RISC-V: Implement common register pair framework

This commit implements common framework for aligned register pairs
(using GPRs).  This is particularly useful on following extensions:

-   'Zdinx'
-   'Zqinx' (once proposed but not ratified yet)
-   'Zpsfoperand' (a part of 'P'-extension proposal)

New operand type format is shown below:

1.  'l' (stands for "length")
2.  One of the following:
    '1' for  32-bit data (or less), (RV32: 1 register,  RV64: 1 register)
    '2' for  64-bit data            (RV32: 2 registers, RV64: 1 register)
    '4' for 128-bit data            (RV32: 4 registers, RV64: 2 registers)
3.  One of the following:
    'd' for RD
    's' for RS1
    't' for RS2
    'r' for RS3
    'u' for RS1 and RS2 (where RS1 == RS2)

gas/ChangeLog:

	* config/tc-riscv.c (riscv_ip): Add handling for "l[124][dstru]".
	(validate_riscv_insn): Likewise.

opcodes/ChangeLog:

	* riscv-dis.c (print_insn_args): Add handling for "l[124][dstru]".

gas/config/tc-riscv.c

@@ -1251,6 +1251,30 @@ validate_riscv_insn (const struct riscv_opcode *opc, int length)
 	case 'z': break; /* Zero immediate.  */
 	case '[': break; /* Unused operand.  */
 	case ']': break; /* Unused operand.  */
+	case 'l': /* Register pairs.  */
+	  switch (*++oparg)
+	    {
+	    case '1':
+	    case '2':
+	    case '4':
+	      break;
+	    default:
+	      goto unknown_validate_operand;
+	    }
+	  switch (*++oparg)
+	    {
+	    case 'd': USE_BITS (OP_MASK_RD, OP_SH_RD); break;
+	    case 's': USE_BITS (OP_MASK_RS1, OP_SH_RS1); break;
+	    case 't': USE_BITS (OP_MASK_RS2, OP_SH_RS2); break;
+	    case 'r': USE_BITS (OP_MASK_RS3, OP_SH_RS3); break;
+	    case 'u': /* RS1 == RS2.  */
+	      USE_BITS (OP_MASK_RS1, OP_SH_RS1);
+	      USE_BITS (OP_MASK_RS2, OP_SH_RS2);
+	      break;
+	    default:
+	      goto unknown_validate_operand;
+	    }
+	  break;
 	case '0': break; /* AMO displacement, must to zero.  */
 	case '1': break; /* Relaxation operand.  */
 	case 'F': /* Funct for .insn directive.  */
@@ -3021,6 +3045,54 @@ riscv_ip (char *str, struct riscv_cl_insn *ip, expressionS *imm_expr,
 		}
 	      break;
 
+	    case 'l': /* Register pairs.  */
+	      if (reg_lookup (&asarg, RCLASS_GPR, &regno))
+		{
+		  if (*asarg == ' ')
+		    ++asarg;
+
+		  unsigned dlen;
+		  switch (*++oparg)
+		    {
+		    case '1': dlen =  32; break;
+		    case '2': dlen =  64; break;
+		    case '4': dlen = 128; break;
+		    default:
+		      goto unknown_riscv_ip_operand;
+		    }
+		  char c = *++oparg;
+
+		  /* Check whether the register number is aligned properly.  */
+		  if (!(xlen >= dlen || (regno % (dlen / xlen)) == 0))
+		    break;
+
+		  /* Now the register number is valid.  Insert the number to
+		     the corresponding field(s).  */
+		  switch (c)
+		    {
+		    case 'd':
+		      INSERT_OPERAND (RD, *ip, regno);
+		      break;
+		    case 's':
+		      INSERT_OPERAND (RS1, *ip, regno);
+		      break;
+		    case 't':
+		      INSERT_OPERAND (RS2, *ip, regno);
+		      break;
+		    case 'r':
+		      INSERT_OPERAND (RS3, *ip, regno);
+		      break;
+		    case 'u':
+		      INSERT_OPERAND (RS1, *ip, regno);
+		      INSERT_OPERAND (RS2, *ip, regno);
+		      break;
+		    default:
+		      goto unknown_riscv_ip_operand;
+		    }
+		  continue;
+		}
+	      break;
+
 	    case 'D': /* Floating point RD.  */
 	    case 'S': /* Floating point RS1.  */
 	    case 'T': /* Floating point RS2.  */

opcodes/riscv-dis.c

@@ -488,6 +488,37 @@ print_insn_args (const char *oparg, insn_t l, bfd_vma pc, disassemble_info *info
 	  print (info->stream, dis_style_register, "%s", riscv_gpr_names[0]);
 	  break;
 
+	case 'l':
+	  {
+	    unsigned dlen;
+	    int regno;
+	    switch (*++oparg)
+	      {
+	      case '1': dlen =  32; break;
+	      case '2': dlen =  64; break;
+	      case '4': dlen = 128; break;
+	      default:
+		goto undefined_modifier;
+	      }
+	    switch (*++oparg)
+	      {
+	      case 'd': regno = rd; break;
+	      case 's': regno = rs1; break;
+	      case 't': regno = EXTRACT_OPERAND (RS2, l); break;
+	      case 'r': regno = EXTRACT_OPERAND (RS3, l); break;
+	      case 'u': regno = rs1; break; /* RS1 == RS2.  */
+	      default:
+		goto undefined_modifier;
+	      }
+	    /* Check whether the register number is aligned properly.  */
+	    if (xlen >= dlen || (regno % (dlen / xlen)) == 0)
+	      print (info->stream, dis_style_register, "%s",
+		     riscv_gpr_names[regno]);
+	    else
+	      print (info->stream, dis_style_text, "invalid%d", regno);
+	    break;
+	  }
+
 	case '>':
 	  print (info->stream, dis_style_immediate, "0x%x",
 		 (int)EXTRACT_OPERAND (SHAMT, l));