointOptions(const Driver &D, const ArgList &Args,

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

@@ -227,3 +227,20 @@
 ! FORCE-USM-OFFLOAD-SAME: "-fopenmp" "-fopenmp-force-usm"
 ! FORCE-USM-OFFLOAD-NEXT: "{{[^"]*}}flang-new" "-fc1" "-triple" "amdgcn-amd-amdhsa"
 ! FORCE-USM-OFFLOAD-SAME: "-fopenmp" "-fopenmp-force-usm"
+
+! RUN: %flang -S -### %s -o %t 2>&1 \
+! RUN: -fopenmp -fopenmp-targets=amdgcn-amd-amdhsa \
+! RUN: --target=aarch64-unknown-linux-gnu \
+! RUN: | FileCheck %s --check-prefix=OFFLOAD-TARGETS
+
+! RUN: %flang -S -### %s -o %t 2>&1 \
+! RUN: -fopenmp --offload-arch=gfx90a \
+! RUN: --target=aarch64-unknown-linux-gnu \
+! RUN: | FileCheck %s --check-prefix=OFFLOAD-TARGETS
+
+! OFFLOAD-TARGETS: "{{[^"]*}}flang-new" "-fc1" "-triple" "aarch64-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" "aarch64-unknown-linux-gnu"
+! OFFLOAD-TARGETS-SAME: "-fopenmp-targets=amdgcn-amd-amdhsa"