[OpenMP] Don't build the offloading driver without a source input

The Clang driver additional stages to build a complete offloading
program for applications using CUDA or OpenMP offloading. This normally
requires either a source file input or a valid object file to be
handled. This would cause problems when trying to compile an assembly or
LLVM IR file through clang with flags that would enable offloading. This
patch simply adds a check to prevent the offloading toolchain from being
used if we don't have a valid source file.

Reviewed By: jdoerfert

Differential Revision: https://reviews.llvm.org/D125705

clang/lib/Driver/Driver.cpp

@@ -4377,9 +4377,11 @@ Action *Driver::BuildOffloadingActions(Compilation &C,
       Mode && Mode->getOption().matches(options::OPT_offload_device_only);
 
   // Don't build offloading actions if explicitly disabled or we do not have a
-  // compile action to embed it in. If preprocessing only ignore embedding.
-  if (HostOnly || !(isa<CompileJobAction>(HostAction) ||
-                    getFinalPhase(Args) == phases::Preprocess))
+  // valid source input and compile action to embed it in. If preprocessing only
+  // ignore embedding.
+  if (HostOnly || !types::isSrcFile(Input.first) ||
+      !(isa<CompileJobAction>(HostAction) ||
+        getFinalPhase(Args) == phases::Preprocess))
     return HostAction;
 
   ActionList OffloadActions;

clang/test/Driver/openmp-offload-gpu-new.c

@@ -70,6 +70,11 @@
 // CHECK-NVIDIA-AMDGPU: "x86_64-unknown-linux-gnu" - "clang", inputs: ["[[HOST_BC]]", "[[BINARY]]"], output: "[[HOST_OBJ:.+]]"
 // CHECK-NVIDIA-AMDGPU: "x86_64-unknown-linux-gnu" - "Offload::Linker", inputs: ["[[HOST_OBJ]]"], output: "a.out"
 
+// RUN:   %clang -x ir -### --target=x86_64-unknown-linux-gnu -ccc-print-bindings -fopenmp --offload-arch=sm_52 -nogpulib %s 2>&1 | FileCheck %s --check-prefix=CHECK-IR
+
+// CHECK-IR: "x86_64-unknown-linux-gnu" - "clang", inputs: ["[[INPUT_IR:.+]]"], output: "[[OBJECT:.+]]"
+// CHECK-IR: "x86_64-unknown-linux-gnu" - "Offload::Linker", inputs: ["[[OBJECT]]"], output: "a.out"
+
 // RUN:   %clang -### --target=x86_64-unknown-linux-gnu -emit-llvm -S -fopenmp -fopenmp-targets=nvptx64-nvidia-cuda -Xopenmp-target=nvptx64-nvidia-cuda -march=sm_52 -nogpulib %s 2>&1 | FileCheck %s --check-prefix=CHECK-EMIT-LLVM-IR
 // CHECK-EMIT-LLVM-IR: "-cc1"{{.*}}"-triple" "nvptx64-nvidia-cuda"{{.*}}"-emit-llvm"