diff --git a/runtime/vm/compiler/assembler/assembler_ia32_test.cc b/runtime/vm/compiler/assembler/assembler_ia32_test.cc
index 715d5bb200b..3c6797b4907 100644
--- a/runtime/vm/compiler/assembler/assembler_ia32_test.cc
+++ b/runtime/vm/compiler/assembler/assembler_ia32_test.cc
@@ -4625,7 +4625,7 @@ ASSEMBLER_TEST_RUN(TestSetCC, test) {
   EXPECT_DISASSEMBLY(
       "mov eax,0xffffffff\n"
       "cmp eax,eax\n"
-      "setnz eax\n"
+      "setnz al\n"
       "ret\n");
 }
 
diff --git a/runtime/vm/compiler/assembler/assembler_x64_test.cc b/runtime/vm/compiler/assembler/assembler_x64_test.cc
index 57daebc896c..d78aa0caab6 100644
--- a/runtime/vm/compiler/assembler/assembler_x64_test.cc
+++ b/runtime/vm/compiler/assembler/assembler_x64_test.cc
@@ -675,7 +675,7 @@ ASSEMBLER_TEST_RUN(Testb3, test) {
   EXPECT_DISASSEMBLY_NOT_WINDOWS(
       "push rdi\n"
       "movl rdx,0x10\n"
-      "testb rdx,[rsp]\n"
+      "testb dl,[rsp]\n"
       "jz +13\n"
       "movl rax,1\n"
       "pop rcx\n"
@@ -5508,7 +5508,7 @@ ASSEMBLER_TEST_RUN(TestSetCC, test) {
   EXPECT_DISASSEMBLY(
       "movl rax,0xffffffff\n"
       "cmpq rax,rax\n"
-      "setnzl rax\n"
+      "setnz al\n"
       "ret\n");
 }
 
@@ -5530,7 +5530,7 @@ ASSEMBLER_TEST_RUN(TestSetCC2, test) {
       "push rbx\n"
       "movl rbx,0xffffffff\n"
       "cmpq rbx,rbx\n"
-      "setzl rdi\n"
+      "setz bh\n"
       "movq rax,rbx\n"
       "pop rbx\n"
       "ret\n");
@@ -5554,7 +5554,7 @@ ASSEMBLER_TEST_RUN(TestSetCC3, test) {
       "push r10\n"
       "movl r10,0xffffffff\n"
       "cmpq r10,r10\n"
-      "setnzl r10\n"
+      "setnz r10b\n"
       "movq rax,r10\n"
       "pop r10\n"
       "ret\n");
@@ -5578,7 +5578,7 @@ ASSEMBLER_TEST_RUN(TestSetCC4, test) {
       "push rsi\n"
       "movl rsi,0xffffffff\n"
       "cmpq rsi,rsi\n"
-      "setzl rsi\n"
+      "setz dh\n"
       "movq rax,rsi\n"
       "pop rsi\n"
       "ret\n");
diff --git a/runtime/vm/compiler/assembler/disassembler_x86.cc b/runtime/vm/compiler/assembler/disassembler_x86.cc
index fb4c917caec..d99afbf810c 100644
--- a/runtime/vm/compiler/assembler/disassembler_x86.cc
+++ b/runtime/vm/compiler/assembler/disassembler_x86.cc
@@ -314,7 +314,7 @@ class DisassemblerX64 : public ValueObject {
   }
 
   const char* NameOfByteCPURegister(int reg) const {
-    return NameOfCPURegister(reg);
+    return RegisterNames::RegisterByteName(static_cast<ByteRegister>(reg));
   }
 
   // A way to get rax or eax's name.
@@ -842,7 +842,7 @@ int DisassemblerX64::SetCC(uint8_t* data) {
   ASSERT(0x0F == *data);
   uint8_t cond = *(data + 1) & 0x0F;
   const char* mnem = conditional_code_suffix[cond];
-  Print("set%s%s ", mnem, operand_size_code());
+  Print("set%s ", mnem);
   PrintRightByteOperand(data + 2);
   return 3;  // includes 0x0F
 }
diff --git a/runtime/vm/constants.h b/runtime/vm/constants.h
index 916e23137ff..49a0889876f 100644
--- a/runtime/vm/constants.h
+++ b/runtime/vm/constants.h
@@ -60,6 +60,13 @@ class RegisterNames {
     return fpu_d_reg_names[reg];
   }
 #endif  // defined(TARGET_ARCH_ARM)
+
+#if defined(TARGET_ARCH_X64) || defined(TARGET_ARCH_IA32)
+  static const char* RegisterByteName(ByteRegister reg) {
+    ASSERT((0 <= reg) && (reg < kNumberOfByteRegisters));
+    return cpu_reg_byte_names[reg];
+  }
+#endif  // defined(TARGET_ARCH_X64) || defined(TARGET_ARCH_IA32)
 };
 
 static constexpr bool IsArgumentRegister(Register reg) {
diff --git a/runtime/vm/constants_ia32.cc b/runtime/vm/constants_ia32.cc
index 057264d9ca0..ab777c554ce 100644
--- a/runtime/vm/constants_ia32.cc
+++ b/runtime/vm/constants_ia32.cc
@@ -13,6 +13,9 @@ namespace dart {
 const char* const cpu_reg_names[kNumberOfCpuRegisters] = {
     "eax", "ecx", "edx", "ebx", "esp", "ebp", "esi", "edi"};
 
+const char* const cpu_reg_byte_names[kNumberOfCpuRegisters] = {
+    "al", "cl", "dl", "bl", "ah", "ch", "dh", "bh"};
+
 const char* const cpu_reg_abi_names[kNumberOfCpuRegisters] = {
     "eax", "ecx", "edx", "ebx", "esp", "ebp", "esi", "edi"};
 
diff --git a/runtime/vm/constants_ia32.h b/runtime/vm/constants_ia32.h
index d1412855b89..335e9b757cc 100644
--- a/runtime/vm/constants_ia32.h
+++ b/runtime/vm/constants_ia32.h
@@ -42,6 +42,7 @@ enum ByteRegister {
   CH = 5,
   DH = 6,
   BH = 7,
+  kNumberOfByteRegisters = 8,
   kNoByteRegister = -1  // Signals an illegal register.
 };
 
@@ -76,6 +77,7 @@ const FpuRegister kNoFpuRegister = kNoXmmRegister;
 
 extern const char* const cpu_reg_names[kNumberOfCpuRegisters];
 extern const char* const cpu_reg_abi_names[kNumberOfCpuRegisters];
+extern const char* const cpu_reg_byte_names[kNumberOfByteRegisters];
 extern const char* const fpu_reg_names[kNumberOfXmmRegisters];
 
 // Register aliases.
diff --git a/runtime/vm/constants_x64.cc b/runtime/vm/constants_x64.cc
index 7e03cb606a3..27c20323fde 100644
--- a/runtime/vm/constants_x64.cc
+++ b/runtime/vm/constants_x64.cc
@@ -18,6 +18,10 @@ const char* const cpu_reg_abi_names[kNumberOfCpuRegisters] = {
     "rax", "rcx", "rdx", "rbx", "rsp", "rbp", "rsi", "rdi",
     "r8",  "r9",  "r10", "r11", "r12", "r13", "r14", "r15"};
 
+const char* const cpu_reg_byte_names[kNumberOfByteRegisters] = {
+    "al",  "cl",  "dl",   "bl",   "ah",   "ch",   "dh",   "bh",
+    "r8b", "r9b", "r10b", "r11b", "r12b", "r13b", "r14b", "r15b"};
+
 const char* const fpu_reg_names[kNumberOfXmmRegisters] = {
     "xmm0", "xmm1", "xmm2",  "xmm3",  "xmm4",  "xmm5",  "xmm6",  "xmm7",
     "xmm8", "xmm9", "xmm10", "xmm11", "xmm12", "xmm13", "xmm14", "xmm15"};
diff --git a/runtime/vm/constants_x64.h b/runtime/vm/constants_x64.h
index 119f08c3c03..5128f4322e3 100644
--- a/runtime/vm/constants_x64.h
+++ b/runtime/vm/constants_x64.h
@@ -60,6 +60,7 @@ enum ByteRegister {
   R13B = 13,
   R14B = 14,
   R15B = 15,
+  kNumberOfByteRegisters = 16,
   kNoByteRegister = -1  // Signals an illegal register.
 };
 
@@ -102,6 +103,7 @@ const FpuRegister kNoFpuRegister = kNoXmmRegister;
 
 extern const char* const cpu_reg_names[kNumberOfCpuRegisters];
 extern const char* const cpu_reg_abi_names[kNumberOfCpuRegisters];
+extern const char* const cpu_reg_byte_names[kNumberOfByteRegisters];
 extern const char* const fpu_reg_names[kNumberOfXmmRegisters];
 
 enum RexBits {