--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/utils/TableGen/DisassemblerEmitter.cpp	Thu Dec 12 13:56:28 2013 +0900
@@ -0,0 +1,146 @@
+//===- DisassemblerEmitter.cpp - Generate a disassembler ------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+#include "CodeGenTarget.h"
+#include "X86DisassemblerTables.h"
+#include "X86RecognizableInstr.h"
+#include "llvm/TableGen/Error.h"
+#include "llvm/TableGen/Record.h"
+#include "llvm/TableGen/TableGenBackend.h"
+
+using namespace llvm;
+using namespace llvm::X86Disassembler;
+
+/// DisassemblerEmitter - Contains disassembler table emitters for various
+/// architectures.
+
+/// X86 Disassembler Emitter
+///
+/// *** IF YOU'RE HERE TO RESOLVE A "Primary decode conflict", LOOK DOWN NEAR
+///     THE END OF THIS COMMENT!
+///
+/// The X86 disassembler emitter is part of the X86 Disassembler, which is
+/// documented in lib/Target/X86/X86Disassembler.h.
+///
+/// The emitter produces the tables that the disassembler uses to translate
+/// instructions.  The emitter generates the following tables:
+///
+/// - One table (CONTEXTS_SYM) that contains a mapping of attribute masks to
+///   instruction contexts.  Although for each attribute there are cases where
+///   that attribute determines decoding, in the majority of cases decoding is
+///   the same whether or not an attribute is present.  For example, a 64-bit
+///   instruction with an OPSIZE prefix and an XS prefix decodes the same way in
+///   all cases as a 64-bit instruction with only OPSIZE set.  (The XS prefix
+///   may have effects on its execution, but does not change the instruction
+///   returned.)  This allows considerable space savings in other tables.
+/// - Six tables (ONEBYTE_SYM, TWOBYTE_SYM, THREEBYTE38_SYM, THREEBYTE3A_SYM,
+///   THREEBYTEA6_SYM, and THREEBYTEA7_SYM contain the hierarchy that the
+///   decoder traverses while decoding an instruction.  At the lowest level of
+///   this hierarchy are instruction UIDs, 16-bit integers that can be used to
+///   uniquely identify the instruction and correspond exactly to its position
+///   in the list of CodeGenInstructions for the target.
+/// - One table (INSTRUCTIONS_SYM) contains information about the operands of
+///   each instruction and how to decode them.
+///
+/// During table generation, there may be conflicts between instructions that
+/// occupy the same space in the decode tables.  These conflicts are resolved as
+/// follows in setTableFields() (X86DisassemblerTables.cpp)
+///
+/// - If the current context is the native context for one of the instructions
+///   (that is, the attributes specified for it in the LLVM tables specify
+///   precisely the current context), then it has priority.
+/// - If the current context isn't native for either of the instructions, then
+///   the higher-priority context wins (that is, the one that is more specific).
+///   That hierarchy is determined by outranks() (X86DisassemblerTables.cpp)
+/// - If the current context is native for both instructions, then the table
+///   emitter reports a conflict and dies.
+///
+/// *** RESOLUTION FOR "Primary decode conflict"S
+///
+/// If two instructions collide, typically the solution is (in order of
+/// likelihood):
+///
+/// (1) to filter out one of the instructions by editing filter()
+///     (X86RecognizableInstr.cpp).  This is the most common resolution, but
+///     check the Intel manuals first to make sure that (2) and (3) are not the
+///     problem.
+/// (2) to fix the tables (X86.td and its subsidiaries) so the opcodes are
+///     accurate.  Sometimes they are not.
+/// (3) to fix the tables to reflect the actual context (for example, required
+///     prefixes), and possibly to add a new context by editing
+///     lib/Target/X86/X86DisassemblerDecoderCommon.h.  This is unlikely to be
+///     the cause.
+///
+/// DisassemblerEmitter.cpp contains the implementation for the emitter,
+///   which simply pulls out instructions from the CodeGenTarget and pushes them
+///   into X86DisassemblerTables.
+/// X86DisassemblerTables.h contains the interface for the instruction tables,
+///   which manage and emit the structures discussed above.
+/// X86DisassemblerTables.cpp contains the implementation for the instruction
+///   tables.
+/// X86ModRMFilters.h contains filters that can be used to determine which
+///   ModR/M values are valid for a particular instruction.  These are used to
+///   populate ModRMDecisions.
+/// X86RecognizableInstr.h contains the interface for a single instruction,
+///   which knows how to translate itself from a CodeGenInstruction and provide
+///   the information necessary for integration into the tables.
+/// X86RecognizableInstr.cpp contains the implementation for a single
+///   instruction.
+
+namespace llvm {
+
+extern void EmitFixedLenDecoder(RecordKeeper &RK, raw_ostream &OS,
+                                std::string PredicateNamespace,
+                                std::string GPrefix,
+                                std::string GPostfix,
+                                std::string ROK,
+                                std::string RFail,
+                                std::string L);
+
+void EmitDisassembler(RecordKeeper &Records, raw_ostream &OS) {
+  CodeGenTarget Target(Records);
+  emitSourceFileHeader(" * " + Target.getName() + " Disassembler", OS);
+
+  // X86 uses a custom disassembler.
+  if (Target.getName() == "X86") {
+    DisassemblerTables Tables;
+
+    const std::vector<const CodeGenInstruction*> &numberedInstructions =
+      Target.getInstructionsByEnumValue();
+
+    for (unsigned i = 0, e = numberedInstructions.size(); i != e; ++i)
+      RecognizableInstr::processInstr(Tables, *numberedInstructions[i], i);
+
+    if (Tables.hasConflicts())
+      PrintFatalError(Target.getTargetRecord()->getLoc(),
+                      "Primary decode conflict");
+
+    Tables.emit(OS);
+    return;
+  }
+
+  // ARM and Thumb have a CHECK() macro to deal with DecodeStatuses.
+  if (Target.getName() == "ARM" ||
+      Target.getName() == "Thumb" || 
+      Target.getName() == "AArch64") {
+    EmitFixedLenDecoder(Records, OS, Target.getName() == "AArch64" ? "AArch64" : "ARM",
+                        "if (!Check(S, ", ")) return MCDisassembler::Fail;",
+                        "S", "MCDisassembler::Fail",
+                        "  MCDisassembler::DecodeStatus S = "
+                          "MCDisassembler::Success;\n(void)S;");
+    return;
+  }
+
+  EmitFixedLenDecoder(Records, OS, Target.getName(),
+                      "if (", " == MCDisassembler::Fail)"
+                       " return MCDisassembler::Fail;",
+                      "MCDisassembler::Success", "MCDisassembler::Fail", "");
+}
+
+} // End llvm namespace