[mips][microMIPS] Implement disassembler support for 16-bit instructions

[oota-llvm.git] / lib / Target / Mips / Disassembler / MipsDisassembler.cpp

diff --git a/lib/Target/Mips/Disassembler/MipsDisassembler.cpp b/lib/Target/Mips/Disassembler/MipsDisassembler.cpp
index 48904ce2dee43c5abcfaf3dd723f747446b72d1a..118c3b0b293dacc06d5d1a6d557f24118ced617d 100644 (file)
--- a/lib/Target/Mips/Disassembler/MipsDisassembler.cpp
+++ b/lib/Target/Mips/Disassembler/MipsDisassembler.cpp
@@ -700,6 +700,26 @@ static DecodeStatus DecodeBlezGroupBranch(MCInst &MI, InsnType insn,
   return MCDisassembler::Success;
 }
 
+/// Read two bytes from the ArrayRef and return 16 bit halfword sorted
+/// according to the given endianess.
+static DecodeStatus readInstruction16(ArrayRef<uint8_t> Bytes, uint64_t Address,
+                                      uint64_t &Size, uint32_t &Insn,
+                                      bool IsBigEndian) {
+  // We want to read exactly 2 Bytes of data.
+  if (Bytes.size() < 2) {
+    Size = 0;
+    return MCDisassembler::Fail;
+  }
+
+  if (IsBigEndian) {
+    Insn = (Bytes[0] << 8) | Bytes[1];
+  } else {
+    Insn = (Bytes[1] << 8) | Bytes[0];
+  }
+
+  return MCDisassembler::Success;
+}
+
 /// Read four bytes from the ArrayRef and return 32 bit word sorted
 /// according to the given endianess
 static DecodeStatus readInstruction32(ArrayRef<uint8_t> Bytes, uint64_t Address,
@@ -711,15 +731,19 @@ static DecodeStatus readInstruction32(ArrayRef<uint8_t> Bytes, uint64_t Address,
     return MCDisassembler::Fail;
   }
 
+  // High 16 bits of a 32-bit microMIPS instruction (where the opcode is)
+  // always precede the low 16 bits in the instruction stream (that is, they
+  // are placed at lower addresses in the instruction stream).
+  //
+  // microMIPS byte ordering:
+  //   Big-endian:    0 | 1 | 2 | 3
+  //   Little-endian: 1 | 0 | 3 | 2
+
   if (IsBigEndian) {
     // Encoded as a big-endian 32-bit word in the stream.
     Insn =
         (Bytes[3] << 0) | (Bytes[2] << 8) | (Bytes[1] << 16) | (Bytes[0] << 24);
   } else {
-    // Encoded as a small-endian 32-bit word in the stream.
-    // Little-endian byte ordering:
-    //   mips32r2:   4 | 3 | 2 | 1
-    //   microMIPS:  2 | 1 | 4 | 3
     if (IsMicroMips) {
       Insn = (Bytes[2] << 0) | (Bytes[3] << 8) | (Bytes[0] << 16) |
              (Bytes[1] << 24);
@@ -738,14 +762,25 @@ DecodeStatus MipsDisassembler::getInstruction(MCInst &Instr, uint64_t &Size,
                                               raw_ostream &VStream,
                                               raw_ostream &CStream) const {
   uint32_t Insn;
-
-  DecodeStatus Result =
-      readInstruction32(Bytes, Address, Size, Insn, IsBigEndian, IsMicroMips);
-  if (Result == MCDisassembler::Fail)
-    return MCDisassembler::Fail;
+  DecodeStatus Result;
 
   if (IsMicroMips) {
-    DEBUG(dbgs() << "Trying MicroMips32 table (32-bit opcodes):\n");
+    Result = readInstruction16(Bytes, Address, Size, Insn, IsBigEndian);
+
+    DEBUG(dbgs() << "Trying MicroMips16 table (16-bit instructions):\n");
+    // Calling the auto-generated decoder function.
+    Result = decodeInstruction(DecoderTableMicroMips16, Instr, Insn, Address,
+                               this, STI);
+    if (Result != MCDisassembler::Fail) {
+      Size = 2;
+      return Result;
+    }
+
+    Result = readInstruction32(Bytes, Address, Size, Insn, IsBigEndian, true);
+    if (Result == MCDisassembler::Fail)
+      return MCDisassembler::Fail;
+
+    DEBUG(dbgs() << "Trying MicroMips32 table (32-bit instructions):\n");
     // Calling the auto-generated decoder function.
     Result = decodeInstruction(DecoderTableMicroMips32, Instr, Insn, Address,
                                this, STI);
@@ -756,6 +791,10 @@ DecodeStatus MipsDisassembler::getInstruction(MCInst &Instr, uint64_t &Size,
     return MCDisassembler::Fail;
   }
 
+  Result = readInstruction32(Bytes, Address, Size, Insn, IsBigEndian, false);
+  if (Result == MCDisassembler::Fail)
+    return MCDisassembler::Fail;
+
   if (hasCOP3()) {
     DEBUG(dbgs() << "Trying COP3_ table (32-bit opcodes):\n");
     Result =
@@ -854,7 +893,11 @@ static DecodeStatus DecodeGPRMM16RegisterClass(MCInst &Inst,
                                                unsigned RegNo,
                                                uint64_t Address,
                                                const void *Decoder) {
-  return MCDisassembler::Fail;
+  if (RegNo > 7)
+    return MCDisassembler::Fail;
+  unsigned Reg = getReg(Decoder, Mips::GPRMM16RegClassID, RegNo);
+  Inst.addOperand(MCOperand::CreateReg(Reg));
+  return MCDisassembler::Success;
 }
 
 static DecodeStatus DecodeGPR32RegisterClass(MCInst &Inst,