Write llvm-tblgen backends as functions instead of sub-classes.

The TableGenBackend base class doesn't do much, and will be removed
completely soon.

Patch by Sean Silva!

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@158311 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 78 insertions, 0 deletions

diff --git a/utils/TableGen/TableGenBackends.h b/utils/TableGen/TableGenBackends.h
new file mode 100644
index 0000000000..2c00c40cfe
--- /dev/null
+++ b/utils/TableGen/TableGenBackends.h
@@ -0,0 +1,78 @@
+//===- TableGenBackends.h - Declarations for LLVM TableGen Backends -------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This file contains the declarations for all of the LLVM TableGen
+// backends. A "TableGen backend" is just a function. See below for a
+// precise description.
+//
+//===----------------------------------------------------------------------===//
+
+
+// A TableGen backend is a function that looks like
+//
+//    EmitFoo(RecordKeeper &RK, raw_ostream &OS /*, anything else you need */ )
+//
+// What you do inside of that function is up to you, but it will usually
+// involve generating C++ code to the provided raw_ostream.
+//
+// The RecordKeeper is just a top-level container for an in-memory
+// representation of the data encoded in the TableGen file. What a TableGen
+// backend does is walk around that in-memory representation and generate
+// stuff based on the information it contains.
+//
+// The in-memory representation is a node-graph (think of it like JSON but
+// with a richer ontology of types), where the nodes are subclasses of
+// Record. The methods `getClass`, `getDef` are the basic interface to
+// access the node-graph.  RecordKeeper also provides a handy method
+// `getAllDerivedDefinitions`. Consult "include/llvm/TableGen/Record.h" for
+// the exact interfaces provided by Record's and RecordKeeper.
+//
+// A common pattern for TableGen backends is for the EmitFoo function to
+// instantiate a class which holds some context for the generation process,
+// and then have most of the work happen in that class's methods. This
+// pattern partly has historical roots in the previous TableGen backend API
+// that involved a class and an invocation like `FooEmitter(RK).run(OS)`.
+//
+// Remember to wrap private things in an anonymous namespace. For most
+// backends, this means that the EmitFoo function is the only thing not in
+// the anonymous namespace.
+
+
+// FIXME: Reorganize TableGen so that build dependencies can be more
+// accurately expressed. Currently, touching any of the emitters (or
+// anything that they transitively depend on) causes everything dependent
+// on TableGen to be rebuilt (this includes all the targets!). Perhaps have
+// a standalone TableGen binary and have the backends be loadable modules
+// of some sort; then the dependency could be expressed as being on the
+// module, and all the modules would have a common dependency on the
+// TableGen binary with as few dependencies as possible on the rest of
+// LLVM.
+
+
+namespace llvm {
+
+class raw_ostream;
+class RecordKeeper;
+
+void EmitIntrinsics(RecordKeeper &RK, raw_ostream &OS, bool TargetOnly = false);
+void EmitAsmMatcher(RecordKeeper &RK, raw_ostream &OS);
+void EmitAsmWriter(RecordKeeper &RK, raw_ostream &OS);
+void EmitCallingConv(RecordKeeper &RK, raw_ostream &OS);
+void EmitCodeEmitter(RecordKeeper &RK, raw_ostream &OS);
+void EmitDAGISel(RecordKeeper &RK, raw_ostream &OS);
+void EmitDFAPacketizer(RecordKeeper &RK, raw_ostream &OS);
+void EmitDisassembler(RecordKeeper &RK, raw_ostream &OS);
+void EmitEnhancedDisassemblerInfo(RecordKeeper &RK, raw_ostream &OS);
+void EmitFastISel(RecordKeeper &RK, raw_ostream &OS);
+void EmitInstrInfo(RecordKeeper &RK, raw_ostream &OS);
+void EmitPseudoLowering(RecordKeeper &RK, raw_ostream &OS);
+void EmitRegisterInfo(RecordKeeper &RK, raw_ostream &OS);
+void EmitSubtarget(RecordKeeper &RK, raw_ostream &OS);
+
+} // End llvm namespace