[Clang][OpenMP] Fix behavior when -fopenmp is not present on command …

…line

When -fopenmp is not present, or gets hidden with -fno-openmp, compiler
shouldn't give up parsing the command line.

This will allow HPC users to pass -fno-openmp as override flag for
subset of their code which doesn't contain OpenMP code, without
writing new command lines by removing -fopenmp-targets, -Xopenmp-target,
-march, etc.

Fixes: SWDEV-294358 and SWDEV-323292

Change-Id: I82288adef2327fa590fd16d822acbf8cc9a1b541
(cherry picked from commit b266d5c)

clang/include/clang/Basic/DiagnosticDriverKinds.td

@@ -320,9 +320,9 @@ def err_drv_omp_host_ir_file_not_found : Error<
   "target regions but cannot be found">;
 def err_drv_omp_host_target_not_supported : Error<
   "target '%0' is not a supported OpenMP host target">;
-def err_drv_expecting_fopenmp_with_fopenmp_targets : Error<
+def warn_drv_expecting_fopenmp_with_fopenmp_targets : Warning<
   "'-fopenmp-targets' must be used in conjunction with a '-fopenmp' option "
-  "compatible with offloading; e.g., '-fopenmp=libomp' or '-fopenmp=libiomp5'">;
+  "compatible with offloading; e.g., '-fopenmp=libomp' or '-fopenmp=libiomp5'">, InGroup<OpenMPTarget>;
 def err_drv_omp_offload_target_missingbcruntime : Error<
   "no library '%0' found in the default clang lib directory or in LIBRARY_PATH"
   "; use '--libomptarget-%1-bc-path' to specify %1 bitcode library">;

clang/lib/Driver/Driver.cpp

@@ -875,6 +875,34 @@ void Driver::CreateOffloadingDeviceToolChains(Compilation &C,
     // may now contain targetid value. This value
     // may include features that would result in different and potentially
     // multiple offload images.
+
+    bool HasValidOpenMPRuntime =
+        C.getInputArgs().hasFlag(options::OPT_fopenmp, options::OPT_fopenmp_EQ,
+                                 options::OPT_fno_openmp, false);
+    if (HasValidOpenMPRuntime) {
+      OpenMPRuntimeKind OpenMPKind = getOpenMPRuntime(C.getInputArgs());
+      HasValidOpenMPRuntime =
+          OpenMPKind == OMPRT_OMP || OpenMPKind == OMPRT_IOMP5;
+    }
+
+    bool HasOpenMPTargets =
+        C.getInputArgs().hasArg(options::OPT_fopenmp_targets_EQ);
+    if (!HasValidOpenMPRuntime && HasOpenMPTargets) {
+      // We expect that an offload target is always used in conjunction with
+      // option -fopenmp specifying a valid runtime with offloading support,
+      // i.e. libomp or libiomp.
+      Diag(clang::diag::warn_drv_expecting_fopenmp_with_fopenmp_targets);
+      return;
+    } else if (!HasValidOpenMPRuntime && !HasOpenMPTargets) {
+      return;
+    }
+
+    bool HasOffloadArch = C.getInputArgs().hasFlag(
+        options::OPT_offload_arch_EQ, options::OPT_no_offload_arch_EQ, false);
+    if (HasValidOpenMPRuntime && !HasOpenMPTargets && !HasOffloadArch) {
+      return;
+    }
+
     std::set<std::string> OffloadArchs;
 
     if (Arg *OpenMPTargets =
@@ -950,22 +978,6 @@ void Driver::CreateOffloadingDeviceToolChains(Compilation &C,
         }
       }
 
-      // We expect that an offload target is always used in conjunction with
-      // option -fopenmp specifying a valid runtime with offloading support,
-      // i.e. libomp or libiomp.
-      bool HasValidOpenMPRuntime = C.getInputArgs().hasFlag(
-          options::OPT_fopenmp, options::OPT_fopenmp_EQ,
-          options::OPT_fno_openmp, false);
-      if (HasValidOpenMPRuntime) {
-        OpenMPRuntimeKind OpenMPKind = getOpenMPRuntime(C.getInputArgs());
-        HasValidOpenMPRuntime =
-            OpenMPKind == OMPRT_OMP || OpenMPKind == OMPRT_IOMP5;
-      }
-      if (!HasValidOpenMPRuntime) {
-        Diag(clang::diag::err_drv_expecting_fopenmp_with_fopenmp_targets);
-        return;
-      }
-
       llvm::StringMap<const char *> FoundNormalizedTriples;
       for (auto &Target : OffloadArchs) {
         size_t find_loc = Target.find('^');

clang/test/Driver/openmp-offload-fnoopenmp.c

@@ -0,0 +1,40 @@
+// REQUIRES: clang-driver
+// REQUIRES: x86-registered-target
+// REQUIRES: amdgpu-registered-target
+
+// RUN: %clang -### -target x86_64-linux-gnu \
+// RUN:   --offload-arch=gfx906 \
+// RUN:   %s 2>&1 | FileCheck -check-prefix=OFFLOAD %s
+// OFFLOAD: warning: argument unused during compilation: '--offload-arch=gfx906'
+
+// RUN: %clang -### -target x86_64-linux-gnu -fopenmp\
+// RUN:   --offload-arch=gfx906 \
+// RUN:   -fno-openmp \
+// RUN:   %s 2>&1 | FileCheck -check-prefix=OFFLOAD1 %s
+// OFFLOAD1: warning: argument unused during compilation: '--offload-arch=gfx906'
+
+// RUN: %clang -### -target x86_64-linux-gnu -fopenmp\
+// RUN:   -fopenmp-targets=amdgcn-amd-amdhsa,amdgcn-amd-amdhsa \
+// RUN:   -Xopenmp-target=amdgcn-amd-amdhsa -march=gfx906 \
+// RUN:   -fno-openmp \
+// RUN:   %s 2>&1 | FileCheck -check-prefix=LEGACY %s
+// LEGACY: warning: '-fopenmp-targets' must be used in conjunction with a '-fopenmp' option compatible with offloading; e.g., '-fopenmp=libomp' or '-fopenmp=libiomp5'
+// LEGACY-NEXT: warning: argument unused during compilation: '-Xopenmp-target=amdgcn-amd-amdhsa -march=gfx906'
+
+// RUN: %clang -### -target x86_64-linux-gnu -fopenmp\
+// RUN:   --offload-arch=gfx906 \
+// RUN:   --offload-arch=gfx908 \
+// RUN:   -fno-openmp \
+// RUN:   %s 2>&1 | FileCheck -check-prefix=MOFFLOAD %s
+// MOFFLOAD: warning: argument unused during compilation: '--offload-arch=gfx906'
+// MOFFLOAD-NEXT: warning: argument unused during compilation: '--offload-arch=gfx908'
+
+// RUN: %clang -### -target x86_64-linux-gnu -fopenmp\
+// RUN:   -fopenmp-targets=amdgcn-amd-amdhsa,amdgcn-amd-amdhsa \
+// RUN:   -Xopenmp-target=amdgcn-amd-amdhsa -march=gfx906 \
+// RUN:   -Xopenmp-target=amdgcn-amd-amdhsa -march=gfx908 \
+// RUN:   -fno-openmp \
+// RUN:   %s 2>&1 | FileCheck -check-prefix=MLEGACY %s
+// MLEGACY: warning: '-fopenmp-targets' must be used in conjunction with a '-fopenmp' option compatible with offloading; e.g., '-fopenmp=libomp' or '-fopenmp=libiomp5'
+// MLEGACY: warning: argument unused during compilation: '-Xopenmp-target=amdgcn-amd-amdhsa -march=gfx906'
+// MLEGACY: warning: argument unused during compilation: '-Xopenmp-target=amdgcn-amd-amdhsa -march=gfx908'