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

With the help of new method readInstruction16() two bytes are read and
decodeInstruction() is called with DecoderTableMicroMips16, if this fails
four bytes are read and decodeInstruction() is called with
DecoderTableMicroMips32.

Differential Revision: http://reviews.llvm.org/D6149

llvm-svn: 222648

2 files changed, 57 insertions, 14 deletions

diff --git a/llvm/lib/Target/Mips/Disassembler/MipsDisassembler.cpp b/llvm/lib/Target/Mips/Disassembler/MipsDisassembler.cpp
index 48904ce2dee..118c3b0b293 100644
--- a/llvm/lib/Target/Mips/Disassembler/MipsDisassembler.cpp
+++ b/llvm/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,
diff --git a/llvm/lib/Target/Mips/MipsRegisterInfo.td b/llvm/lib/Target/Mips/MipsRegisterInfo.td
index 42fe76b2979..cee041fdbd4 100644
--- a/llvm/lib/Target/Mips/MipsRegisterInfo.td
+++ b/llvm/lib/Target/Mips/MipsRegisterInfo.td
@@ -289,10 +289,10 @@ def GPR32 : GPR32Class<[i32]>;
 def DSPR  : GPR32Class<[v4i8, v2i16]>;
 
 def GPRMM16 : RegisterClass<"Mips", [i32], 32, (add
-  // Return Values and Arguments
-  V0, V1, A0, A1, A2, A3,
   // Callee save
-  S0, S1)>;
+  S0, S1,
+  // Return Values and Arguments
+  V0, V1, A0, A1, A2, A3)>;
 
 def GPR64 : RegisterClass<"Mips", [i64], 64, (add
 // Reserved