utils/TableGen/DisassemblerEmitter.cpp

   1 //===- DisassemblerEmitter.cpp - Generate a disassembler ------------------===//
   2 //
   3 //                     The LLVM Compiler Infrastructure
   4 //
   5 // This file is distributed under the University of Illinois Open Source
   6 // License. See LICENSE.TXT for details.
   7 //
   8 //===----------------------------------------------------------------------===//
   9
  10 #include "DisassemblerEmitter.h"
  11 #include "CodeGenTarget.h"
  12 #include "Record.h"
  13 #include "X86DisassemblerTables.h"
  14 #include "X86RecognizableInstr.h"
  15 #include "ARMDecoderEmitter.h"
  16
  17 using namespace llvm;
  18 using namespace llvm::X86Disassembler;
  19
  20 /// DisassemblerEmitter - Contains disassembler table emitters for various
  21 /// architectures.
  22
  23 /// X86 Disassembler Emitter
  24 ///
  25 /// *** IF YOU'RE HERE TO RESOLVE A "Primary decode conflict", LOOK DOWN NEAR
  26 ///     THE END OF THIS COMMENT!
  27 ///
  28 /// The X86 disassembler emitter is part of the X86 Disassembler, which is
  29 /// documented in lib/Target/X86/X86Disassembler.h.
  30 ///
  31 /// The emitter produces the tables that the disassembler uses to translate
  32 /// instructions.  The emitter generates the following tables:
  33 ///
  34 /// - One table (CONTEXTS_SYM) that contains a mapping of attribute masks to
  35 ///   instruction contexts.  Although for each attribute there are cases where
  36 ///   that attribute determines decoding, in the majority of cases decoding is
  37 ///   the same whether or not an attribute is present.  For example, a 64-bit
  38 ///   instruction with an OPSIZE prefix and an XS prefix decodes the same way in
  39 ///   all cases as a 64-bit instruction with only OPSIZE set.  (The XS prefix
  40 ///   may have effects on its execution, but does not change the instruction
  41 ///   returned.)  This allows considerable space savings in other tables.
  42 /// - Four tables (ONEBYTE_SYM, TWOBYTE_SYM, THREEBYTE38_SYM, and
  43 ///   THREEBYTE3A_SYM) contain the hierarchy that the decoder traverses while
  44 ///   decoding an instruction.  At the lowest level of this hierarchy are
  45 ///   instruction UIDs, 16-bit integers that can be used to uniquely identify
  46 ///   the instruction and correspond exactly to its position in the list of
  47 ///   CodeGenInstructions for the target.
  48 /// - One table (INSTRUCTIONS_SYM) contains information about the operands of
  49 ///   each instruction and how to decode them.
  50 ///
  51 /// During table generation, there may be conflicts between instructions that
  52 /// occupy the same space in the decode tables.  These conflicts are resolved as
  53 /// follows in setTableFields() (X86DisassemblerTables.cpp)
  54 ///
  55 /// - If the current context is the native context for one of the instructions
  56 ///   (that is, the attributes specified for it in the LLVM tables specify
  57 ///   precisely the current context), then it has priority.
  58 /// - If the current context isn't native for either of the instructions, then
  59 ///   the higher-priority context wins (that is, the one that is more specific).
  60 ///   That hierarchy is determined by outranks() (X86DisassemblerTables.cpp)
  61 /// - If the current context is native for both instructions, then the table
  62 ///   emitter reports a conflict and dies.
  63 ///
  64 /// *** RESOLUTION FOR "Primary decode conflict"S
  65 ///
  66 /// If two instructions collide, typically the solution is (in order of
  67 /// likelihood):
  68 ///
  69 /// (1) to filter out one of the instructions by editing filter()
  70 ///     (X86RecognizableInstr.cpp).  This is the most common resolution, but
  71 ///     check the Intel manuals first to make sure that (2) and (3) are not the
  72 ///     problem.
  73 /// (2) to fix the tables (X86.td and its subsidiaries) so the opcodes are
  74 ///     accurate.  Sometimes they are not.
  75 /// (3) to fix the tables to reflect the actual context (for example, required
  76 ///     prefixes), and possibly to add a new context by editing
  77 ///     lib/Target/X86/X86DisassemblerDecoderCommon.h.  This is unlikely to be
  78 ///     the cause.
  79 ///
  80 /// DisassemblerEmitter.cpp contains the implementation for the emitter,
  81 ///   which simply pulls out instructions from the CodeGenTarget and pushes them
  82 ///   into X86DisassemblerTables.
  83 /// X86DisassemblerTables.h contains the interface for the instruction tables,
  84 ///   which manage and emit the structures discussed above.
  85 /// X86DisassemblerTables.cpp contains the implementation for the instruction
  86 ///   tables.
  87 /// X86ModRMFilters.h contains filters that can be used to determine which
  88 ///   ModR/M values are valid for a particular instruction.  These are used to
  89 ///   populate ModRMDecisions.
  90 /// X86RecognizableInstr.h contains the interface for a single instruction,
  91 ///   which knows how to translate itself from a CodeGenInstruction and provide
  92 ///   the information necessary for integration into the tables.
  93 /// X86RecognizableInstr.cpp contains the implementation for a single
  94 ///   instruction.
  95
  96 void DisassemblerEmitter::run(raw_ostream &OS) {
  97   CodeGenTarget Target(Records);
  98
  99   OS << "/*===- TableGen'erated file "
 100      << "---------------------------------------*- C -*-===*\n"
 101      << " *\n"
 102      << " * " << Target.getName() << " Disassembler\n"
 103      << " *\n"
 104      << " * Automatically generated file, do not edit!\n"
 105      << " *\n"
 106      << " *===---------------------------------------------------------------"
 107      << "-------===*/\n";
 108
 109   // X86 uses a custom disassembler.
 110   if (Target.getName() == "X86") {
 111     DisassemblerTables Tables;
 112
 113     const std::vector<const CodeGenInstruction*> &numberedInstructions =
 114       Target.getInstructionsByEnumValue();
 115
 116     for (unsigned i = 0, e = numberedInstructions.size(); i != e; ++i)
 117       RecognizableInstr::processInstr(Tables, *numberedInstructions[i], i);
 118
 119     // FIXME: As long as we are using exceptions, might as well drop this to the
 120     // actual conflict site.
 121     if (Tables.hasConflicts())
 122       throw TGError(Target.getTargetRecord()->getLoc(),
 123                     "Primary decode conflict");
 124
 125     Tables.emit(OS);
 126     return;
 127   }
 128
 129   // Fixed-instruction-length targets use a common disassembler.
 130   if (Target.getName() == "ARM") {
 131     ARMDecoderEmitter(Records).run(OS);
 132     return;
 133   }
 134
 135   throw TGError(Target.getTargetRecord()->getLoc(),
 136                 "Unable to generate disassembler for this target");
 137 }