[Clang] Introduce '--offload-targets=' to genericall target toolchains

Summary:
This is a new option that tries to make selecting offloading toolchains
more generic. Currently we infer the toolchain from a combination of the
kind and the `--offload-arch=` option. Doing this becomes complicated
when we want to start supporting multiple targets for a single
toolchain, i.e. HIP on SPIR-V or AMDGCN. Currently we hack in a special
'architecture' instead, which isn't extensible. Additionally in the
future we may accept compiling CUDA or HIP to some other architecture.

Author: jhuber6

clang/include/clang/Basic/DiagnosticDriverKinds.td

@@ -116,6 +116,8 @@ def err_drv_cuda_host_arch : Error<
   "unsupported architecture '%0' for host compilation">;
 def err_drv_mix_cuda_hip : Error<
   "mixed CUDA and HIP compilation is not supported">;
+def err_drv_mix_offload : Error<
+  "mixed %0 and %1 offloading compilation is not supported">;
 def err_drv_bad_target_id : Error<
   "invalid target ID '%0'; format is a processor name followed by an optional "
   "colon-delimited list of features followed by an enable/disable sign (e.g., "

clang/include/clang/Driver/Driver.h

@@ -355,6 +355,9 @@ class Driver {
   phases::ID getFinalPhase(const llvm::opt::DerivedArgList &DAL,
                            llvm::opt::Arg **FinalPhaseArg = nullptr) const;
 
+  llvm::Expected<std::unique_ptr<llvm::MemoryBuffer>>
+  executeProgram(llvm::ArrayRef<llvm::StringRef> Args) const;
+
 private:
   /// Certain options suppress the 'no input files' warning.
   LLVM_PREFERRED_TYPE(bool)
@@ -367,6 +370,7 @@ class Driver {
   /// stored in it, and will clean them up when torn down.
   mutable llvm::StringMap<std::unique_ptr<ToolChain>> ToolChains;
 
+public:
   /// The associated offloading architectures with each toolchain.
   llvm::DenseMap<const ToolChain *, llvm::SmallVector<llvm::StringRef>>
       OffloadArchs;
@@ -537,8 +541,7 @@ class Driver {
   /// empty string.
   llvm::SmallVector<StringRef>
   getOffloadArchs(Compilation &C, const llvm::opt::DerivedArgList &Args,
-                  Action::OffloadKind Kind, const ToolChain *TC,
-                  bool SpecificToolchain = true) const;
+                  Action::OffloadKind Kind, const ToolChain &TC) const;
 
   /// Check that the file referenced by Value exists. If it doesn't,
   /// issue a diagnostic and return false.

clang/include/clang/Driver/Options.td

@@ -1156,7 +1156,7 @@ def offload_arch_EQ : CommaJoined<["--"], "offload-arch=">,
            "If 'native' is used the compiler will detect locally installed architectures. "
            "For HIP offloading, the device architecture can be followed by target ID features "
            "delimited by a colon (e.g. gfx908:xnack+:sramecc-). May be specified more than once.">;
-def no_offload_arch_EQ : Joined<["--"], "no-offload-arch=">,
+def no_offload_arch_EQ : CommaJoined<["--"], "no-offload-arch=">,
   Visibility<[ClangOption, FlangOption]>,
   HelpText<"Remove CUDA/HIP offloading device architecture (e.g. sm_35, gfx906) from the list of devices to compile for. "
            "'all' resets the list to its default value.">;
@@ -1637,7 +1637,7 @@ defm auto_import : BoolFOption<"auto-import",
 // In the future this option will be supported by other offloading
 // languages and accept other values such as CPU/GPU architectures,
 // offload kinds and target aliases.
-def offload_EQ : CommaJoined<["--"], "offload=">, Flags<[NoXarchOption]>,
+def offload_EQ : CommaJoined<["--"], "offload=">, Flags<[NoXarchOption]>, Alias<offload_targets_EQ>,
   HelpText<"Specify comma-separated list of offloading target triples (CUDA and HIP only)">;
 
 // C++ Coroutines

clang/include/clang/Driver/ToolChain.h

@@ -202,10 +202,6 @@ class ToolChain {
   ToolChain(const Driver &D, const llvm::Triple &T,
             const llvm::opt::ArgList &Args);
 
-  /// Executes the given \p Executable and returns the stdout.
-  llvm::Expected<std::unique_ptr<llvm::MemoryBuffer>>
-  executeToolChainProgram(StringRef Executable) const;
-
   void setTripleEnvironment(llvm::Triple::EnvironmentType Env);
 
   virtual Tool *buildAssembler() const;