Implement byte swapping instructions on MIPS32 and MIPS64.

src/mips64/disasm-mips64.cc

Index: src/mips64/disasm-mips64.cc
diff --git a/src/mips64/disasm-mips64.cc b/src/mips64/disasm-mips64.cc
index 807cc0c0685a78f34ebf934b5cfb558a5b9a9583..1917526c4220b9b7953a51a3862047eef8408e8e 100644
--- a/src/mips64/disasm-mips64.cc
+++ b/src/mips64/disasm-mips64.cc
@@ -1457,11 +1457,18 @@ void Decoder::DecodeTypeRegisterSPECIAL3(Instruction* instr) {
           Format(instr, "bitswap 'rd, 'rt");
           break;
         }
-        case SEB:
-        case SEH:
-        case WSBH:
-          UNREACHABLE();
+        case SEB: {
+          Format(instr, "seb     'rd, 'rt");
           break;
+        }
+        case SEH: {
+          Format(instr, "seh     'rd, 'rt");
+          break;
+        }
+        case WSBH: {
+          Format(instr, "wsbh    'rd, 'rt");
+          break;
+        }
         default: {
           sa >>= kBp2Bits;
           switch (sa) {
@@ -1492,10 +1499,14 @@ void Decoder::DecodeTypeRegisterSPECIAL3(Instruction* instr) {
           }
           break;
         }
-        case DSBH:
-        case DSHD:
-          UNREACHABLE();
+        case DSBH: {
+          Format(instr, "dsbh    'rd, 'rt");
+          break;
+        }
+        case DSHD: {
+          Format(instr, "dshd    'rd, 'rt");
           break;
+        }
         default: {
           sa >>= kBp3Bits;
           switch (sa) {