Minor tweak to forgo the the curly braces for most case blocks, except when

declaring local variables.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@85467 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 1158 insertions, 0 deletions

diff --git a/utils/TableGen/RISCDisassemblerEmitter.cpp b/utils/TableGen/RISCDisassemblerEmitter.cpp
new file mode 100644
index 0000000000..3ef697ccb8
--- /dev/null
+++ b/utils/TableGen/RISCDisassemblerEmitter.cpp
@@ -0,0 +1,1158 @@
+//===- RISCDisassemblerEmitter.cpp - Disassembler Generator ---------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// FIXME: document
+//
+//===----------------------------------------------------------------------===//
+
+#include "RISCDisassemblerEmitter.h"
+#include "CodeGenTarget.h"
+#include "Record.h"
+#include "llvm/ADT/StringExtras.h"
+#include "llvm/Support/Debug.h"
+
+#include <iostream>
+#include <iomanip>
+#include <vector>
+#include <cstdio>
+#include <map>
+#include <string>
+#include <sstream>
+
+#include <asl.h>
+
+using namespace llvm;
+
+#pragma mark Utility classes / structures
+
+// LLVM coding style
+#define INDENT_LEVEL 2
+
+class Indenter {
+public:
+  Indenter() : fDepth(0) {
+    memset(fString, ' ', sizeof(fString));
+    fString[fDepth] = '\0';
+  }
+
+  void push() {
+    if (fDepth < sizeof(fString) - INDENT_LEVEL) {
+      fString[fDepth] = ' ';
+      fDepth += INDENT_LEVEL;
+      fString[fDepth] = '\0';
+    }
+  }
+
+  void pop() {
+    if(fDepth >= INDENT_LEVEL) {
+      fString[fDepth] = ' ';
+      fDepth -= INDENT_LEVEL;
+      fString[fDepth] = '\0';
+    }
+  }
+
+  const char* indent() const {
+    return &fString[0];
+  }
+private:
+  char fString[256];
+  uint8_t fDepth;
+};
+
+#pragma mark Utility functions
+
+#if 0
+static int dprintf(int level, const char* format, ...) throw() {
+  static aslmsg* fMessage = NULL;
+
+  if (!fMessage) {
+    fMessage = new aslmsg;
+    *fMessage = asl_new(ASL_TYPE_MSG);
+    asl_set(*fMessage, ASL_KEY_FACILITY, "com.apple.llvm.disassembler.emitter.risc");
+  }
+
+  va_list ap;
+
+  va_start(ap, format);
+  int ret = asl_vlog(NULL, *fMessage, level, format, ap);
+  va_end(ap);
+
+  return ret;
+}
+#endif
+
+static uint8_t byteFromBitsInit(BitsInit& init) {
+  int width = init.getNumBits();
+
+  assert(width <= 8 && "Field is too large for uint8_t!");
+
+  int index;
+  uint8_t mask = 0x01;
+
+  uint8_t ret = 0;
+
+  for (index = 0; index < width; index++) {
+    if (static_cast<BitInit*>(init.getBit(index))->getValue())
+      ret |= mask;
+
+    mask <<= 1;
+  }
+
+  return ret;
+}
+
+static uint8_t getByteField(const Record& def, const char* str) {
+  BitsInit* bits = def.getValueAsBitsInit(str);
+  return byteFromBitsInit(*bits);
+}
+
+static BitsInit& getBitsField(const Record& def, const char* str) {
+  BitsInit* bits = def.getValueAsBitsInit(str);
+  return *bits;
+}
+
+#if 0
+static void binaryFromNumber(std::string& binary,
+                             uint64_t number,
+                             unsigned minimumWidth = 1) {
+  unsigned bitIndex;
+  bool emitting = false;
+
+  binary = "0b";
+
+  for (bitIndex = (sizeof(number) * 8); bitIndex > 0; bitIndex--) {
+    uint64_t bit = (number & (1 << (bitIndex - 1))) >> (bitIndex - 1);
+
+    if (bitIndex == minimumWidth)
+      emitting = true;
+
+    if (bit) {
+      emitting = true;
+      binary.append("1");
+    } else if(emitting) {
+      binary.append("0");
+    }
+  }
+}
+#endif
+
+// The set (BIT_TRUE, BIT_FALSE, BIT_UNSET) represents a ternary logic system
+// for a bit value.
+//
+// BIT_UNFILTERED is used as the init value for a filter position.  It is used
+// only for filter processings.
+typedef enum {
+  BIT_TRUE,      // '1'
+  BIT_FALSE,     // '0'
+  BIT_UNSET,     // '?'
+  BIT_UNFILTERED // unfiltered
+} bitValue_t;
+
+static bitValue_t bitFromBits(BitsInit& bits, unsigned index) {
+  if (BitInit* bit = dynamic_cast<BitInit*>(bits.getBit(index)))
+    return bit->getValue() ? BIT_TRUE : BIT_FALSE;
+
+  // The bit is uninitialized.
+  return BIT_UNSET;
+}
+
+static void dumpBits(std::ostream& o, BitsInit& bits) {
+  unsigned index;
+
+  for (index = bits.getNumBits(); index > 0; index--) {
+    switch (bitFromBits(bits, index - 1)) {
+    case BIT_TRUE:
+      o << "1";
+      break;
+    case BIT_FALSE:
+      o << "0";
+      break;
+    case BIT_UNSET:
+      o << "_";
+      break;
+    default:
+      assert(0 && "unexpected return value from bitFromBits");
+    }
+  }
+}
+
+#pragma mark Enums
+
+#define ARM_FORMS                   \
+  ENTRY(ARM_FORM_PSEUDO,         0) \
+  ENTRY(ARM_FORM_MULFRM,         1) \
+  ENTRY(ARM_FORM_BRFRM,          2) \
+  ENTRY(ARM_FORM_BRMISCFRM,      3) \
+  ENTRY(ARM_FORM_DPFRM,          4) \
+  ENTRY(ARM_FORM_DPSOREGFRM,     5) \
+  ENTRY(ARM_FORM_LDFRM,          6) \
+  ENTRY(ARM_FORM_STFRM,          7) \
+  ENTRY(ARM_FORM_LDMISCFRM,      8) \
+  ENTRY(ARM_FORM_STMISCFRM,      9) \
+  ENTRY(ARM_FORM_LDSTMULFRM,    10) \
+  ENTRY(ARM_FORM_ARITHMISCFRM,  11) \
+  ENTRY(ARM_FORM_EXTFRM,        12) \
+  ENTRY(ARM_FORM_VFPUNARYFRM,   13) \
+  ENTRY(ARM_FORM_VFPBINARYFRM,  14) \
+  ENTRY(ARM_FORM_VFPCONV1FRM,   15) \
+  ENTRY(ARM_FORM_VFPCONV2FRM,   16) \
+  ENTRY(ARM_FORM_VFPCONV3FRM,   17) \
+  ENTRY(ARM_FORM_VFPCONV4FRM,   18) \
+  ENTRY(ARM_FORM_VFPCONV5FRM,   19) \
+  ENTRY(ARM_FORM_VFPLDSTFRM,    20) \
+  ENTRY(ARM_FORM_VFPLDSTMULFRM, 21) \
+  ENTRY(ARM_FORM_VFPMISCFRM,    22) \
+  ENTRY(ARM_FORM_THUMBFRM,      23) \
+  ENTRY(ARM_FORM_NEONFRM,       24) \
+  ENTRY(ARM_FORM_NEONGETLNFRM,  25) \
+  ENTRY(ARM_FORM_NEONSETLNFRM,  26) \
+  ENTRY(ARM_FORM_NEONDUPFRM,    27)
+
+// ARM instruction format specifies the encoding used by the instruction.
+#define ENTRY(n, v) n = v,
+enum ARMForm {
+  ARM_FORMS
+  ARM_FORM_max
+};
+#undef ENTRY
+
+// Converts enum to const char*.
+static const char* stringWithARMForm(enum ARMForm form) {
+#define ENTRY(n, v) case n: return #n;
+  switch(form) {
+    ARM_FORMS
+  case ARM_FORM_max:
+  default:
+    return "";
+  }
+#undef ENTRY
+}
+
+static std::vector< std::vector<unsigned> > sConflicts;
+
+class AbstractFilterChooser {
+public:
+  virtual void emitTop(std::ostream& o, Indenter& i) = 0;
+};
+
+template <unsigned tBitWidth>
+class FilterChooser : public AbstractFilterChooser {
+protected:
+  // Representation of the instruction to work on.
+  typedef uint8_t insn_t[tBitWidth];
+
+  class Filter {
+  protected:
+    FilterChooser* fParent; // pointer without ownership
+    unsigned fStartBit; // the starting bit position
+    unsigned fNumBits; // number of bits to filter
+    bool fMixed; // a mixed region contains set and unset bits
+
+    // Map of well-known segment value to the set of uid's with that value. 
+    std::map<uint64_t, std::vector<unsigned> > fFilteredInstructions;
+
+    // Set of uid's with non-constant segment values.
+    std::vector<unsigned> fVariableInstructions;
+
+    // Map of well-known segment value to its delegate.
+    std::map<unsigned, FilterChooser> fSubChoosers;
+  public:
+    Filter(const Filter& f) :
+      fParent(f.fParent),
+      fStartBit(f.fStartBit),
+      fNumBits(f.fNumBits),
+      fMixed(f.fMixed),
+      fFilteredInstructions(f.fFilteredInstructions),
+      fVariableInstructions(f.fVariableInstructions),
+      fSubChoosers(f.fSubChoosers) { }
+
+    Filter(FilterChooser& parent, unsigned startBit, unsigned numBits, bool mixed) :
+      fParent(&parent),
+      fStartBit(startBit),
+      fNumBits(numBits),
+      fMixed(mixed)
+    {
+      unsigned insnIndex;
+      unsigned numInsns = fParent->fInstructionsToFilter.size();
+
+      for (insnIndex = 0; insnIndex < numInsns; insnIndex++) {
+        insn_t insn;
+
+        // Populates the insn given the uid.
+        fParent->insnWithID(insn, fParent->fInstructionsToFilter[insnIndex]);
+
+        uint64_t field;
+        // Scans the segment for possibly well-specified encoding bits.
+        bool ok = fParent->fieldFromInsn(field, insn, fStartBit, fNumBits);
+
+        if (ok) {
+          // The encoding bits are well-known.  Lets add the uid of the
+          // instruction into the bucket keyed off the constant field value.
+          fFilteredInstructions[field].push_back(fParent->fInstructionsToFilter[insnIndex]);
+        } else {
+          // Some of the encoding bit(s) are unspecfied.  This contributes to
+          // one additional member of "Variable" instructions.
+          fVariableInstructions.push_back(fParent->fInstructionsToFilter[insnIndex]);
+        }
+      }
+
+      assert((fFilteredInstructions.size() + fVariableInstructions.size() > 0)
+             && "Filter returns no instruction categories");
+    }
+
+    // Divides the decoding task into sub tasks and delegates them to the
+    // inferior FilterChooser's.
+    void recurse() {
+      std::map<uint64_t, std::vector<unsigned> >::const_iterator mapIterator;
+
+      bitValue_t filtered[tBitWidth];
+      // Starts by inheriting our parent filter chooser's bit values.
+      memcpy(filtered, fParent->fFiltered, sizeof(filtered));
+
+      unsigned bitIndex;
+
+      for (mapIterator = fFilteredInstructions.begin();
+           mapIterator != fFilteredInstructions.end();
+           mapIterator++) {
+
+        // Marks all the segment positions with either BIT_TRUE or BIT_FALSE.
+        for (bitIndex = 0; bitIndex < fNumBits; bitIndex++) {
+          if (mapIterator->first & (1 << bitIndex))
+            filtered[fStartBit + bitIndex] = BIT_TRUE;
+          else
+            filtered[fStartBit + bitIndex] = BIT_FALSE;
+        }
+
+        // Delegates to an inferior filter chooser for futher processing on this
+        // category of instructions.
+        fSubChoosers.insert(std::pair<unsigned, FilterChooser>(
+                              mapIterator->first,
+                              FilterChooser(fParent->fAllInstructions,
+                                            mapIterator->second,
+                                            filtered,
+                                            *fParent)
+                              ));
+      }
+
+      if (fVariableInstructions.size()) {
+        // Conservatively marks each segment position as BIT_UNSET.
+        for (bitIndex = 0; bitIndex < fNumBits; bitIndex++)
+          filtered[fStartBit + bitIndex] = BIT_UNSET;
+
+        // Delegates to an inferior filter chooser for futher processing on this
+        // group of instructions whose segment values are variable.
+        fSubChoosers.insert(std::pair<unsigned, FilterChooser>(
+                              (unsigned)-1,
+                              FilterChooser(fParent->fAllInstructions,
+                                            fVariableInstructions,
+                                            filtered,
+                                            *fParent)
+                              ));
+      }
+    }
+
+    // Emits code to decode instructions given a segment of bits.
+    void emit(std::ostream& o, Indenter& i) {
+      o << i.indent() << "// Check Inst{";
+
+      if (fNumBits > 1)
+        o << (fStartBit + fNumBits - 1) << '-';
+
+      o << fStartBit << "} ...\n";
+
+      o << i.indent() << "switch (fieldFromInstruction(insn, " << fStartBit << ", " << fNumBits << ")) {\n";
+      i.push();
+
+      typename std::map<unsigned, FilterChooser>::iterator filterIterator;
+
+      for (filterIterator = fSubChoosers.begin();
+           filterIterator != fSubChoosers.end();
+           filterIterator++) {
+
+        // Field value -1 implies a non-empty set of variable instructions.
+        // See also recurse().
+        if (filterIterator->first == (unsigned)-1)
+          o << i.indent() << "default:\n";
+        else
+          o << i.indent() << "case " << filterIterator->first << ":\n";
+
+        // We arrive at a category of instructions with the same segment value.
+        // Now delegate to the sub filter chooser for further decodings.
+        i.push();
+        {
+          bool finished = filterIterator->second.emit(o, i);
+          if (!finished) o << i.indent() << "break;\n";
+        }
+        i.pop();
+      }
+
+      i.pop();
+      o << i.indent() << "}\n";
+    }
+
+    // Returns the number of fanout produced by the filter.  More fanout implies
+    // the filter distinguishes more categories of instructions.
+    unsigned usefulness() const {
+      if (fVariableInstructions.size())
+        return fFilteredInstructions.size();
+      else
+        return fFilteredInstructions.size() - 1;
+    }
+  };
+
+  friend class Filter;
+
+  // Vector of codegen instructions to choose our filter.
+  const std::vector<const CodeGenInstruction*>& fAllInstructions;
+
+  // Vector of uid's for this filter chooser to work on.
+  const std::vector<unsigned> fInstructionsToFilter;
+
+  // Vector of candidate filters.
+  std::vector<Filter> fFilters;
+
+  // Array of bit values passed down from our parent.
+  // Set to all BIT_UNFILTERED's for fRarent == NULL.
+  bitValue_t fFiltered[tBitWidth];
+
+  // Link to the FilterChooser in our parent chain.
+  FilterChooser* fParent;
+  
+  // Index of the best filter from fFilters.
+  int fBestIndex;
+
+public:
+  FilterChooser(const FilterChooser& fc) :
+    AbstractFilterChooser(),
+    fAllInstructions(fc.fAllInstructions),
+    fInstructionsToFilter(fc.fInstructionsToFilter),
+    fFilters(fc.fFilters),
+    fParent(fc.fParent),
+    fBestIndex(fc.fBestIndex)
+  {
+    memcpy(fFiltered, fc.fFiltered, sizeof(fFiltered));
+  }
+
+  FilterChooser(const std::vector<const CodeGenInstruction*>& allInstructions,
+                const std::vector<unsigned>& instructionsToFilter) :
+    fAllInstructions(allInstructions),
+    fInstructionsToFilter(instructionsToFilter),
+    fFilters(),
+    fParent(NULL),
+    fBestIndex(-1)
+  {
+    unsigned bitIndex;
+
+    for (bitIndex = 0; bitIndex < tBitWidth; bitIndex++)
+      fFiltered[bitIndex] = BIT_UNFILTERED;
+
+    doFilter();
+  }
+
+  FilterChooser(const std::vector<const CodeGenInstruction*>& allInstructions,
+                const std::vector<unsigned>& instructionsToFilter,
+                bitValue_t (&lastFiltered)[tBitWidth],
+                FilterChooser& parent) :
+    fAllInstructions(allInstructions),
+    fInstructionsToFilter(instructionsToFilter),
+    fFilters(),
+    fParent(&parent),
+    fBestIndex(-1)
+  {
+    unsigned bitIndex;
+
+    for (bitIndex = 0; bitIndex < tBitWidth; bitIndex++)
+      fFiltered[bitIndex] = lastFiltered[bitIndex];
+
+    doFilter();
+  }
+
+  void emitTop(std::ostream& o, Indenter& i) {
+    switch(tBitWidth) {
+    case 8:
+      o << i.indent() << "typedef uint8_t field_t;\n";
+      break;
+    case 16:
+      o << i.indent() << "typedef uint16_t field_t;\n";
+      break;
+    case 32:
+      o << i.indent() << "typedef uint32_t field_t;\n";
+      break;
+    case 64:
+      o << i.indent() << "typedef uint64_t field_t;\n";
+      break;
+    default:
+      assert(0 && "Unexpected instruction size!");
+    }
+
+    o << '\n';
+
+    o << i.indent() << "field_t fieldFromInstruction(field_t insn, unsigned startBit, unsigned numBits)\n";
+
+    o << i.indent() << "{\n";
+    i.push();
+    {
+      o << i.indent() << "assert(startBit + numBits <= " << tBitWidth << " && \"Instruction field out of bounds!\");\n";
+      o << '\n';
+      o << i.indent() << "field_t fieldMask;\n";
+      o << '\n';
+      o << i.indent() << "if (numBits == " << tBitWidth << ")\n";
+
+      i.push();
+      {
+        o << i.indent() << "fieldMask = (field_t)-1;\n";
+      }
+      i.pop();
+
+      o << i.indent() << "else\n";
+
+      i.push();
+      {
+        o << i.indent() << "fieldMask = ((1 << numBits) - 1) << startBit;\n";
+      }
+      i.pop();
+
+      o << '\n';
+      o << i.indent() << "return (insn & fieldMask) >> numBits;\n";
+    }
+    i.pop();
+    o << i.indent() << "}\n";
+
+    o << '\n';
+
+    o << i.indent() << "uint16_t decodeInstruction(field_t insn) {\n";
+
+    i.push();
+    {
+      // Emits code to decode the instructions.
+      emit(o, i);
+
+      o << '\n';
+      o << i.indent() << "return 0;\n";
+    }
+    i.pop();
+
+    o << i.indent() << "}" << std::endl;
+  }
+
+protected:
+  // Populates the insn given the uid.
+  void insnWithID(insn_t& insn, unsigned insnID) const {
+    BitsInit& bits = getBitsField(*fAllInstructions[insnID]->TheDef, "Inst");
+
+    unsigned index;
+
+    for (index = 0; index < tBitWidth; index++)
+      insn[index] = bitFromBits(bits, index);
+  }
+
+  // Returns the record name.
+  const std::string& nameWithID(unsigned insnID) const {
+    return fAllInstructions[insnID]->TheDef->getName();
+  }
+
+  // Populates the field of the insn given the start position and the number of
+  // consecutive bits to scan for.
+  //
+  // Returns false if and on the first uninitialized bit value encountered.
+  // Returns true, otherwise.
+  const bool fieldFromInsn(uint64_t& field, insn_t& insn, unsigned startBit,
+                           unsigned numBits) const {
+    unsigned bitIndex;
+
+    field = 0;
+
+    for (bitIndex = 0; bitIndex < numBits; bitIndex++) {
+      if (insn[startBit + bitIndex] == BIT_UNSET)
+        return false;
+
+      if (insn[startBit + bitIndex] == BIT_TRUE)
+        field = field | (1 << bitIndex);
+    }
+
+    return true;
+  }
+
+  void dumpFilterArray(std::ostream& o, bitValue_t (&filter)[tBitWidth]) {
+    unsigned bitIndex;
+
+    for (bitIndex = tBitWidth; bitIndex > 0; bitIndex--) {
+      switch (filter[bitIndex - 1]) {
+      case BIT_UNFILTERED:
+        o << ".";
+        break;
+      case BIT_UNSET:
+        o << "_";
+        break;
+      case BIT_TRUE:
+        o << "1";
+        break;
+      case BIT_FALSE:
+        o << "0";
+        break;
+      }
+    }
+  }
+
+  void dumpStack(std::ostream& o, const char* prefix) {
+    FilterChooser* current = this;
+
+    while (current) {
+      o << prefix;
+
+      dumpFilterArray(o, current->fFiltered);
+
+      o << std::endl;
+
+      current = current->fParent;
+    }
+  }
+
+  Filter& bestFilter() {
+    assert(fBestIndex != -1 && "fBestIndex not set");
+    return fFilters[fBestIndex];
+  }
+
+  // States of our finite state machines.
+  typedef enum {
+    ATTR_NONE,
+    ATTR_FILTERED,
+    ATTR_ALL_SET,
+    ATTR_ALL_UNSET,
+    ATTR_MIXED
+  } bitAttr_t;
+
+  bool filterProcessor(bool allowMixed = true) {
+    fFilters.clear();
+    unsigned numInstructions = fInstructionsToFilter.size();
+
+    assert(numInstructions && "Filter created with no instructions");
+
+    // No further filtering is necessary.
+    if (numInstructions == 1)
+      return true;
+
+    unsigned bitIndex, insnIndex;
+
+    // We maintain tBitWidth copies of the bitAttrs automaton.
+    // The automaton consumes the corresponding bit from each
+    // instruction.
+    //
+    //   Input symbols: 0, 1, and _ (unset).
+    //   States:        NONE, FILTERED, ALL_SET, ALL_UNSET, and MIXED.
+    //   Initial state: NONE.
+    //
+    // (NONE) ------- [01] -> (ALL_SET)
+    // (NONE) ------- _ ----> (ALL_UNSET)
+    // (ALL_SET) ---- [01] -> (ALL_SET)
+    // (ALL_SET) ---- _ ----> (MIXED)
+    // (ALL_UNSET) -- [01] -> (MIXED)
+    // (ALL_UNSET) -- _ ----> (ALL_UNSET)
+    // (MIXED) ------ . ----> (MIXED)
+    // (FILTERED)---- . ----> (FILTERED)
+
+    bitAttr_t bitAttrs[tBitWidth];
+
+    // FILTERED bit positions provide no entropy and are not worthy of pursuing.
+    // Filter::recurse() set either BIT_TRUE or BIT_FALSE for each position.
+    for (bitIndex = 0; bitIndex < tBitWidth; ++bitIndex)
+      if (fFiltered[bitIndex] == BIT_TRUE || fFiltered[bitIndex] == BIT_FALSE)
+        bitAttrs[bitIndex] = ATTR_FILTERED;
+      else
+        bitAttrs[bitIndex] = ATTR_NONE;
+
+    for (insnIndex = 0; insnIndex < numInstructions; ++insnIndex) {
+      insn_t insn;
+
+      insnWithID(insn, fInstructionsToFilter[insnIndex]);
+
+      for (bitIndex = 0; bitIndex < tBitWidth; ++bitIndex) {
+        switch (bitAttrs[bitIndex]) {
+        case ATTR_NONE:
+          if (insn[bitIndex] == BIT_UNSET)
+            bitAttrs[bitIndex] = ATTR_ALL_UNSET;
+          else
+            bitAttrs[bitIndex] = ATTR_ALL_SET;
+          break;
+        case ATTR_ALL_SET:
+          if (insn[bitIndex] == BIT_UNSET)
+            bitAttrs[bitIndex] = ATTR_MIXED;
+          break;
+        case ATTR_ALL_UNSET:
+          if (insn[bitIndex] != BIT_UNSET)
+            bitAttrs[bitIndex] = ATTR_MIXED;
+          break;
+        case ATTR_MIXED:
+        case ATTR_FILTERED:
+          break;
+        }
+      }
+    }
+
+    // The regionAttr automaton consumes the bitAttrs automatons' state,
+    // lowest-to-highest.
+    //
+    //   Input symbols: F(iltered), (all_)S(et), (all_)U(nset), M(ixed)
+    //   States:        NONE, ALL_SET, MIXED
+    //   Initial state: NONE
+    //
+    // (NONE) ----- F --> (NONE)
+    // (NONE) ----- S --> (ALL_SET)     ; and set region start
+    // (NONE) ----- U --> (NONE)
+    // (NONE) ----- M --> (MIXED)       ; and set region start
+    // (ALL_SET) -- F --> (NONE)        ; and report an ALL_SET region
+    // (ALL_SET) -- S --> (ALL_SET)
+    // (ALL_SET) -- U --> (NONE)        ; and report an ALL_SET region
+    // (ALL_SET) -- M --> (MIXED)       ; and report an ALL_SET region
+    // (MIXED) ---- F --> (NONE)        ; and report a MIXED region
+    // (MIXED) ---- S --> (ALL_SET)     ; and report a MIXED region
+    // (MIXED) ---- U --> (NONE)        ; and report a MIXED region
+    // (MIXED) ---- M --> (MIXED)
+
+    bitAttr_t regionAttr = ATTR_NONE;
+
+    unsigned startBit = 0;
+
+    for (bitIndex = 0; bitIndex < tBitWidth; bitIndex++) {
+      bitAttr_t bitAttr = bitAttrs[bitIndex];
+
+      assert(bitAttr != ATTR_NONE && "Bit without attributes");
+
+#define SET_START                                                              \
+      startBit = bitIndex;
+
+#define REPORT_REGION                                                          \
+      if (regionAttr == ATTR_MIXED && allowMixed)                              \
+        fFilters.push_back(Filter(*this, startBit, bitIndex - startBit, true));\
+      else if (regionAttr == ATTR_ALL_SET && !allowMixed)                      \
+        fFilters.push_back(Filter(*this, startBit, bitIndex - startBit, false));
+
+      switch (regionAttr) {
+      case ATTR_NONE:
+        switch (bitAttr) {
+        case ATTR_FILTERED:
+          break;
+        case ATTR_ALL_SET:
+          SET_START
+          regionAttr = ATTR_ALL_SET;
+          break;
+        case ATTR_ALL_UNSET:
+          break;
+        case ATTR_MIXED:
+          SET_START
+          regionAttr = ATTR_MIXED;
+          break;
+        default:
+          assert(0 && "Unexpected bitAttr!");
+        }
+        break;
+      case ATTR_ALL_SET:
+        switch (bitAttr) {
+        case ATTR_FILTERED:
+          REPORT_REGION
+          regionAttr = ATTR_NONE;
+          break;
+        case ATTR_ALL_SET:
+          break;
+        case ATTR_ALL_UNSET:
+          REPORT_REGION
+          regionAttr = ATTR_NONE;
+          break;
+        case ATTR_MIXED:
+          REPORT_REGION
+          SET_START
+          regionAttr = ATTR_MIXED;
+          break;
+        default:
+          assert(0 && "Unexpected bitAttr!");
+        }
+        break;
+      case ATTR_MIXED:
+        switch (bitAttr) {
+        case ATTR_FILTERED:
+          REPORT_REGION
+          SET_START
+          regionAttr = ATTR_NONE;
+          break;
+        case ATTR_ALL_SET:
+          REPORT_REGION
+          SET_START
+          regionAttr = ATTR_ALL_SET;
+          break;
+        case ATTR_ALL_UNSET:
+          REPORT_REGION
+          regionAttr = ATTR_NONE;
+          break;
+        case ATTR_MIXED:
+          break;
+        default:
+          assert(0 && "Unexpected bitAttr!");
+        }
+        break;
+      case ATTR_ALL_UNSET:
+        assert(0 && "regionAttr state machine has no ATTR_UNSET state");
+      case ATTR_FILTERED:
+        assert(0 && "regionAttr state machine has no ATTR_FILTERED state");
+      }
+    }
+
+    // At the end, if we're still in ALL_SET or MIXED states, report a region
+
+    switch (regionAttr) {
+    case ATTR_NONE:
+      break;
+    case ATTR_FILTERED:
+      break;
+    case ATTR_ALL_SET:
+      REPORT_REGION
+      break;
+    case ATTR_ALL_UNSET:
+      break;
+    case ATTR_MIXED:
+      REPORT_REGION
+      break;
+    }
+
+#undef SET_START
+#undef REPORT_REGION
+
+    bool allAreUseless = true;
+    fBestIndex = 0;
+    unsigned bestUsefulness = 0;
+    unsigned filterIndex;
+    unsigned numFilters = fFilters.size();
+
+    for (filterIndex = 0; filterIndex < numFilters; ++filterIndex) {
+      unsigned usefulness = fFilters[filterIndex].usefulness();
+
+      if (usefulness)
+        allAreUseless = false;
+
+      if (usefulness > bestUsefulness) {
+        fBestIndex = filterIndex;
+        bestUsefulness = usefulness;
+      }
+    }
+
+    if (!allAreUseless) {
+      bestFilter().recurse();
+    }
+
+    return !allAreUseless;
+  } // end of filterProcessor(bool)
+
+  // Decides on the best configuration of filter(s) to use in order to decode
+  // the instructions.  A conflict of instructions may occur, in which case we
+  // dump the conflict set to the standard error.
+  void doFilter() {
+    unsigned numInstructions = fInstructionsToFilter.size();
+    assert(numInstructions && "FilterChooser created with no instructions");
+
+    if (filterProcessor(false))
+      return;
+
+    if (filterProcessor(true))
+      return;
+
+    // If we come to here, the instruction decoding has failed.
+    // Print out the instructions in the conflict set...
+
+    fBestIndex = -1;
+
+    std::cerr << "Conflict:" << std::endl;
+
+    unsigned insnIndex;
+
+    dumpStack(std::cerr, "                    ");
+
+    for (insnIndex = 0; insnIndex < numInstructions; insnIndex++) {
+      const std::string& name = nameWithID(fInstructionsToFilter[insnIndex]);
+
+      std::cerr << "    " << std::setw(15) << std::left << name << " ";
+      dumpBits(std::cerr,
+               getBitsField(*fAllInstructions[
+                              fInstructionsToFilter[insnIndex]]->TheDef,
+                            "Inst"));
+      std::cerr << std::endl;
+    }
+  }
+
+  // Emits code to decode our share of instructions.  Returns true if the
+  // emitted code causes a return, which occurs if we known how to decode
+  // the instruction at this level or the instruction is not decodeable.
+  bool emit(std::ostream& o, Indenter& i) {
+    if (fInstructionsToFilter.size() == 1) {
+      // There is only one instruction in the set, which is great!
+      // Lets return the decoded instruction.
+      o << i.indent() << "return " << fInstructionsToFilter[0] << "; // "
+        << nameWithID(fInstructionsToFilter[0]) << '\n';
+      return true;
+    } else if (fBestIndex == -1) {
+      if (fInstructionsToFilter.size() == 2) {
+        // Resolve the known conflicts sets:
+        //
+        // 1. source registers are identical => VMOVD; otherwise => VORRd
+        // 2. source registers are identical => VMOVQ; otherwise => VORRq
+        const std::string& name1 = nameWithID(fInstructionsToFilter[0]);
+        const std::string& name2 = nameWithID(fInstructionsToFilter[1]);
+        if ((name1 == "VMOVD" && name2 == "VORRd") ||
+            (name1 == "VMOVQ" && name2 == "VORRq")) {
+          // Inserting the opening curly brace for this case block.
+          i.pop();
+          o << i.indent() << "{\n";
+          i.push();
+
+          o << i.indent() <<
+            "field_t N = fieldFromInstruction(insn, 7, 1), M = fieldFromInstruction(insn, 5, 1);\n";
+          o << i.indent() <<
+            "field_t Vn = fieldFromInstruction(insn, 16, 4), Vm = fieldFromInstruction(insn, 0, 4);\n";
+          o << i.indent() << "return (N == M && Vn == Vm) ? "
+            << fInstructionsToFilter[0] << " /* " << name1 << " */ : "
+            << fInstructionsToFilter[1] << " /* " << name2 << " */ ;\n";
+
+          // Inserting the closing curly brace for this case block.
+          i.pop();
+          o << i.indent() << "}\n";
+          i.push();
+
+          return true;
+        }
+        // Otherwise, it does not belong to the known conflict sets.
+      }
+      // We don't know how to decode this instruction!  Dump the conflict set!
+      o << i.indent() << "return 0;" << " // Conflict set: ";
+      for (int i = 0, N = fInstructionsToFilter.size(); i < N; ++i) {
+        o << nameWithID(fInstructionsToFilter[i]);
+        if (i < (N - 1))
+          o << ", ";
+        else
+          o << '\n';
+      }
+      return true;
+    } else {
+      // Choose the best filter to do the decodings!
+      bestFilter().emit(o, i);
+      return false;
+    }
+  }
+};
+
+#pragma mark Backend
+
+class RISCDisassemblerEmitter::RISCDEBackend {
+public:
+  RISCDEBackend(RISCDisassemblerEmitter& frontend) :
+    fNumberedInstructions(),
+    fTopLevelInstructions(),
+    fFrontend(frontend),
+    fTarget(),
+    fFilterChooser(NULL)
+  {
+    populateInstructions();
+
+    if (fTarget.getName() == "ARM") {
+      fTargetName = TARGET_ARM;
+    } else {
+      std::cerr << "Target name " << fTarget.getName() << " not recognized" << std::endl;
+      assert(0 && "Unknown target");
+    }
+  }
+
+  ~RISCDEBackend() {
+    if (fFilterChooser) {
+      delete fFilterChooser;
+      fFilterChooser = NULL;
+    }
+  }
+
+  void getInstructionsByEnumValue(std::vector<const CodeGenInstruction*>& 
+                                  numberedInstructions) {
+    // Dig down to the proper namespace.  Code shamelessly stolen from
+    // InstrEnumEmitter.cpp
+    std::string Namespace;
+    CodeGenTarget::inst_iterator II, E;
+
+    for (II = fTarget.inst_begin(), E = fTarget.inst_end(); II != E; ++II)
+      if (II->second.Namespace != "TargetInstrInfo") {
+        Namespace = II->second.Namespace;
+        break;
+      }
+
+    assert(!Namespace.empty() && "No instructions defined.");
+
+    fTarget.getInstructionsByEnumValue(numberedInstructions);
+  }
+
+  bool populateInstruction(const CodeGenInstruction& insn) {
+    const Record& def = *insn.TheDef;
+    const std::string& name = def.getName();
+    uint8_t form = getByteField(def, "Form");
+    BitsInit& bits = getBitsField(def, "Inst");
+
+    if (fTargetName == TARGET_ARM) {
+      if (form == ARM_FORM_PSEUDO)
+        return false;
+      if (fTargetName == TARGET_ARM && name[0] == 't')
+        return false;
+      if (name.find("CMPz") != std::string::npos ||
+          name.find("CMNz") != std::string::npos)
+        return false;
+      if (name.find("BX_RET") != std::string::npos ||
+          name.find("BXr9") != std::string::npos ||
+          name.find("BLXr9") != std::string::npos)
+        return false;
+
+      //
+      // The following special cases are for conflict resolutions.
+      //
+
+      // RSCSri and RSCSrs set the 's' bit, but are not predicated.  We are
+      // better off using the generic RSCri and RSCrs instructions.
+      if (name == "RSCSri" || name == "RSCSrs") return false;
+
+      // MOVCCr, MOVCCs, MOVCCi, FCYPScc, FCYPDcc, FNEGScc, and FNEGDcc are used
+      // in the compiler to implement conditional moves.  We can ignore them in
+      // favor of their more generic versions of instructions.
+      // See also SDNode *ARMDAGToDAGISel::Select(SDValue Op).
+      if (name == "MOVCCr" || name == "MOVCCs" || name == "MOVCCi" ||
+          name == "FCPYScc" || name == "FCPYDcc" ||
+          name == "FNEGScc" || name == "FNEGDcc")
+        return false;
+
+      // Ignore the *_sfp instructions when decoding.  They are used by the
+      // compiler to implement scalar floating point operations using vector
+      // operations in order to work around some performance issues.
+      if (name.find("_sfp") != std::string::npos) return false;
+
+      // LDM_RET is a special case of LDM (Load Multiple) where the registers
+      // loaded include the PC, causing a branch to a loaded address.  Ignore
+      // the LDM_RET instruction when decoding.
+      if (name == "LDM_RET") return false;
+
+      // Bcc is in a more generic form than B.  Ignore B when decoding.
+      if (name == "B") return false;
+
+      // Ignore the non-Darwin BL instructions and the TPsoft (TLS) instruction.
+      if (name == "BL" || name == "BL_pred" || name == "TPsoft") return false;
+
+      // Ignore VDUPf[d|q] instructions known to conflict with VDUP32[d-q] for
+      // decoding.  The instruction duplicates an element from an ARM core
+      // register into every element of the destination vector.  There is no
+      // distinction between data types.
+      if (name == "VDUPfd" || name == "VDUPfq") return false;
+    }
+
+    // Dumps the instruction encoding format.
+    switch (fTargetName) {
+    case TARGET_ARM:
+      std::cerr << name << " " << stringWithARMForm((ARMForm)form);
+      break;
+    }
+
+    std::cerr << " ";
+
+    // Dumps the instruction encoding bits.
+    dumpBits(std::cerr, bits);
+
+    std::cerr << std::endl;
+
+    // Dumps the list of operand info.
+    for (unsigned i = 0, e = insn.OperandList.size(); i != e; ++i) {
+      CodeGenInstruction::OperandInfo info = insn.OperandList[i];
+      const std::string& operandName = info.Name;
+      const Record& operandDef = *info.Rec;
+
+      std::cerr << "\t" << operandName << " (" << operandDef.getName() << ") "
+                << std::endl;
+    }
+
+    return true;
+  }
+
+  void populateInstructions() {
+    getInstructionsByEnumValue(fNumberedInstructions);
+
+    uint16_t numUIDs = fNumberedInstructions.size();
+    uint16_t uid;
+
+    const char* instClass;
+
+    switch (fTargetName) {
+    case TARGET_ARM:
+      instClass = "InstARM";
+    }
+
+    for (uid = 0; uid < numUIDs; uid++) {
+      // filter out intrinsics
+      if (!fNumberedInstructions[uid]->TheDef->isSubClassOf(instClass))
+        continue;
+
+      if (populateInstruction(*fNumberedInstructions[uid]))
+        fTopLevelInstructions.push_back(uid);
+    }
+
+    switch (fTargetName) {
+    case TARGET_ARM:
+      fFilterChooser = new FilterChooser<32>(fNumberedInstructions,
+                                             fTopLevelInstructions);
+    }
+  }
+
+  // Emits disassembler code for instruction decoding.  This delegates to the
+  // FilterChooser instance to do the heavy lifting.
+  void emit(std::ostream& o) {
+    Indenter i;
+    std::string s;
+    raw_string_ostream ro(s);
+
+    switch (fTargetName) {
+    case TARGET_ARM:
+      fFrontend.EmitSourceFileHeader("ARM Disassembler", ro);
+    }
+
+    ro.flush();
+    o << s;
+
+    o << i.indent() << "#include <inttypes.h>\n";
+    o << i.indent() << "#include <assert.h>\n";
+    o << '\n';
+
+    fFilterChooser->emitTop(o, i);
+  }
+
+protected:
+  std::vector<const CodeGenInstruction*> fNumberedInstructions;
+  std::vector<unsigned> fTopLevelInstructions;
+  RISCDisassemblerEmitter& fFrontend;
+  CodeGenTarget fTarget;
+  AbstractFilterChooser* fFilterChooser;
+
+  enum {
+    TARGET_ARM = 0
+  } fTargetName;
+};
+
+#pragma mark Backend interface
+
+void RISCDisassemblerEmitter::initBackend()
+{
+    fBackend = new RISCDEBackend(*this);
+}
+
+void RISCDisassemblerEmitter::run(raw_ostream& o)
+{
+  std::ostringstream so;
+  fBackend->emit(so);
+  o << so.str();
+}
+
+void RISCDisassemblerEmitter::shutdownBackend()
+{
+  delete fBackend;
+}