diff --git a/compiler/utils/x86/assembler_x86.cc b/compiler/utils/x86/assembler_x86.cc
index f2ef41f..cd30872 100644
--- a/compiler/utils/x86/assembler_x86.cc
+++ b/compiler/utils/x86/assembler_x86.cc
@@ -1708,6 +1708,13 @@
 }
 
 
+void X86Assembler::repne_scasb() {
+  AssemblerBuffer::EnsureCapacity ensured(&buffer_);
+  EmitUint8(0xF2);
+  EmitUint8(0xAE);
+}
+
+
 void X86Assembler::repne_scasw() {
   AssemblerBuffer::EnsureCapacity ensured(&buffer_);
   EmitUint8(0x66);
@@ -1716,6 +1723,13 @@
 }
 
 
+void X86Assembler::repe_cmpsb() {
+  AssemblerBuffer::EnsureCapacity ensured(&buffer_);
+  EmitUint8(0xF2);
+  EmitUint8(0xA6);
+}
+
+
 void X86Assembler::repe_cmpsw() {
   AssemblerBuffer::EnsureCapacity ensured(&buffer_);
   EmitUint8(0x66);
@@ -1731,6 +1745,13 @@
 }
 
 
+void X86Assembler::rep_movsb() {
+  AssemblerBuffer::EnsureCapacity ensured(&buffer_);
+  EmitUint8(0xF3);
+  EmitUint8(0xA4);
+}
+
+
 void X86Assembler::rep_movsw() {
   AssemblerBuffer::EnsureCapacity ensured(&buffer_);
   EmitUint8(0x66);
diff --git a/compiler/utils/x86/assembler_x86.h b/compiler/utils/x86/assembler_x86.h
index 2ddcd76..9738784 100644
--- a/compiler/utils/x86/assembler_x86.h
+++ b/compiler/utils/x86/assembler_x86.h
@@ -592,9 +592,12 @@
   void jmp(Label* label);
   void jmp(NearLabel* label);
 
+  void repne_scasb();
   void repne_scasw();
+  void repe_cmpsb();
   void repe_cmpsw();
   void repe_cmpsl();
+  void rep_movsb();
   void rep_movsw();
 
   X86Assembler* lock();
diff --git a/compiler/utils/x86/assembler_x86_test.cc b/compiler/utils/x86/assembler_x86_test.cc
index 61d70d7..9bae6c2 100644
--- a/compiler/utils/x86/assembler_x86_test.cc
+++ b/compiler/utils/x86/assembler_x86_test.cc
@@ -207,12 +207,24 @@
   DriverStr(expected, "FPUIntegerStore");
 }
 
+TEST_F(AssemblerX86Test, Repnescasb) {
+  GetAssembler()->repne_scasb();
+  const char* expected = "repne scasb\n";
+  DriverStr(expected, "Repnescasb");
+}
+
 TEST_F(AssemblerX86Test, Repnescasw) {
   GetAssembler()->repne_scasw();
   const char* expected = "repne scasw\n";
   DriverStr(expected, "Repnescasw");
 }
 
+TEST_F(AssemblerX86Test, Repecmpsb) {
+  GetAssembler()->repe_cmpsb();
+  const char* expected = "repe cmpsb\n";
+  DriverStr(expected, "Repecmpsb");
+}
+
 TEST_F(AssemblerX86Test, Repecmpsw) {
   GetAssembler()->repe_cmpsw();
   const char* expected = "repe cmpsw\n";
@@ -225,10 +237,10 @@
   DriverStr(expected, "Repecmpsl");
 }
 
-TEST_F(AssemblerX86Test, RepneScasw) {
-  GetAssembler()->repne_scasw();
-  const char* expected = "repne scasw\n";
-  DriverStr(expected, "repne_scasw");
+TEST_F(AssemblerX86Test, RepMovsb) {
+  GetAssembler()->rep_movsb();
+  const char* expected = "rep movsb\n";
+  DriverStr(expected, "rep_movsb");
 }
 
 TEST_F(AssemblerX86Test, RepMovsw) {
diff --git a/compiler/utils/x86_64/assembler_x86_64.cc b/compiler/utils/x86_64/assembler_x86_64.cc
index 1f73aa7..e9a0607 100644
--- a/compiler/utils/x86_64/assembler_x86_64.cc
+++ b/compiler/utils/x86_64/assembler_x86_64.cc
@@ -2325,6 +2325,12 @@
   EmitOperand(dst.LowBits(), src);
 }
 
+void X86_64Assembler::repne_scasb() {
+  AssemblerBuffer::EnsureCapacity ensured(&buffer_);
+  EmitUint8(0xF2);
+  EmitUint8(0xAE);
+}
+
 void X86_64Assembler::repne_scasw() {
   AssemblerBuffer::EnsureCapacity ensured(&buffer_);
   EmitUint8(0x66);
@@ -2332,7 +2338,6 @@
   EmitUint8(0xAF);
 }
 
-
 void X86_64Assembler::repe_cmpsw() {
   AssemblerBuffer::EnsureCapacity ensured(&buffer_);
   EmitUint8(0x66);
diff --git a/compiler/utils/x86_64/assembler_x86_64.h b/compiler/utils/x86_64/assembler_x86_64.h
index 3a4bfca..fdd3aa9 100644
--- a/compiler/utils/x86_64/assembler_x86_64.h
+++ b/compiler/utils/x86_64/assembler_x86_64.h
@@ -670,6 +670,7 @@
   void rolq(CpuRegister reg, const Immediate& imm);
   void rolq(CpuRegister operand, CpuRegister shifter);
 
+  void repne_scasb();
   void repne_scasw();
   void repe_cmpsw();
   void repe_cmpsl();
diff --git a/compiler/utils/x86_64/assembler_x86_64_test.cc b/compiler/utils/x86_64/assembler_x86_64_test.cc
index 48a1876..ff01429 100644
--- a/compiler/utils/x86_64/assembler_x86_64_test.cc
+++ b/compiler/utils/x86_64/assembler_x86_64_test.cc
@@ -956,6 +956,12 @@
   DriverStr(expected, "xorq");
 }
 
+TEST_F(AssemblerX86_64Test, RepneScasb) {
+  GetAssembler()->repne_scasb();
+  const char* expected = "repne scasb\n";
+  DriverStr(expected, "repne_scasb");
+}
+
 TEST_F(AssemblerX86_64Test, RepneScasw) {
   GetAssembler()->repne_scasw();
   const char* expected = "repne scasw\n";