1 files changed, 137 insertions, 0 deletions
diff --git a/llvm/utils/TableGen/CodeBeadsGen.cpp b/llvm/utils/TableGen/CodeBeadsGen.cpp
new file mode 100644
index 000000000000..18a6d6d19eb2
--- /dev/null
+++ b/llvm/utils/TableGen/CodeBeadsGen.cpp
@@ -0,0 +1,137 @@
+//===---------- CodeBeadsGen.cpp - Code Beads Generator -------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+// CodeBeads are data fields carrying auxiliary information for instructions.
+//
+// Under the hood it's simply implemented by a `bits` field (with arbitrary
+// length) in each TG instruction description, where this TG backend will
+// generate a helper function to access it.
+//
+// This is especially useful for expressing variable length encoding
+// instructions and complex addressing modes. Since in those cases each
+// instruction is usually associated with large amount of information like
+// addressing mode details used on a specific operand. Instead of retreating to
+// ad-hoc methods to figure out these information when encoding an instruction,
+// CodeBeads provide a clean table for the instruction encoder to lookup.
+//===----------------------------------------------------------------------===//
+
+#include "CodeGenTarget.h"
+#include "llvm/ADT/StringExtras.h"
+#include "llvm/Support/Debug.h"
+#include "llvm/TableGen/Error.h"
+#include "llvm/TableGen/Record.h"
+#include "llvm/TableGen/TableGenBackend.h"
+#include <map>
+#include <string>
+#include <vector>
+using namespace llvm;
+
+namespace {
+
+class CodeBeadsGen {
+  RecordKeeper &Records;
+
+public:
+  CodeBeadsGen(RecordKeeper &R) : Records(R) {}
+  void run(raw_ostream &OS);
+};
+
+void CodeBeadsGen::run(raw_ostream &OS) {
+  CodeGenTarget Target(Records);
+  std::vector<Record *> Insts = Records.getAllDerivedDefinitions("Instruction");
+
+  // For little-endian instruction bit encodings, reverse the bit order
+  Target.reverseBitsForLittleEndianEncoding();
+
+  ArrayRef<const CodeGenInstruction *> NumberedInstructions =
+      Target.getInstructionsByEnumValue();
+
+  // Emit function declaration
+  OS << "const uint8_t *llvm::" << Target.getInstNamespace();
+  OS << "::getMCInstrBeads(unsigned Opcode) {\n";
+
+  // First, get the maximum bit length among all beads. And do some
+  // simple validation
+  unsigned MaxBitLength = 0;
+
+  for (const CodeGenInstruction *CGI : NumberedInstructions) {
+    Record *R = CGI->TheDef;
+    if (!R->getValue("Beads"))
+      continue;
+
+    BitsInit *BI = R->getValueAsBitsInit("Beads");
+    if (!BI->isComplete()) {
+      PrintFatalError(R->getLoc(), "Record `" + R->getName() +
+                                       "', bit field 'Beads' is not complete");
+    }
+
+    MaxBitLength = std::max(MaxBitLength, BI->getNumBits());
+  }
+
+  // Number of bytes
+  unsigned Parts = MaxBitLength / 8;
+
+  // Emit instruction base values
+  OS << "  static const uint8_t InstBits[][" << Parts << "] = {\n";
+  for (const CodeGenInstruction *CGI : NumberedInstructions) {
+    Record *R = CGI->TheDef;
+
+    if (R->getValueAsString("Namespace") == "TargetOpcode" ||
+        !R->getValue("Beads")) {
+      OS << "\t{ 0x0 },\t// ";
+      if (R->getValueAsBit("isPseudo"))
+        OS << "(Pseudo) ";
+      OS << R->getName() << "\n";
+      continue;
+    }
+
+    BitsInit *BI = R->getValueAsBitsInit("Beads");
+
+    // Convert to byte array:
+    // [dcba] -> [a][b][c][d]
+    OS << "\t{";
+    for (unsigned p = 0; p < Parts; ++p) {
+      unsigned Right = 8 * p;
+      unsigned Left = Right + 8;
+
+      uint8_t Value = 0;
+      for (unsigned i = Right; i != Left; ++i) {
+        unsigned Shift = i % 8;
+        if (auto *B = dyn_cast<BitInit>(BI->getBit(i))) {
+          Value |= (static_cast<uint8_t>(B->getValue()) << Shift);
+        } else {
+          PrintFatalError(R->getLoc(), "Record `" + R->getName() +
+                                           "', bit 'Beads[" + Twine(i) +
+                                           "]' is not defined");
+        }
+      }
+
+      if (p)
+        OS << ',';
+      OS << " 0x";
+      OS.write_hex(Value);
+      OS << "";
+    }
+    OS << " }," << '\t' << "// " << R->getName() << "\n";
+  }
+  OS << "\t{ 0x0 }\n  };\n";
+
+  // Emit initial function code
+  OS << "  return InstBits[Opcode];\n"
+     << "}\n\n";
+}
+
+} // End anonymous namespace
+
+namespace llvm {
+
+void EmitCodeBeads(RecordKeeper &RK, raw_ostream &OS) {
+  emitSourceFileHeader("Machine Code Beads", OS);
+  CodeBeadsGen(RK).run(OS);
+}
+
+} // namespace llvm