[BACKEND][CODEGEN] C codegen with tests (apache#2161)

* Implement C code generation with tests

* Code cleanup

* Implement C code generation with tests

* Code cleanup

* tabs to spaces

* make lint compliant

* update export_library and reserve unique C keywords

* move ReserveKeywordsAsUnique to codegen_c

* some documentation and code cleanup

* use tvm.contrib.util for tempdir in testcases

python/tvm/_ffi/libinfo.py

@@ -99,6 +99,66 @@ def find_lib_path(name=None, search_path=None, optional=False):
     return lib_found
 
 
+def find_include_path(name=None, search_path=None, optional=False):
+    """Find header files for C compilation.
+
+    Parameters
+    ----------
+    name : list of str
+        List of directory names to be searched.
+
+    Returns
+    -------
+    include_path : list(string)
+        List of all found paths to header files.
+    """
+    ffi_dir = os.path.dirname(os.path.abspath(os.path.expanduser(__file__)))
+    source_dir = os.path.join(ffi_dir, "..", "..", "..")
+    install_include_dir = os.path.join(ffi_dir, "..", "..", "..", "..")
+    third_party_dir = os.path.join(source_dir, "3rdparty")
+
+    header_path = []
+
+    if os.environ.get('TVM_INCLUDE_PATH', None):
+        header_path.append(os.environ['TVM_INCLUDE_PATH'])
+
+    header_path.append(install_include_dir)
+    header_path.append(source_dir)
+    header_path.append(third_party_dir)
+
+    header_path = [os.path.abspath(x) for x in header_path]
+    if search_path is not None:
+        if search_path is list:
+            header_path = header_path + search_path
+        else:
+            header_path.append(search_path)
+    if name is not None:
+        if isinstance(name, list):
+            tvm_include_path = []
+            for n in name:
+                tvm_include_path += [os.path.join(p, n) for p in header_path]
+        else:
+            tvm_include_path = [os.path.join(p, name) for p in header_path]
+        dlpack_include_path = []
+    else:
+        tvm_include_path = [os.path.join(p, 'include') for p in header_path]
+        dlpack_include_path = [os.path.join(p, 'dlpack/include') for p in header_path]
+
+        # try to find include path
+        include_found = [p for p in tvm_include_path if os.path.exists(p) and os.path.isdir(p)]
+        include_found += [p for p in dlpack_include_path if os.path.exists(p) and os.path.isdir(p)]
+
+    if not include_found:
+        message = ('Cannot find the files.\n' +
+                   'List of candidates:\n' +
+                   str('\n'.join(tvm_include_path + dlpack_include_path)))
+        if not optional:
+            raise RuntimeError(message)
+        return None
+
+    return include_found
+
+
 # current version
 # We use the version of the incoming release for code
 # that is under development.

python/tvm/_ffi/runtime_ctypes.py

@@ -118,6 +118,7 @@ class TVMContext(ctypes.Structure):
         'llvm': 1,
         'stackvm': 1,
         'cpu': 1,
+        'c': 1,
         'gpu': 2,
         'cuda': 2,
         'nvptx': 2,

python/tvm/contrib/cc.py

@@ -7,6 +7,7 @@
 
 from .._ffi.base import py_str
 from .util import tempdir
+from .._ffi.libinfo import find_include_path
 
 
 def create_shared(output,
@@ -49,6 +50,7 @@ def _linux_shared(output, objects, options, cc="g++"):
         cmd += objects
     if options:
         cmd += options
+    cmd += ["-I" + path for path in find_include_path()]
     proc = subprocess.Popen(
         cmd, stdout=subprocess.PIPE, stderr=subprocess.STDOUT)
     (out, _) = proc.communicate()

python/tvm/module.py

@@ -115,17 +115,21 @@ def export_library(self,
             self.save(file_name)
             return
 
-        if self.type_key != "llvm":
-            raise ValueError("Module[%s]: Only llvm support export shared" % self.type_key)
+        if not (self.type_key == "llvm" or self.type_key == "c"):
+            raise ValueError("Module[%s]: Only llvm and c support export shared" % self.type_key)
         temp = _util.tempdir()
         if fcompile is not None and hasattr(fcompile, "object_format"):
             object_format = fcompile.object_format
         else:
-            object_format = "o"
+            if self.type_key == "llvm":
+                object_format = "o"
+            else:
+                assert self.type_key == "c"
+                object_format = "cc"
         path_obj = temp.relpath("lib." + object_format)
         self.save(path_obj)
         files = [path_obj]
-        is_system_lib = self.get_function("__tvm_is_system_module")()
+        is_system_lib = self.type_key == "llvm" and self.get_function("__tvm_is_system_module")()
         if self.imported_modules:
             path_cc = temp.relpath("devc.cc")
             with open(path_cc, "w") as f:

src/codegen/codegen_c.cc

@@ -22,12 +22,43 @@ void CodeGenC::InitFuncState(LoweredFunc f) {
   handle_data_type_.clear();
   CodeGenSourceBase::ClearFuncState();
 }
-void CodeGenC::AddFunction(LoweredFunc f) {
-  // clear previous generated state.
-  this->InitFuncState(f);
+
+void CodeGenC::ReserveKeywordsAsUnique() {
   // skip the first underscore, so SSA variable starts from _1
   GetUniqueName("_");
   GetUniqueName("extern");
+  GetUniqueName("void");
+  GetUniqueName("int");
+  GetUniqueName("float");
+  GetUniqueName("double");
+  GetUniqueName("char");
+  GetUniqueName("unsigned");
+  GetUniqueName("short");
+  GetUniqueName("long");
+  GetUniqueName("if");
+  GetUniqueName("else");
+  GetUniqueName("switch");
+  GetUniqueName("case");
+  GetUniqueName("default");
+  GetUniqueName("for");
+  GetUniqueName("do");
+  GetUniqueName("while");
+  GetUniqueName("goto");
+  GetUniqueName("register");
+  GetUniqueName("continue");
+  GetUniqueName("break");
+  GetUniqueName("typedef");
+  GetUniqueName("struct");
+  GetUniqueName("enum");
+  GetUniqueName("union");
+  GetUniqueName("return");
+}
+
+void CodeGenC::AddFunction(LoweredFunc f) {
+  // clear previous generated state.
+  this->InitFuncState(f);
+  // reserve keywords
+  ReserveKeywordsAsUnique();
   // add to alloc buffer type.
   for (const auto & kv : f->handle_data_type) {
     RegisterHandleType(kv.first.get(), kv.second.type());
@@ -187,6 +218,7 @@ std::string CodeGenC::GetStructRef(
       case intrinsic::kArrNDim: os << "ndim"; break;
       case intrinsic::kArrTypeCode: os << "dtype.code"; break;
       case intrinsic::kArrTypeBits: os << "dtype.bits"; break;
+      case intrinsic::kArrByteOffset: os << "byte_offset"; break;
       case intrinsic::kArrTypeLanes: os << "dtype.lanes"; break;
       case intrinsic::kArrDeviceId: os << "ctx.device_id"; break;
       case intrinsic::kArrDeviceType: os << "ctx.device_type"; break;
@@ -834,8 +866,10 @@ void CodeGenC::VisitStmt_(const Evaluate *op) {
     }
   }
   std::string vid = this->PrintExpr(op->value);
-  this->PrintIndent();
-  this->stream << "(void)" << vid << ";\n";
+  if (vid != "") {
+    this->PrintIndent();
+    this->stream << "(void)" << vid << ";\n";
+  }
 }
 
 void CodeGenC::VisitStmt_(const ProducerConsumer *op) {

src/codegen/codegen_c.h

@@ -183,6 +183,8 @@ class CodeGenC :
   std::unordered_map<const Variable*, std::string> alloc_storage_scope_;
   /*! \brief the data type of allocated buffers */
   std::unordered_map<const Variable*, Type> handle_data_type_;
+  /*! \brief reserves common C keywords */
+  void ReserveKeywordsAsUnique();
 
  private:
   /*! \brief whether to print in SSA form */