X64: Do not use an AllocateWithoutSpill register if it is invalid.

src/x64/codegen-x64.cc

 // Copyright 2009 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 3066 matching lines @@
     DeferredCode* deferred = NULL;
     if (is_postfix) {
       deferred = new DeferredPostfixCountOperation(new_value.reg(),
                                                    old_value.reg(),
                                                    is_increment);
     } else {
       deferred = new DeferredPrefixCountOperation(new_value.reg(),
                                                   is_increment);
     }
 
+    // If we have a free register, combine the smi and overflow checks.
     Result tmp = allocator_->AllocateWithoutSpilling();
     ASSERT(kSmiTagMask == 1 && kSmiTag == 0);
-    __ movl(tmp.reg(), Immediate(kSmiTagMask));
-    // Smi test.
+    if (tmp.is_valid()) {
+      __ movl(tmp.reg(), Immediate(kSmiTagMask));
+    }
+
+    // Try incrementing or decrementing the smi.
     __ movq(kScratchRegister, new_value.reg());
     if (is_increment) {
       __ addl(kScratchRegister, Immediate(Smi::FromInt(1)));
     } else {
       __ subl(kScratchRegister, Immediate(Smi::FromInt(1)));
     }
-    // deferred->Branch(overflow);
-    __ cmovl(overflow, kScratchRegister, tmp.reg());
-    __ testl(kScratchRegister, tmp.reg());
-    tmp.Unuse();
-    deferred->Branch(not_zero);
+
+    // Go to the deferred case if the result overflows or is non-smi.
+    if (tmp.is_valid()){
+      __ cmovl(overflow, kScratchRegister, tmp.reg());
+      __ testl(kScratchRegister, tmp.reg());
+      tmp.Unuse();
+      deferred->Branch(not_zero);
+    } else {
+      deferred->Branch(overflow);
+      __ testl(kScratchRegister, Immediate(kSmiTagMask));
+      deferred->Branch(not_zero);
+    }
+
     __ movq(new_value.reg(), kScratchRegister);
-
     deferred->BindExit();
 
-
     // Postfix: store the old value in the allocated slot under the
     // reference.
     if (is_postfix) frame_->SetElementAt(target.size(), &old_value);
 
     frame_->Push(&new_value);
     // Non-constant: update the reference.
     if (!is_const) target.SetValue(NOT_CONST_INIT);
   }
 
   // Postfix: drop the new value and use the old.
@@ skipping 4577 matching lines @@
 int CompareStub::MinorKey() {
   // Encode the two parameters in a unique 16 bit value.
   ASSERT(static_cast<unsigned>(cc_) < (1 << 15));
   return (static_cast<unsigned>(cc_) << 1) | (strict_ ? 1 : 0);
 }
 
 
 #undef __
 
 } }  // namespace v8::internal