[Clang] Added options for integrated backend.

Following the new flow for external object code emission,
provide flags to switch between integrated and external
backend similar to the integrated assembler options.

SPIR-V target is the only user of this functionality at
this point.

This patch also updated SPIR-V documentation to clarify
that integrated object code emission for SPIR-V is an
experimental feature.

Differential Revision: https://reviews.llvm.org/D125679

clang/docs/UsersManual.rst

@@ -3180,8 +3180,8 @@ Generic Targets
 
    .. code-block:: console
 
-    $ clang -target spirv32 test.cl
-    $ clang -target spirv64 test.cl
+    $ clang -target spirv32 -c test.cl
+    $ clang -target spirv64 -c test.cl
 
   More details can be found in :ref:`the SPIR-V support section <spir-v>`.
 
@@ -3657,8 +3657,8 @@ Example usage for OpenCL kernel compilation:
 
    .. code-block:: console
 
-     $ clang -target spirv32 test.cl
-     $ clang -target spirv64 test.cl
+     $ clang -target spirv32 -c test.cl
+     $ clang -target spirv64 -c test.cl
 
 Both invocations of Clang will result in the generation of a SPIR-V binary file
 `test.o` for 32 bit and 64 bit respectively. This file can be imported
@@ -3669,6 +3669,18 @@ Converting to SPIR-V produced with the optimization levels other than `-O0` is
 currently available as an experimental feature and it is not guaranteed to work
 in all cases.
 
+Clang also supports integrated generation of SPIR-V without use of ``llvm-spirv``
+tool as an experimental feature when ``-fintegrated-objemitter`` flag is passed in
+the command line.
+
+   .. code-block:: console
+
+     $ clang -target spirv32 -fintegrated-objemitter -c test.cl
+
+Note that only very basic functionality is supported at this point and therefore
+it is not suitable for arbitrary use cases. This feature is only enabled when clang
+build is configured with ``-DLLVM_EXPERIMENTAL_TARGETS_TO_BUILD=SPIRV`` option.
+
 Linking is done using ``spirv-link`` from `the SPIRV-Tools project
 <https://github.com/KhronosGroup/SPIRV-Tools#linker>`_. Similar to other external
 linkers, Clang will expect ``spirv-link`` to be installed separately and to be
@@ -3676,6 +3688,10 @@ present in the ``PATH`` environment variable. Please refer to `the build and
 installation instructions
 <https://github.com/KhronosGroup/SPIRV-Tools#build>`_.
 
+   .. code-block:: console
+
+     $ clang -target spirv64 test1.cl test2.cl
+
 .. _clang-cl:
 
 clang-cl

clang/include/clang/Driver/Options.td

@@ -4170,6 +4170,13 @@ def fno_integrated_cc1 : Flag<["-"], "fno-integrated-cc1">,
                          Flags<[CoreOption, NoXarchOption]>, Group<f_Group>,
                          HelpText<"Spawn a separate process for each cc1">;
 
+def fintegrated_objemitter : Flag<["-"], "fintegrated-objemitter">,
+  Flags<[CoreOption, NoXarchOption]>, Group<f_Group>,
+  HelpText<"Use internal machine object code emitter.">;
+def fno_integrated_objemitter : Flag<["-"], "fno-integrated-objemitter">,
+  Flags<[CoreOption, NoXarchOption]>, Group<f_Group>,
+  HelpText<"Use external machine object code emitter.">;
+
 def : Flag<["-"], "integrated-as">, Alias<fintegrated_as>, Flags<[NoXarchOption]>;
 def : Flag<["-"], "no-integrated-as">, Alias<fno_integrated_as>,
       Flags<[CC1Option, FlangOption, NoXarchOption]>;

clang/include/clang/Driver/ToolChain.h

@@ -385,11 +385,23 @@ public:
   /// by default.
   virtual bool IsIntegratedAssemblerDefault() const { return false; }
 
+  /// IsIntegratedBackendDefault - Does this tool chain enable
+  /// -fintegrated-objemitter by default.
+  virtual bool IsIntegratedBackendDefault() const { return true; }
+
+  /// IsIntegratedBackendSupported - Does this tool chain support
+  /// -fintegrated-objemitter.
+  virtual bool IsIntegratedBackendSupported() const { return true; }
+
+  /// IsNonIntegratedBackendSupported - Does this tool chain support
+  /// -fno-integrated-objemitter.
+  virtual bool IsNonIntegratedBackendSupported() const { return false; }
+
   /// Check if the toolchain should use the integrated assembler.
   virtual bool useIntegratedAs() const;
 
   /// Check if the toolchain should use the integrated backend.
-  virtual bool useIntegratedBackend() const { return true; }
+  virtual bool useIntegratedBackend() const;
 
   /// Check if the toolchain should use AsmParser to parse inlineAsm when
   /// integrated assembler is not default.

clang/lib/Driver/ToolChain.cpp

@@ -106,6 +106,34 @@ bool ToolChain::useIntegratedAs() const {
                       IsIntegratedAssemblerDefault());
 }
 
+bool ToolChain::useIntegratedBackend() const {
+  assert(
+      ((IsIntegratedBackendDefault() && IsIntegratedBackendSupported()) ||
+       (!IsIntegratedBackendDefault() || IsNonIntegratedBackendSupported())) &&
+      "(Non-)integrated backend set incorrectly!");
+
+  bool IBackend = Args.hasFlag(options::OPT_fintegrated_objemitter,
+                               options::OPT_fno_integrated_objemitter,
+                               IsIntegratedBackendDefault());
+
+  // Diagnose when integrated-objemitter options are not supported by this
+  // toolchain.
+  unsigned DiagID;
+  if ((IBackend && !IsIntegratedBackendSupported()) ||
+      (!IBackend && !IsNonIntegratedBackendSupported()))
+    DiagID = clang::diag::err_drv_unsupported_opt_for_target;
+  else
+    DiagID = clang::diag::warn_drv_unsupported_opt_for_target;
+  Arg *A = Args.getLastArg(options::OPT_fno_integrated_objemitter);
+  if (A && !IsNonIntegratedBackendSupported())
+    D.Diag(DiagID) << A->getAsString(Args) << Triple.getTriple();
+  A = Args.getLastArg(options::OPT_fintegrated_objemitter);
+  if (A && !IsIntegratedBackendSupported())
+    D.Diag(DiagID) << A->getAsString(Args) << Triple.getTriple();
+
+  return IBackend;
+}
+
 bool ToolChain::useRelaxRelocations() const {
   return ENABLE_X86_RELAX_RELOCATIONS;
 }

clang/lib/Driver/ToolChains/SPIRV.h

@@ -64,8 +64,9 @@ public:
       : ToolChain(D, Triple, Args) {}
 
   bool useIntegratedAs() const override { return true; }
-  bool useIntegratedBackend() const override { return false; }
 
+  bool IsIntegratedBackendDefault() const override { return false; }
+  bool IsNonIntegratedBackendSupported() const override { return true; }
   bool IsMathErrnoDefault() const override { return false; }
   bool isCrossCompiling() const override { return true; }
   bool isPICDefault() const override { return false; }

clang/test/Driver/clang_f_opts.c

@@ -605,3 +605,8 @@
 // CHECK_JMC_WARN_NOT_ELF: -fjmc works only for ELF; option ignored
 // CHECK_NOJMC-NOT: -fjmc
 // CHECK_JMC: -fjmc
+
+// RUN: %clang -### -fintegrated-objemitter -target x86_64 %s 2>&1 | FileCheck -check-prefix=CHECK-INT-OBJEMITTER %s
+// CHECK-INT-OBJEMITTER-NOT: unsupported option '-fintegrated-objemitter' for target
+// RUN: %clang -### -fno-integrated-objemitter -target x86_64 %s 2>&1 | FileCheck -check-prefix=CHECK-NOINT-OBJEMITTER %s
+// CHECK-NOINT-OBJEMITTER: unsupported option '-fno-integrated-objemitter' for target

clang/test/Driver/spirv-toolchain.cl

@@ -69,3 +69,11 @@
 // SPLINK-SAME: "-o" [[BC:".*bc"]]
 // SPLINK: {{llvm-spirv.*"}} [[BC]] "-o" [[SPV2:".*o"]]
 // SPLINK: {{spirv-link.*"}} [[SPV1]] [[SPV2]] "-o" "a.out"
+
+//-----------------------------------------------------------------------------
+// Check external vs internal object emission.
+// RUN: %clang -### --target=spirv64 -fno-integrated-objemitter %s 2>&1 | FileCheck --check-prefix=XTOR %s
+// RUN: %clang -### --target=spirv64 -fintegrated-objemitter %s 2>&1 | FileCheck --check-prefix=BACKEND %s
+
+// XTOR: {{llvm-spirv.*"}}
+// BACKEND-NOT: {{llvm-spirv.*"}}