llvm/utils/TableGen/CodeBeadsGen.cpp

   1 //===---------- CodeBeadsGen.cpp - Code Beads Generator -------------------===//
   2 //
   3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
   4 // See https://llvm.org/LICENSE.txt for license information.
   5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
   6 //
   7 //===----------------------------------------------------------------------===//
   8 // CodeBeads are data fields carrying auxiliary information for instructions.
   9 //
  10 // Under the hood it's simply implemented by a `bits` field (with arbitrary
  11 // length) in each TG instruction description, where this TG backend will
  12 // generate a helper function to access it.
  13 //
  14 // This is especially useful for expressing variable length encoding
  15 // instructions and complex addressing modes. Since in those cases each
  16 // instruction is usually associated with large amount of information like
  17 // addressing mode details used on a specific operand. Instead of retreating to
  18 // ad-hoc methods to figure out these information when encoding an instruction,
  19 // CodeBeads provide a clean table for the instruction encoder to lookup.
  20 //===----------------------------------------------------------------------===//
  21
  22 #include "CodeGenTarget.h"
  23 #include "llvm/ADT/StringExtras.h"
  24 #include "llvm/Support/Debug.h"
  25 #include "llvm/TableGen/Error.h"
  26 #include "llvm/TableGen/Record.h"
  27 #include "llvm/TableGen/TableGenBackend.h"
  28 #include <map>
  29 #include <string>
  30 #include <vector>
  31 using namespace llvm;
  32
  33 namespace {
  34
  35 class CodeBeadsGen {
  36   RecordKeeper &Records;
  37
  38 public:
  39   CodeBeadsGen(RecordKeeper &R) : Records(R) {}
  40   void run(raw_ostream &OS);
  41 };
  42
  43 void CodeBeadsGen::run(raw_ostream &OS) {
  44   CodeGenTarget Target(Records);
  45   std::vector<Record *> Insts = Records.getAllDerivedDefinitions("Instruction");
  46
  47   // For little-endian instruction bit encodings, reverse the bit order
  48   Target.reverseBitsForLittleEndianEncoding();
  49
  50   ArrayRef<const CodeGenInstruction *> NumberedInstructions =
  51       Target.getInstructionsByEnumValue();
  52
  53   // Emit function declaration
  54   OS << "const uint8_t *llvm::" << Target.getInstNamespace();
  55   OS << "::getMCInstrBeads(unsigned Opcode) {\n";
  56
  57   // First, get the maximum bit length among all beads. And do some
  58   // simple validation
  59   unsigned MaxBitLength = 0;
  60
  61   for (const CodeGenInstruction *CGI : NumberedInstructions) {
  62     Record *R = CGI->TheDef;
  63     if (!R->getValue("Beads"))
  64       continue;
  65
  66     BitsInit *BI = R->getValueAsBitsInit("Beads");
  67     if (!BI->isComplete()) {
  68       PrintFatalError(R->getLoc(), "Record `" + R->getName() +
  69                                        "', bit field 'Beads' is not complete");
  70     }
  71
  72     MaxBitLength = std::max(MaxBitLength, BI->getNumBits());
  73   }
  74
  75   // Number of bytes
  76   unsigned Parts = MaxBitLength / 8;
  77
  78   // Emit instruction base values
  79   OS << "  static const uint8_t InstBits[][" << Parts << "] = {\n";
  80   for (const CodeGenInstruction *CGI : NumberedInstructions) {
  81     Record *R = CGI->TheDef;
  82
  83     if (R->getValueAsString("Namespace") == "TargetOpcode" ||
  84         !R->getValue("Beads")) {
  85       OS << "\t{ 0x0 },\t// ";
  86       if (R->getValueAsBit("isPseudo"))
  87         OS << "(Pseudo) ";
  88       OS << R->getName() << "\n";
  89       continue;
  90     }
  91
  92     BitsInit *BI = R->getValueAsBitsInit("Beads");
  93
  94     // Convert to byte array:
  95     // [dcba] -> [a][b][c][d]
  96     OS << "\t{";
  97     for (unsigned p = 0; p < Parts; ++p) {
  98       unsigned Right = 8 * p;
  99       unsigned Left = Right + 8;
 100
 101       uint8_t Value = 0;
 102       for (unsigned i = Right; i != Left; ++i) {
 103         unsigned Shift = i % 8;
 104         if (auto *B = dyn_cast<BitInit>(BI->getBit(i))) {
 105           Value |= (static_cast<uint8_t>(B->getValue()) << Shift);
 106         } else {
 107           PrintFatalError(R->getLoc(), "Record `" + R->getName() +
 108                                            "', bit 'Beads[" + Twine(i) +
 109                                            "]' is not defined");
 110         }
 111       }
 112
 113       if (p)
 114         OS << ',';
 115       OS << " 0x";
 116       OS.write_hex(Value);
 117       OS << "";
 118     }
 119     OS << " }," << '\t' << "// " << R->getName() << "\n";
 120   }
 121   OS << "\t{ 0x0 }\n  };\n";
 122
 123   // Emit initial function code
 124   OS << "  return InstBits[Opcode];\n"
 125      << "}\n\n";
 126 }
 127
 128 } // End anonymous namespace
 129
 130 namespace llvm {
 131
 132 void EmitCodeBeads(RecordKeeper &RK, raw_ostream &OS) {
 133   emitSourceFileHeader("Machine Code Beads", OS);
 134   CodeBeadsGen(RK).run(OS);
 135 }
 136
 137 } // namespace llvm