diff --git a/src/ia32/builtins-ia32.cc b/src/ia32/builtins-ia32.cc
index 918f346d89..0a3e093056 100644
--- a/src/ia32/builtins-ia32.cc
+++ b/src/ia32/builtins-ia32.cc
@@ -399,7 +399,7 @@ void Builtins::Generate_JSConstructStubApi(MacroAssembler* masm) {
 static void Generate_JSEntryTrampolineHelper(MacroAssembler* masm,
                                              bool is_construct) {
   // Clear the context before we push it when entering the JS frame.
-  __ xor_(esi, Operand(esi));  // clear esi
+  __ Set(esi, Immediate(0));
 
   // Enter an internal frame.
   __ EnterInternalFrame();
@@ -421,7 +421,7 @@ static void Generate_JSEntryTrampolineHelper(MacroAssembler* masm,
 
   // Copy arguments to the stack in a loop.
   Label loop, entry;
-  __ xor_(ecx, Operand(ecx));  // clear ecx
+  __ Set(ecx, Immediate(0));
   __ jmp(&entry);
   __ bind(&loop);
   __ mov(edx, Operand(ebx, ecx, times_4, 0));  // push parameter from argv
@@ -644,7 +644,7 @@ void Builtins::Generate_FunctionCall(MacroAssembler* masm) {
   __ bind(&non_function);
   __ mov(Operand(esp, eax, times_4, 0), edi);
   // Clear edi to indicate a non-function being called.
-  __ xor_(edi, Operand(edi));
+  __ Set(edi, Immediate(0));
 
   // 4. Shift arguments and return address one slot down on the stack
   //    (overwriting the original receiver).  Adjust argument count to make
@@ -665,7 +665,7 @@ void Builtins::Generate_FunctionCall(MacroAssembler* masm) {
   { Label function;
     __ test(edi, Operand(edi));
     __ j(not_zero, &function, taken);
-    __ xor_(ebx, Operand(ebx));
+    __ Set(ebx, Immediate(0));
     __ GetBuiltinEntry(edx, Builtins::CALL_NON_FUNCTION);
     __ jmp(Handle<Code>(builtin(ArgumentsAdaptorTrampoline)),
            RelocInfo::CODE_TARGET);
diff --git a/src/ia32/code-stubs-ia32.cc b/src/ia32/code-stubs-ia32.cc
index a371c96393..bd95c8d0ba 100644
--- a/src/ia32/code-stubs-ia32.cc
+++ b/src/ia32/code-stubs-ia32.cc
@@ -104,7 +104,7 @@ void FastNewContextStub::Generate(MacroAssembler* masm) {
          Immediate(Smi::FromInt(length)));
 
   // Setup the fixed slots.
-  __ xor_(ebx, Operand(ebx));  // Set to NULL.
+  __ Set(ebx, Immediate(0));  // Set to NULL.
   __ mov(Operand(eax, Context::SlotOffset(Context::CLOSURE_INDEX)), ecx);
   __ mov(Operand(eax, Context::SlotOffset(Context::FCONTEXT_INDEX)), eax);
   __ mov(Operand(eax, Context::SlotOffset(Context::PREVIOUS_INDEX)), ebx);
@@ -4303,7 +4303,7 @@ void CompareStub::Generate(MacroAssembler* masm) {
       // that contains the exponent and high bit of the mantissa.
       STATIC_ASSERT(((kQuietNaNHighBitsMask << 1) & 0x80000000u) != 0);
       __ mov(edx, FieldOperand(edx, HeapNumber::kExponentOffset));
-      __ xor_(eax, Operand(eax));
+      __ Set(eax, Immediate(0));
       // Shift value and mask so kQuietNaNHighBitsMask applies to topmost
       // bits.
       __ add(edx, Operand(edx));
@@ -4433,7 +4433,7 @@ void CompareStub::Generate(MacroAssembler* masm) {
       __ j(below, &below_label, not_taken);
       __ j(above, &above_label, not_taken);
 
-      __ xor_(eax, Operand(eax));
+      __ Set(eax, Immediate(0));
       __ ret(0);
 
       __ bind(&below_label);
@@ -4646,7 +4646,7 @@ void CEntryStub::GenerateThrowTOS(MacroAssembler* masm) {
   // Before returning we restore the context from the frame pointer if
   // not NULL.  The frame pointer is NULL in the exception handler of
   // a JS entry frame.
-  __ xor_(esi, Operand(esi));  // Tentatively set context pointer to NULL.
+  __ Set(esi, Immediate(0));  // Tentatively set context pointer to NULL.
   NearLabel skip;
   __ cmp(ebp, 0);
   __ j(equal, &skip, not_taken);
@@ -4799,7 +4799,7 @@ void CEntryStub::GenerateThrowUncatchable(MacroAssembler* masm,
   }
 
   // Clear the context pointer.
-  __ xor_(esi, Operand(esi));
+  __ Set(esi, Immediate(0));
 
   // Restore fp from handler and discard handler state.
   STATIC_ASSERT(StackHandlerConstants::kFPOffset == 1 * kPointerSize);
diff --git a/src/ia32/debug-ia32.cc b/src/ia32/debug-ia32.cc
index ee9456564c..678cc93115 100644
--- a/src/ia32/debug-ia32.cc
+++ b/src/ia32/debug-ia32.cc
@@ -125,7 +125,7 @@ static void Generate_DebugBreakCallHelper(MacroAssembler* masm,
 #ifdef DEBUG
   __ RecordComment("// Calling from debug break to runtime - come in - over");
 #endif
-  __ Set(eax, Immediate(0));  // no arguments
+  __ Set(eax, Immediate(0));  // No arguments.
   __ mov(ebx, Immediate(ExternalReference::debug_break()));
 
   CEntryStub ceb(1);
diff --git a/src/ia32/ic-ia32.cc b/src/ia32/ic-ia32.cc
index 9c9304d5a4..f46b97b47f 100644
--- a/src/ia32/ic-ia32.cc
+++ b/src/ia32/ic-ia32.cc
@@ -1199,7 +1199,7 @@ void KeyedStoreIC::GenerateExternalArray(MacroAssembler* masm,
         break;
       case kExternalShortArray:
       case kExternalUnsignedShortArray:
-        __ xor_(ecx, Operand(ecx));
+        __ Set(ecx, Immediate(0));
         __ mov_w(Operand(edi, ebx, times_2, 0), ecx);
         break;
       case kExternalIntArray:
diff --git a/src/ia32/regexp-macro-assembler-ia32.cc b/src/ia32/regexp-macro-assembler-ia32.cc
index cc2f30dc12..1213448841 100644
--- a/src/ia32/regexp-macro-assembler-ia32.cc
+++ b/src/ia32/regexp-macro-assembler-ia32.cc
@@ -652,7 +652,7 @@ bool RegExpMacroAssemblerIA32::CheckSpecialCharacterClass(uc16 type,
 
 void RegExpMacroAssemblerIA32::Fail() {
   ASSERT(FAILURE == 0);  // Return value for failure is zero.
-  __ xor_(eax, Operand(eax));  // zero eax.
+  __ Set(eax, Immediate(0));
   __ jmp(&exit_label_);
 }
 
diff --git a/src/x64/assembler-x64.cc b/src/x64/assembler-x64.cc
index 8f15f23ba7..36299677df 100644
--- a/src/x64/assembler-x64.cc
+++ b/src/x64/assembler-x64.cc
@@ -74,7 +74,7 @@ void CpuFeatures::Probe(bool portable)  {
   __ xor_(rax, rdx);  // Different if CPUID is supported.
   __ j(not_zero, &cpuid);
 
-  // CPUID not supported. Clear the supported features in edx:eax.
+  // CPUID not supported. Clear the supported features in rax.
   __ xor_(rax, rax);
   __ jmp(&done);
 
diff --git a/src/x64/builtins-x64.cc b/src/x64/builtins-x64.cc
index 456d0765b9..d738261a1b 100644
--- a/src/x64/builtins-x64.cc
+++ b/src/x64/builtins-x64.cc
@@ -422,7 +422,7 @@ static void Generate_JSEntryTrampolineHelper(MacroAssembler* masm,
   // [rsp+0x20] : argv
 
   // Clear the context before we push it when entering the JS frame.
-  __ xor_(rsi, rsi);
+  __ Set(rsi, 0);
   __ EnterInternalFrame();
 
   // Load the function context into rsi.
@@ -451,7 +451,7 @@ static void Generate_JSEntryTrampolineHelper(MacroAssembler* masm,
   // rdi : function
 
   // Clear the context before we push it when entering the JS frame.
-  __ xor_(rsi, rsi);
+  __ Set(rsi, 0);
   // Enter an internal frame.
   __ EnterInternalFrame();
 
@@ -479,7 +479,7 @@ static void Generate_JSEntryTrampolineHelper(MacroAssembler* masm,
   // Register rbx points to array of pointers to handle locations.
   // Push the values of these handles.
   Label loop, entry;
-  __ xor_(rcx, rcx);  // Set loop variable to 0.
+  __ Set(rcx, 0);  // Set loop variable to 0.
   __ jmp(&entry);
   __ bind(&loop);
   __ movq(kScratchRegister, Operand(rbx, rcx, times_pointer_size, 0));
@@ -668,7 +668,7 @@ void Builtins::Generate_FunctionCall(MacroAssembler* masm) {
   //     become the receiver.
   __ bind(&non_function);
   __ movq(Operand(rsp, rax, times_pointer_size, 0), rdi);
-  __ xor_(rdi, rdi);
+  __ Set(rdi, 0);
 
   // 4. Shift arguments and return address one slot down on the stack
   //    (overwriting the original receiver).  Adjust argument count to make
@@ -689,7 +689,7 @@ void Builtins::Generate_FunctionCall(MacroAssembler* masm) {
   { Label function;
     __ testq(rdi, rdi);
     __ j(not_zero, &function);
-    __ xor_(rbx, rbx);
+    __ Set(rbx, 0);
     __ GetBuiltinEntry(rdx, Builtins::CALL_NON_FUNCTION);
     __ Jump(Handle<Code>(builtin(ArgumentsAdaptorTrampoline)),
             RelocInfo::CODE_TARGET);
diff --git a/src/x64/code-stubs-x64.cc b/src/x64/code-stubs-x64.cc
index c3eb5bf440..60ec35d06e 100644
--- a/src/x64/code-stubs-x64.cc
+++ b/src/x64/code-stubs-x64.cc
@@ -104,7 +104,7 @@ void FastNewContextStub::Generate(MacroAssembler* masm) {
   __ Move(FieldOperand(rax, FixedArray::kLengthOffset), Smi::FromInt(length));
 
   // Setup the fixed slots.
-  __ xor_(rbx, rbx);  // Set to NULL.
+  __ Set(rbx, 0);  // Set to NULL.
   __ movq(Operand(rax, Context::SlotOffset(Context::CLOSURE_INDEX)), rcx);
   __ movq(Operand(rax, Context::SlotOffset(Context::FCONTEXT_INDEX)), rax);
   __ movq(Operand(rax, Context::SlotOffset(Context::PREVIOUS_INDEX)), rbx);
@@ -250,7 +250,7 @@ void ToBooleanStub::Generate(MacroAssembler* masm) {
   __ movq(rax, Immediate(1));
   __ ret(1 * kPointerSize);
   __ bind(&false_result);
-  __ xor_(rax, rax);
+  __ Set(rax, 0);
   __ ret(1 * kPointerSize);
 }
 
@@ -2572,7 +2572,7 @@ void CEntryStub::GenerateThrowTOS(MacroAssembler* masm) {
 
   // Before returning we restore the context from the frame pointer if not NULL.
   // The frame pointer is NULL in the exception handler of a JS entry frame.
-  __ xor_(rsi, rsi);  // tentatively set context pointer to NULL
+  __ Set(rsi, 0);  // Tentatively set context pointer to NULL
   NearLabel skip;
   __ cmpq(rbp, Immediate(0));
   __ j(equal, &skip);
@@ -2756,7 +2756,7 @@ void CEntryStub::GenerateThrowUncatchable(MacroAssembler* masm,
   }
 
   // Clear the context pointer.
-  __ xor_(rsi, rsi);
+  __ Set(rsi, 0);
 
   // Restore registers from handler.
   STATIC_ASSERT(StackHandlerConstants::kNextOffset + kPointerSize ==
diff --git a/src/x64/debug-x64.cc b/src/x64/debug-x64.cc
index 2c1056f579..94a29f2249 100644
--- a/src/x64/debug-x64.cc
+++ b/src/x64/debug-x64.cc
@@ -80,7 +80,7 @@ static void Generate_DebugBreakCallHelper(MacroAssembler* masm,
 #ifdef DEBUG
   __ RecordComment("// Calling from debug break to runtime - come in - over");
 #endif
-  __ xor_(rax, rax);  // No arguments (argc == 0).
+  __ Set(rax, 0);  // No arguments (argc == 0).
   __ movq(rbx, ExternalReference::debug_break());
 
   CEntryStub ceb(1);
diff --git a/src/x64/full-codegen-x64.cc b/src/x64/full-codegen-x64.cc
index dd28d4d8c1..66bc4ede96 100644
--- a/src/x64/full-codegen-x64.cc
+++ b/src/x64/full-codegen-x64.cc
@@ -199,7 +199,7 @@ void FullCodeGenerator::Generate(CompilationInfo* info) {
 
 
 void FullCodeGenerator::ClearAccumulator() {
-  __ xor_(rax, rax);
+  __ Set(rax, 0);
 }
 
 
diff --git a/src/x64/macro-assembler-x64.cc b/src/x64/macro-assembler-x64.cc
index 1df9b4750c..70a3dab6d2 100644
--- a/src/x64/macro-assembler-x64.cc
+++ b/src/x64/macro-assembler-x64.cc
@@ -1110,7 +1110,7 @@ void MacroAssembler::SmiAnd(Register dst, Register src1, Register src2) {
 
 void MacroAssembler::SmiAndConstant(Register dst, Register src, Smi* constant) {
   if (constant->value() == 0) {
-    xor_(dst, dst);
+    Set(dst, 0);
   } else if (dst.is(src)) {
     ASSERT(!dst.is(kScratchRegister));
     Register constant_reg = GetSmiConstant(constant);
@@ -1605,7 +1605,7 @@ void MacroAssembler::DecrementCounter(StatsCounter* counter, int value) {
 #ifdef ENABLE_DEBUGGER_SUPPORT
 void MacroAssembler::DebugBreak() {
   ASSERT(allow_stub_calls());
-  xor_(rax, rax);  // no arguments
+  Set(rax, 0);  // No arguments.
   movq(rbx, ExternalReference(Runtime::kDebugBreak));
   CEntryStub ces(1);
   Call(ces.GetCode(), RelocInfo::DEBUG_BREAK);
diff --git a/src/x64/macro-assembler-x64.h b/src/x64/macro-assembler-x64.h
index d8f2fba42a..30b9ba5152 100644
--- a/src/x64/macro-assembler-x64.h
+++ b/src/x64/macro-assembler-x64.h
@@ -1176,7 +1176,7 @@ void MacroAssembler::SmiMul(Register dst,
     jmp(on_not_smi_result);
 
     bind(&zero_correct_result);
-    xor_(dst, dst);
+    Set(dst, 0);
 
     bind(&correct_result);
   } else {
diff --git a/src/x64/regexp-macro-assembler-x64.cc b/src/x64/regexp-macro-assembler-x64.cc
index 0838ddd461..27f3482a9a 100644
--- a/src/x64/regexp-macro-assembler-x64.cc
+++ b/src/x64/regexp-macro-assembler-x64.cc
@@ -688,7 +688,7 @@ bool RegExpMacroAssemblerX64::CheckSpecialCharacterClass(uc16 type,
 
 void RegExpMacroAssemblerX64::Fail() {
   ASSERT(FAILURE == 0);  // Return value for failure is zero.
-  __ xor_(rax, rax);  // zero rax.
+  __ Set(rax, 0);
   __ jmp(&exit_label_);
 }