Index: lib/Target/Mips/MicroMips32r6InstrFormats.td
===================================================================
--- lib/Target/Mips/MicroMips32r6InstrFormats.td
+++ lib/Target/Mips/MicroMips32r6InstrFormats.td
@@ -71,6 +71,20 @@
   let Inst{15-0}  = imm16;
 }
 
+class SIGN_EXTEND_FM_MMR6<string instr_asm, bits<10> funct>
+    : MMR6Arch<instr_asm> {
+  bits<5> rd;
+  bits<5> rt;
+
+  bits<32> Inst;
+
+  let Inst{31-26} = 0b000000;
+  let Inst{25-21} = rd;
+  let Inst{20-16} = rt;
+  let Inst{15-6}  = funct;
+  let Inst{5-0}   = 0b111100;
+}
+
 class PCREL19_FM_MMR6<bits<2> funct> : MipsR6Inst {
   bits<5> rt;
   bits<19> imm;
Index: lib/Target/Mips/MicroMips32r6InstrInfo.td
===================================================================
--- lib/Target/Mips/MicroMips32r6InstrInfo.td
+++ lib/Target/Mips/MicroMips32r6InstrInfo.td
@@ -36,6 +36,8 @@
 class PREF_MMR6_ENC : CACHE_PREF_FM_MMR6<0b011000, 0b0010>;
 class SUB_MMR6_ENC : ARITH_FM_MMR6<"sub", 0x190>;
 class SUBU_MMR6_ENC : ARITH_FM_MMR6<"subu", 0x1d0>;
+class SEB_MMR6_ENC : SIGN_EXTEND_FM_MMR6<"seb", 0b0010101100>;
+class SEH_MMR6_ENC : SIGN_EXTEND_FM_MMR6<"seh", 0b0011101100>;
 
 //===----------------------------------------------------------------------===//
 //
@@ -111,6 +113,8 @@
   list<Register> Defs = [AT];
 }
 
+class SEB_MMR6_DESC : SignExtInReg<"seb", i8, GPR32Opnd, II_SEB>;
+class SEH_MMR6_DESC : SignExtInReg<"seh", i16, GPR32Opnd, II_SEH>;
 class ALUIPC_MMR6_DESC_BASE<string instr_asm, RegisterOperand GPROpnd>
     : MMR6Arch<instr_asm> {
   dag OutOperandList = (outs GPROpnd:$rt);
@@ -163,4 +167,6 @@
 def PREF_MMR6 : R6MMR6Rel, PREF_MMR6_ENC, PREF_MMR6_DESC, ISA_MICROMIPS32R6;
 def SUB_MMR6 : StdMMR6Rel, SUB_MMR6_DESC, SUB_MMR6_ENC, ISA_MICROMIPS32R6;
 def SUBU_MMR6 : StdMMR6Rel, SUBU_MMR6_DESC, SUBU_MMR6_ENC, ISA_MICROMIPS32R6;
+def SEB_MMR6 : StdMMR6Rel, SEB_MMR6_DESC, SEB_MMR6_ENC, ISA_MICROMIPS32R6;
+def SEH_MMR6 : StdMMR6Rel, SEH_MMR6_DESC, SEH_MMR6_ENC, ISA_MICROMIPS32R6;
 }
Index: lib/Target/Mips/MipsInstrInfo.td
===================================================================
--- lib/Target/Mips/MipsInstrInfo.td
+++ lib/Target/Mips/MipsInstrInfo.td
@@ -1409,9 +1409,9 @@
 }
 
 /// Sign Ext In Register Instructions.
-def SEB : MMRel, SignExtInReg<"seb", i8, GPR32Opnd, II_SEB>,
+def SEB : MMRel, StdMMR6Rel, SignExtInReg<"seb", i8, GPR32Opnd, II_SEB>,
           SEB_FM<0x10, 0x20>, ISA_MIPS32R2;
-def SEH : MMRel, SignExtInReg<"seh", i16, GPR32Opnd, II_SEH>,
+def SEH : MMRel, StdMMR6Rel, SignExtInReg<"seh", i16, GPR32Opnd, II_SEH>,
           SEB_FM<0x18, 0x20>, ISA_MIPS32R2;
 
 /// Count Leading
Index: test/MC/Disassembler/Mips/micromips32r6.txt
===================================================================
--- test/MC/Disassembler/Mips/micromips32r6.txt
+++ test/MC/Disassembler/Mips/micromips32r6.txt
@@ -45,3 +45,7 @@
 
 0x00 0xa4 0x19 0xd0 # CHECK: subu $3, $4, $5
 
+0x00 0x64 0x2b 0x3c # CHECK: seb $3, $4
+
+0x00 0x64 0x3b 0x3c # CHECK: seh $3, $4
+
Index: test/MC/Mips/micromips32r6/valid.s
===================================================================
--- test/MC/Mips/micromips32r6/valid.s
+++ test/MC/Mips/micromips32r6/valid.s
@@ -21,4 +21,6 @@
   pref 1, 8($5)            # CHECK: pref 1, 8($5)       # encoding: [0x60,0x25,0x20,0x08]
   sub $3, $4, $5           # CHECK: sub $3, $4, $5      # encoding: [0x00,0xa4,0x19,0x90]
   subu $3, $4, $5          # CHECK: subu $3, $4, $5     # encoding: [0x00,0xa4,0x19,0xd0]
+  seb $3, $4               # CHECK: seb $3, $4          # encoding: [0x00,0x64,0x2b,0x3c]
+  seh $3, $4               # CHECK: seh $3, $4          # encoding: [0x00,0x64,0x3b,0x3c]