[Mips] Fix for decoding DINS instruction - disassembler

[spetrovic]

Summary

This patch fixes decoding of size and position for DINSM and DINSU instructions. It's different for DINS and DINSM/DINSU, I also changed test case because in this format: dinsm $4, $5, 10, 1, if position and size are 10 and 1 it's DINS, not DINSM variant. After this fix I'm able to add test case for LLVM assembler ( https://reviews.llvm.org/D30988 ).

[sdardis]

LGTM.

lib/Target/Mips/Disassembler/MipsDisassembler.cpp

 }
 
 static DecodeStatus DecodeInsSize(MCInst &Inst,
                                   unsigned Insn,
                                   uint64_t Address,
                                   const void *Decoder) {
   // First we need to grab the pos(lsb) from MCInst.
   int Pos = Inst.getOperand(2).getImm();
-  int Size = (int) Insn - Pos + 1;
+  if (Inst.getOpcode() == Mips::DINSU)
+    Pos += 32;
+  int Size;
+  if (Inst.getOpcode() == Mips::DINSM ||
+      Inst.getOpcode() == Mips::DINSU)
+    Size = (int) Insn - Pos + 33;
+  else
+    Size = (int) Insn - Pos + 1;
   Inst.addOperand(MCOperand::createImm(SignExtend32<16>(Size)));
   return MCDisassembler::Success;
 }
 
 static DecodeStatus DecodeSimm19Lsl2(MCInst &Inst, unsigned Insn,
                                      uint64_t Address, const void *Decoder) {
   Inst.addOperand(MCOperand::createImm(SignExtend32<19>(Insn) * 4));
   return MCDisassembler::Success;

test/MC/Mips/mips64extins.s

 # RUN: llvm-mc -arch=mips64el -filetype=obj -mcpu=mips64r2 -target-abi=n64 %s -o - \
 # RUN:   | llvm-objdump -disassemble - | FileCheck %s
 
         dext $2, $4, 5, 10   # CHECK: dext ${{[0-9]+}}, ${{[0-9]+}}, 5, 10
         dextu $2, $4, 34, 6  # CHECK: dextu ${{[0-9]+}}, ${{[0-9]+}}, 34, 6
         dextm $2, $4, 5, 34  # CHECK: dextm ${{[0-9]+}}, ${{[0-9]+}}, 5, 34
         dins $4, $5, 8, 10   # CHECK: dins ${{[0-9]+}}, ${{[0-9]+}}, 8, 10
-        dinsm $4, $5, 10, 1  # CHECK: dinsm ${{[0-9]+}}, ${{[0-9]+}}, 10, 1
+        dinsm $4, $5, 30, 6  # CHECK: dinsm ${{[0-9]+}}, ${{[0-9]+}}, 30, 6
         dinsu $4, $5, 40, 13 # CHECK: dinsu ${{[0-9]+}}, ${{[0-9]+}}, 40, 13