[clang] Add the ability to link libclc OpenCL libraries (llvm#146503)

This commit adds driver support for linking libclc OpenCL libraries. It
takes the form of a new optional flag: --libclc-lib=namespec. Nothing is
linked unless this flag is specified.

Not all libclc targets have corresponding clang targets. For this reason
it is desirable for users to be able to specify a libclc library name.
We support this by taking both a library name (without the .bc suffix)
or a filename. Both of these are searched for in the clang resource
directory. Filenames are
also checked themselves so that absolute paths can be provided. The
syntax for specifying filenames (as opposed to library names) uses a
leading colon (:), inspired by the -l option.

To accommodate this option, libclc libraries are now placed into clang's
resource directory in an in-tree configuration. The libraries are all
placed in <resource-dir>/lib/libclc and
are not grouped under host-specific directories as some other runtime
libraries are; it is not expected that OpenCL libraries will differ
depending on the host toolchain.

Currently only the AMDGPU toolchain supports this option as a proof of
concept. Other targets such as NVPTX or SPIR/SPIR-V could support it
too. We could optionally let target toolchains search for libclc
libraries themselves, possibly when passed an empty --libclc-lib.

Author: frasercrmck

clang/include/clang/Basic/DiagnosticDriverKinds.td

@@ -394,6 +394,8 @@ def warn_drv_fraw_string_literals_in_cxx11 : Warning<
   "ignoring '-f%select{no-|}0raw-string-literals', which is only valid for C and C++ standards before C++11">,
   InGroup<UnusedCommandLineArgument>;
 
+def err_drv_libclc_not_found : Error<"no libclc library '%0' found in the clang resource directory">;
+
 def err_drv_invalid_malign_branch_EQ : Error<
   "invalid argument '%0' to -malign-branch=; each element must be one of: %1">;
 

clang/include/clang/Driver/CommonArgs.h

@@ -215,6 +215,9 @@ void addOpenMPDeviceRTL(const Driver &D, const llvm::opt::ArgList &DriverArgs,
                         StringRef BitcodeSuffix, const llvm::Triple &Triple,
                         const ToolChain &HostTC);
 
+void addOpenCLBuiltinsLib(const Driver &D, const llvm::opt::ArgList &DriverArgs,
+                          llvm::opt::ArgStringList &CC1Args);
+
 void addOutlineAtomicsArgs(const Driver &D, const ToolChain &TC,
                            const llvm::opt::ArgList &Args,
                            llvm::opt::ArgStringList &CmdArgs,

clang/include/clang/Driver/Options.td

@@ -1422,6 +1422,21 @@ def fno_hip_emit_relocatable : Flag<["-"], "fno-hip-emit-relocatable">,
   HelpText<"Do not override toolchain to compile HIP source to relocatable">;
 }
 
+// Clang specific/exclusive options for OpenACC.
+def openacc_macro_override
+    : Separate<["-"], "fexperimental-openacc-macro-override">,
+      Visibility<[ClangOption, CC1Option]>,
+      Group<f_Group>,
+      HelpText<"Overrides the _OPENACC macro value for experimental testing "
+               "during OpenACC support development">;
+def openacc_macro_override_EQ
+    : Joined<["-"], "fexperimental-openacc-macro-override=">,
+      Alias<openacc_macro_override>;
+
+// End Clang specific/exclusive options for OpenACC.
+
+def libclc_lib_EQ : Joined<["--"], "libclc-lib=">, Group<opencl_Group>,
+  HelpText<"Namespec of libclc OpenCL bitcode library to link">;
 def libomptarget_amdgpu_bc_path_EQ : Joined<["--"], "libomptarget-amdgpu-bc-path=">, Group<i_Group>,
   HelpText<"Path to libomptarget-amdgcn bitcode library">;
 def libomptarget_amdgcn_bc_path_EQ : Joined<["--"], "libomptarget-amdgcn-bc-path=">, Group<i_Group>,

clang/lib/Driver/ToolChains/AMDGPU.cpp

@@ -857,6 +857,9 @@ void AMDGPUToolChain::addClangTargetOptions(
     CC1Args.push_back("-fvisibility=hidden");
     CC1Args.push_back("-fapply-global-visibility-to-externs");
   }
+
+  if (DeviceOffloadingKind == Action::OFK_None)
+    addOpenCLBuiltinsLib(getDriver(), DriverArgs, CC1Args);
 }
 
 void AMDGPUToolChain::addClangWarningOptions(ArgStringList &CC1Args) const {

clang/lib/Driver/ToolChains/CommonArgs.cpp

@@ -2985,6 +2985,43 @@ void tools::addHIPRuntimeLibArgs(const ToolChain &TC, Compilation &C,
   }
 }
 
+void tools::addOpenCLBuiltinsLib(const Driver &D,
+                                 const llvm::opt::ArgList &DriverArgs,
+                                 llvm::opt::ArgStringList &CC1Args) {
+  // Check whether user specifies a libclc bytecode library
+  const Arg *A = DriverArgs.getLastArg(options::OPT_libclc_lib_EQ);
+  if (!A)
+    return;
+
+  // Find device libraries in <LLVM_DIR>/lib/clang/<ver>/lib/libclc/
+  SmallString<128> LibclcPath(D.ResourceDir);
+  llvm::sys::path::append(LibclcPath, "lib", "libclc");
+
+  // If the namespec is of the form :filename, search for that file.
+  StringRef LibclcNamespec(A->getValue());
+  bool FilenameSearch = LibclcNamespec.consume_front(":");
+  SmallString<128> LibclcTargetFile(LibclcNamespec);
+
+  if (FilenameSearch && llvm::sys::fs::exists(LibclcTargetFile)) {
+    CC1Args.push_back("-mlink-builtin-bitcode");
+    CC1Args.push_back(DriverArgs.MakeArgString(LibclcTargetFile));
+  } else {
+    // Search the library paths for the file
+    if (!FilenameSearch)
+      LibclcTargetFile += ".bc";
+
+    llvm::sys::path::append(LibclcPath, LibclcTargetFile);
+    if (llvm::sys::fs::exists(LibclcPath)) {
+      CC1Args.push_back("-mlink-builtin-bitcode");
+      CC1Args.push_back(DriverArgs.MakeArgString(LibclcPath));
+    } else {
+      // Since the user requested a library, if we haven't one then report an
+      // error.
+      D.Diag(diag::err_drv_libclc_not_found) << LibclcTargetFile;
+    }
+  }
+}
+
 void tools::addOutlineAtomicsArgs(const Driver &D, const ToolChain &TC,
                                   const llvm::opt::ArgList &Args,
                                   llvm::opt::ArgStringList &CmdArgs,

clang/test/Driver/Inputs/libclc/libclc.bc

@@ -0,0 +1,9 @@
+// RUN: %clang -### -target amdgcn-amd-amdhsa --no-offloadlib --libclc-lib=:%S/Inputs/libclc/libclc.bc %s 2>&1 | FileCheck %s
+// RUN: %clang -### -target amdgcn-amd-amdhsa --no-offloadlib --libclc-lib=:%S/Inputs/libclc/subdir/libclc.bc %s 2>&1 | FileCheck %s --check-prefix CHECK-SUBDIR
+
+// RUN: not %clang -### -target amdgcn-amd-amdhsa --no-offloadlib --libclc-lib=:%S/Inputs/libclc/subdir/not-here.bc %s 2>&1 | FileCheck %s --check-prefix CHECK-ERROR
+
+// CHECK: -mlink-builtin-bitcode{{.*}}Inputs{{/|\\\\}}libclc{{/|\\\\}}libclc.bc
+// CHECK-SUBDIR: -mlink-builtin-bitcode{{.*}}Inputs{{/|\\\\}}libclc{{/|\\\\}}subdir{{/|\\\\}}libclc.bc
+
+// CHECK-ERROR: no libclc library{{.*}}not-here.bc' found in the clang resource directory

clang/test/Driver/Inputs/libclc/subdir/libclc.bc

@@ -73,6 +73,9 @@ if( LIBCLC_STANDALONE_BUILD OR CMAKE_SOURCE_DIR STREQUAL CMAKE_CURRENT_SOURCE_DI
       set( ${tool}_target )
     endforeach()
   endif()
+
+  # Setup the paths where libclc runtimes should be stored.
+  set( LIBCLC_OUTPUT_LIBRARY_DIR ${CMAKE_CURRENT_BINARY_DIR} )
 else()
   # In-tree configuration
   set( LIBCLC_STANDALONE_BUILD FALSE )
@@ -92,10 +95,14 @@ else()
     get_host_tool_path( llvm-link LLVM_LINK llvm-link_exe llvm-link_target )
     get_host_tool_path( opt OPT opt_exe opt_target )
   endif()
-endif()
 
-# Setup the paths where libclc runtimes should be stored.
-set( LIBCLC_OUTPUT_LIBRARY_DIR ${CMAKE_CURRENT_BINARY_DIR} )
+  # Setup the paths where libclc runtimes should be stored. By default, in an
+  # in-tree build we place the libraries in clang's resource driectory.
+  get_clang_resource_dir( LIBCLC_OUTPUT_DIR PREFIX ${LLVM_LIBRARY_OUTPUT_INTDIR}/.. )
+
+  # Note we do not adhere to LLVM_ENABLE_PER_TARGET_RUNTIME_DIR.
+  set( LIBCLC_OUTPUT_LIBRARY_DIR ${LIBCLC_OUTPUT_DIR}/lib/libclc )
+endif()
 
 if( EXISTS ${LIBCLC_CUSTOM_LLVM_TOOLS_BINARY_DIR} )
   message( WARNING "Using custom LLVM tools to build libclc: "