[mips][microMIPS] Fix an issue with disassembling lwm32 instruction

[zoran.jovanovic]

Summary

The microMIPS disassembler crashes on the following input:
0x21,0x3b,0x59,0x84,

[dsanders]

LGTM.

This is the llvm-mc-fuzzer generated test case isn't it? Could you mention that in your commit message?

lib/Target/Mips/Disassembler/MipsDisassembler.cpp

static DecodeStatus DecodeUImm5lsl2(MCInst &Inst, unsigned Insn,
   return MCDisassembler::Success;
 }
 
 static DecodeStatus DecodeRegListOperand(MCInst &Inst,
                                          unsigned Insn,
                                          uint64_t Address,
                                          const void *Decoder) {
   unsigned Regs[] = {Mips::S0, Mips::S1, Mips::S2, Mips::S3, Mips::S4, Mips::S5,
-                     Mips::S6, Mips::FP};
+                     Mips::S6, Mips::S7, Mips::FP};
   unsigned RegNum;
 
   unsigned RegLst = fieldFromInstruction(Insn, 21, 5);
   // Empty register lists are not allowed.
   if (RegLst == 0)
     return MCDisassembler::Fail;
 
   RegNum = RegLst & 0xf;

test/MC/Disassembler/Mips/micromips.txt

 0x40 0xa9 0x02 0x9a # CHECK: bnezc $9, 1332
 
 0x74 0x00 0x02 0x98 # CHECK: jals 1328
 
 0x03 0xe6 0x4f 0x3c # CHECK: jalrs $ra, $6
 
 0x20 0x44 0x50 0x08 # CHECK: lwm32 $16, $17, 8($4)
 
+0x21 0x3b 0x59 0x84 # CHECK: lwm32 $16, $17, $18, $19, $20, $21, $22, $23, $fp, -1660($27)
+
 0x20 0x44 0xd0 0x08 # CHECK: swm32 $16, $17, 8($4)
 
 0x22 0x04 0x90 0x08 # CHECK: swp $16, 8($4)
 
 0x22 0x04 0x10 0x08 # CHECK: lwp $16, 8($4)
 
 0x00 0x00 0x00 0x00 # CHECK: nop
 

test/MC/Disassembler/Mips/micromips_le.txt

 0xa9 0x40 0x9a 0x02 # CHECK: bnezc $9, 1332
 
 0x00 0x74 0x98 0x02 # CHECK: jals 1328
 
 0xe6 0x03 0x3c 0x4f # CHECK: jalrs $ra, $6
 
 0x44 0x20 0x08 0x50 # CHECK: lwm32 $16, $17, 8($4)
 
+0x3b 0x21 0x84 0x59 # CHECK: lwm32 $16, $17, $18, $19, $20, $21, $22, $23, $fp, -1660($27)
+
 0x44 0x20 0x08 0xd0 # CHECK: swm32 $16, $17, 8($4)
 
 0x04 0x22 0x08 0x90 # CHECK: swp $16, 8($4)
 
 0x04 0x22 0x08 0x10 # CHECK: lwp $16, 8($4)
 
 0x00 0x00 0x00 0x00 # CHECK: nop